ANESTHETIC AGENTS

A number of diverse drugs are routinely used in the ED to induce anesthesia prior to intubation. These include thiopental, methohexital, ketamine, etomidate, and propofol. Midazolam and fentanyl may also be used; these two agents are more commonly used at low doses as conscious sedation agents (see Analgesia and Sedation). The choice of a particular anesthetic agent depends to a great extent on the experience and training of the physician and to a

TABLE 3-1 -- Rapid-Sequence Induction Protocol
1.	Preoxygenate (denitrogenize) the lungs by providing 100% oxygen by mask. If ventilatory assistance is necessary, bag gently while applying cricoid pressure.
2	Assemble required equipment: Bag-valve-mask connected to an oxygen delivery system Suction with Yankauer tip Endotracheal tube with intact cuff, stylette, syringe, tape Laryngoscope and blades, in working order Cricothyrotomy tray
3.	Check to be sure that a functioning, secure IV line is in place.
4.	Continuously monitor the cardiac rhythm and oxygen saturation.
5.	Premedicate as appropriate: Fentanyl: 2 to 3 mug/kg given at a rate of 1 to 2 mug/kg/min IV for analgesia in awake patients Atropine: 0.01 mg/kg IV push for children or adolescents (minimum dose of 0.1 mg recommended) Lidocaine: 1.5 to 2.0 mg/kg IV over 30 to 60 seconds
6.	. Induce anesthesia with one of the following agents administered intravenously: thiopental, methohexital, fentanyl, ketamine, etomidate, or propofol.
7.	Give succinylcholine 1.5 mg/kg IV push (use 2.0 mg/kg for infants and small children).
8.	Apnea, jaw relaxation, and decreased resistance to bag/mask ventilations indicate that the patient is sufficiently relaxed to proceed with intubation.
9.	Perform endotracheal intubation. If unable to intubate during the first 20-second attempt, stop and ventilate the patient with the bag-mask for 30 to 60 seconds. Follow pulse oxymetry readings as a guide.
10.	Treat bradycardia occurring during intubation with atropine 0.5 mg IV push (smaller dose for children; see item 5).
11.	Once intubation is completed, inflate the cuff and confirm endotracheal tube placement by auscultating for bilateral breath sounds and checking pulse oxymetry and capnography readings.
12.	Release cricoid pressure and secure endotracheal tube.

certain extent on institutional protocols governing use of these agents. Drugs commonly used and their doses are listed in Table 3-2 .

Barbiturates: Thiopental and Methohexital

The barbiturates, in particular thiopental, have been the traditional agents used for RSI in the operating room. These agents are used less often in the ED setting because of their

TABLE 3-2 -- Recommended Anesthetic Doses for Rapid-Sequence Induction
Drug *	Dose
Thiopental	3-5 mg/kg IV
Methohexital	1-3 mg/kg IV
Fentanyl	5-15 mug/kg IV
Ketamine	1-2 mg/kg IV
Etomidate	0.3 mg/kg IV
Propofol	2.0 mg/kg IV

reputation as cardiorespiratory depressants. Of these two agents, methohexital is used more commonly in the ED because of its extremely rapid onset and short duration of action.

Pharmacology
Following IV injection,the ultrashort-acting barbiturates bind rapidly to plasma proteins, particularly albumin. Unbound barbiturate quickly accumulates in highly vascular organs, reaching peak brain levels in as short a time as 50 seconds. The drugs then diffuse from the brain, ultimately reaching equilibrium between the intracerebral and plasma concentrations. Degradation occurs primarily in the liver, producing inactive metabolites that are excreted in the urine or gut, depending on the drug used. Single-pass hepatic clearance is substantially higher for methohexital than for thiopental, which accounts for the former drug's shorter duration of action. The period of anesthesia following a single IV dose of methohexital is 4 to 6 minutes, compared with 5 to 10 minutes for thiopental. [13] [14]

The barbiturates are central nervous system (CNS) depressants that are capable of producing mild sedation to deep coma. They do not block afferent sensory impulses to a significant extent and therefore should be used in conjunction with an analgesic agent such as fentanyl if a painful procedure is to be performed. However, it is common practice to intubate patients who have received only barbiturates. [14]

The advantages of barbiturates as adjuncts to intubation include their high potency, rapid onset, and short duration of action, traits they share with fentanyl and midazolam. The barbiturates are also known to reduce cerebral metabolism and oxygen consumption and, secondarily, cerebral blood flow and intracranial pressure (ICP). [15] [16] For this reason, thiopental is considered the agent of choice for anesthesia induction and maintenance in patients with elevated ICP. Some have stated that thiopental is the drug of choice to temporarily anesthetize the patient with a head injury before intubation. It has not been proved, however, that barbiturates exert a protective effect on the CNS when used for a short period of time during RSI. Moreover, their use in trauma patients may lead to systemic hypotension and impaired cerebral perfusion pressure that may offset the theoretic advantages of barbiturate therapy.

Dose
The recommended doseof thiopental is 3 to 5 mg/kg IV administered as a 2.5% solution over 60 seconds. Normal saline should be used as a diluent. Methohexital is given at 1 to 3 mg/kg IV over 30 to 60 seconds.

Adverse Effects
It has been stated that barbiturates are "fatally easy" to use. [14] This is an overstatement that reflects improper use of the drugs more than an inherent danger associated with their proper use. The most significant complication of barbiturate therapy is depression of the vasomotor center and myocardial contractility leading to significant hypotension. This may be particularly pronounced in the presence of hypovolemia or cardiovascular disease.

Barbiturates also depress the brainstem respiratory centers when given rapidly or in large doses. This effect may be accelerated by simultaneous treatment with opioids. Patients

with asthma or chronic bronchitis may experience bronchospasm. Laryngospasm may occur in patients who were anesthetized lightly with barbiturates during manipulation of the upper airway. Laryngospasm usually responds to positive-pressure ventilation or paralysis with succinylcholine. In addition, the high pH of the barbiturate solution can cause tissue necrosis following extravascular administration and severe pain, vessel spasm, and thrombosis following intraarterial infusion.

Etomidate
Etomidate is an ultrashort-acting nonbarbiturate hypnotic agent that has been used successfully as an anesthesia induction agent in Europe since the mid-1970s and in the United States since 1983. Only recently has it been used as an adjunct to intubation in the ED. A potentially significant benefit of etomidate in the emergency setting is its lack of cardiodepressant effects. [17] Although experience in this setting is limited, etomidate's potency, rapid onset, short duration of action, and minimal side effects suggest that it will become much more widely used.

Pharmacology
Etomidate is a carboxylated imidazole that is both water and lipid soluble. The drug rapidly accumulates in vascular organs, reaching peak brain concentrations within 1 minute of IV infusion. [18] Sleep is produced within 1 arm-brain circulation time and lasts less than 10 minutes following a single bolus infusion. [19] Redistribution of the drug is quite rapid (distribution half-life, 2.6 minutes), which accounts for the short duration of action. Etomidate is rapidly hydrolyzed in the liver and plasma, forming an inactive metabolite excreted primarily in the urine. [18]

Etomidate acts on the CNS to stimulate gamma-aminobutyric acid receptors and depress the reticular activating system. After IV infusion, etomidate produces electroencephalographic changes similar to those produced by barbiturates as patients pass rapidly through light to deep levels of surgical anesthesia. Because etomidate has no analgesic activity, [18] it should be used in conjunction with an analgesic such as fentanyl when painful conditions are being treated. Etomidate decreases cerebral oxygen consumption, cerebral blood flow, and ICP but appears to have minimal effects on cerebral perfusion pressure. [20]

Dose
The recommended dose is 0.3 mg/kg IV.There is virtually no accumulation of the drug, and anesthesia may be maintained through repeated or continuous dosing. [21]

Adverse Effects
The most common side effectsof etomidate are nausea and vomiting, pain on injection, and myoclonic jerks. [22] Pain on injection occurs in up to two thirds of cases. Use of a large vein, simultaneous saline infusion, and opioid premedication are reported to reduce this side effect. [23] Myoclonic activity has been reported in about one third of cases and is believed to be caused by disinhibition of subcortical activity rather than CNS stimulation. [18]

Ketamine
Pharmacology
Unique among anesthetic agents currently in use, ketamine produces a dissociative anesthesia characterized by excellent analgesia and amnesia despite the appearance of wakefulness. As a drug that is potent and relatively safe and possesses a rapid onset and brief duration of action, ketamine fits the profile of a drug that could be used effectively to facilitate intubation. It does, however, possess a number of pharmacologic properties that limit its use to selected circumstances.

Ketamine is a water- and lipid-soluble drug with rapid penetration into the CNS. Like the barbiturates, ketamine accumulates rapidly in highly vascular organs and then undergoes redistribution. The half-life of redistribution from plasma to peripheral tissues is 7 to 11 minutes, and the half-life of elimination is 2 to 3 hours. Degradation occurs primarily in the liver. [24]

Unlike other anesthetic agents that depress the reticular activating system, ketamine acts by interrupting association pathways between the thalamocortical and limbic systems. Characteristically, the eyes remain open, and patients exhibit spontaneous, although not purposeful, movements. Increases in blood pressure, heart rate, cardiac output, and myocardial oxygen consumption are seen--effects that are most likely mediated through the CNS. In vitro studies indicate that ketamine is a myocardial depressant, but the CNS-mediated pressor effects generally mask the direct cardiac effects. [25] [26] Respirations are initially rapid and shallow after ketamine administration, but they soon return to normal.

Other features of ketamine anesthesia include increased skeletal muscle tone, preservation of laryngeal and pharyngeal reflexes, hypersalivation, and relaxation of bronchial smooth muscle. ICP is increased, most likely as a consequence of increased cerebral blood flow. [24]

Ketamine has been recommended for anesthesia induction in children because of its relative safety and infrequency of postanesthesia emergence reactions in this group. There is no evidence, however, that it offers any advantage over commonly used agents. Ketamine also has been recommended for the unstable critically ill patient, because it does not depress the cardiovascular system. This recommendation is too vague to be useful to the clinician, and it ignores the fact that ketamine is potentially harmful in patients with cardiac ischemia (because it can increase myocardial oxygen consumption) or acute intracranial pathology (because it can increase ICP). Ketamine may be useful during hemorrhagic shock because of its cardiostimulatory effect. Its administration to patients in shock has been reported to cause a fall in blood pressure only when the shock state has been prolonged. [29] [30]

The most promising use of ketamine as an intubation adjunct has been in the setting of acute bronchospastic disease. Ketamine relaxes bronchial smooth muscle either directly, through the enhancement of sympathomimetic effects, or through the inhibition of vagal effects. Ketamine also increases bronchial secretions, which may decrease the incidence of mucus plugging commonly reported in autopsies of asthmatic patients. [31] Clinical studies have demonstrated a reduction in airway resistance and an increase in pulmonary compliance that occur within minutes of ketamine administration. L'Hommedieu and Arens [8] reported

prompt improvement in respiratory acidosis in 5 asthmatics intubated with ketamine and succinylcholine.

Dose
The recommended dose of ketamine before intubation is 1 to 2 mg/kg administered IV over 1 minute. Anesthesia occurs within 1 minute of completing the infusion and lasts approximately 5 minutes. A small dose (0.5 to 1.0 mg/kg) may be given 5 minutes after the initial dose if there is a need to maintain anesthesia. The simultaneous administration of succinylcholine and midazolam is recommended to provide adequate muscle relaxation and to decrease the incidence of postanesthesia emergence reactions.

Adverse Effects
A side effect that has greatly limited the use of ketamine is its tendency to produce postanesthesia emergence reactions, a characteristic that it has in common with the structurally similar drug phencyclidine. The reactions may be marked and distressing to the patient; symptoms include floating sensations, dizziness, blurred vision, out-of-body experiences, and vivid dreams or nightmares. The reported incidence of these reactions varies from 5 to 30%. They are less common in children than in adults.

Of the drugs that have been evaluated for their ability to suppress postanesthesia emergence reactions, the benzodiazepines show the most promise. Both diazepam and lorazepam are useful, but the latter is more effective, most likely owing to its enhanced amnestic effect. Midazolam has not been evaluated as thoroughly as have the other benzodiazepines, but it has potent amnestic effects and offers the advantage of a short duration of action. White [40] reported a 55% incidence of postemergence dreaming in patients receiving ketamine and complete suppression of dreaming with the addition of midazolam. Evidence also suggests that midazolam may inhibit the cardiostimulatory effects of ketamine.

Although ketamine produces excellent analgesia and is relatively safe, its use as an agent to facilitate intubation is somewhat limited. The widely held belief that aspiration does not occur with ketamine because of preservation of pharyngeal and laryngeal reflexes is incorrect. Moreover, ketamine does not relax skeletal muscle. The production of desired intubation conditions often requires the simultaneous administration of a paralytic agent, thereby removing any upper airway reflexes.

Propofol
Emergency department experience with propofol is limited, and it is uncertain whether it will have a significant role as an adjunct to intubation in this setting.

Pharmacology
Propofol is an alkylphenol sedative-hypnotic recently introduced for induction and maintenance of general anesthesia. The drug has no analgesic activity, but it does have an amnestic effect. It produces dose-dependent depression of consciousness ranging from light sedation to coma. Propofol is a highly lipophilic, water-insoluble compound that undergoes rapid uptake by vascular tissues, including the brain, followed soon afterward by redistribution to the muscle and fat. The drug is metabolized by the liver and excreted in the urine.

Dose
Following an induction dose of 2 mg/kg IV, hypnosis occurs within 1 minute and lasts for 5 to 10 minutes. A smaller dose (1.0 to 1.5 mg/kg) is recommended in the elderly and when simultaneously administering other CNS depressants. Because propofol has a short duration of action and patients rapidly regain consciousness, repeat bolusing is not a practical way to maintain a desired level of anesthesia or sedation. A slow drip infusion of 3 to 5 mg/kg/hour titrated to effect is the preferred technique. Conscious sedation may be achieved using a drip infusion beginning at 6 mg/kg/hour and decreasing the rate as the desired level of sedation is obtained.

Adverse Effects
Side effects of propofol include direct myocardial depression causing a moderate fall in blood pressure, particularly in the elderly, in hypovolemic patients, and when administered simultaneously with opioids. Propofol reduces cerebral blood flow and may cause mild CNS excitation activity (e.g., myoclonus, tremors, hiccups) during anesthesia induction. Pain on injection occurs commonly, even when the drug is infused slowly.

CHANGING TRACHEAL TUBES

The tracheal tube with a leaking cuff is a vexing problem, especially if the original intubation was difficult. A method of replacing the tube without losing control of the tracheal lumen is preferred. This can be achieved by passing a guide down the defective tube, withdrawing the tube while leaving the guide in place, and introducing a new tube over the guide and into the trachea.
A number of different guides have been described (e.g., simple nasogastric tubes, 18 Fr Salem sump tubes , feeding tubes), but they are poor substitutes for a designated tube exchanger such as the TTX "tracheal tube exchanger" (Sheridan Catheter Corporation, Argyle, NY) or a similar commercially available device. The advantages of the designated tube exchanger are that it is stiff enough to prevent dislodgment when the endotracheal tube is introduced, it is ready to use without modification, it has a printed scale to aid in determining depth of placement, and if replacement is prolonged, the patient may be oxygenated using the exchanger and wall oxygen.

Procedure
Prior to the procedure, the patient is properly sedated or restrained. The patient is hyperventilated before placing the guide through the existing tube. The guide is lubricated and advanced into the defective tube so that it is well within the tracheal lumen (adults, 30 cm). While applying cricoid pressure (Sellick maneuver), the defective tube is withdrawn over the guide, and care is taken not to dislodge the guide when removing the tube. The replacement tube is then slid over the guide and is gently advanced into the trachea . At this juncture, it may be helpful to perform a jaw thrust or chin lift to facilitate passage through the pharynx. Resistance may be encountered at the laryngeal inlet or vocal cords; if this occurs, withdraw the tube 1 to 2 cm, rotate it 90° counterclockwise, and readvance it. With the tube clearly in the trachea, remove the guide, inflate the cuff, and ventilate the patient. After correct placement has been verified, the new tube can be secured.
Complications are related to the time required to change the tube. A successfully performed procedure can be accomplished within 30 seconds. Laryngeal injury from forcing the guide or the tube is a possibility to consider when replacing a tube

GUIDED INTUBATION TECHNIQUES

Digital Intubation

Digital intubation is a technique that uses the index and middle finger to blindly direct the endotracheal tube into the larynx. It is particularly well adapted to the out-of-hospital situation in which a trapped victim cannot be positioned for intubation. An out-of-hospital series of 66 digitally intubated patients demonstrated an 89% success rate.

Indications and Contraindications
Digital intubation is indicated in the deeply comatose patient whose larynx cannot be visualized and who has a contraindication to nasotracheal intubation. Advantages include speed and ease of placement, immunity to anatomic constraints and other difficulties visualizing the larynx, and little neck movement. Contraindications are primarily precautions to protect the operator: digital intubation should not be attempted on any patient who presents a significant risk of biting. This includes the calm and awake patient as well as the agitated patient.

Procedure
The patient's head and neck are placed in neutral position. The operator stands at the patient's right side, facing the patient. The operator's left index and middle fingers are introduced into the right angle of the patient's mouth and are slid along the surface of the tongue until the epiglottis is palpated. The tip of epiglottis is palpated at 8 to 10 cm from the corner of the mouth in the average adult. The use of a stylet in the tube is optional; the largest reported series had good success without a stylet. For the operator with short fingers or a patient with an anterior larynx, a stylet is advantageous. If a stylet is used, it is placed in the tube and bent into the form of an open "J" with the distal end terminating in a gentle hook. A lubricated tube is introduced from the patient's left between the tongue and the rescuer's 2 fingers . The tube is cradled between 2 fingers and the tip is guided beneath the epiglottis. Gentle anterior pressure directs the tube into the larynx. If the operator has sufficiently long fingers, they can be placed posterior to the arytenoids, acting as a "backstop" for the tube to both avoid esophageal passage and to assist in laryngeal placement. If a stylet has been used, it is withdrawn at this time while simultaneously advancing the tube. An alternative to using a stylet for directing the tube anteriorly is to select an endotracheal tube with a controllable tip (Endotrol, Mallinckrodt Medical Inc, St Louis).
A variation on the technique of digital intubation has been described for intubating the newborn. Only the index finger is used to guide the tube intraorally into the larynx. The end of the tube is bent and both the tube and the finger are moistened with sterile water. The index finger of the nondominant hand follows the tongue posteriorly to easily palpate the epiglottis and paired arytenoid. The thumb of the same hand may be used to apply cricoid pressure to steady the larynx. The endotracheal tube is held in the dominant hand and advanced using the nondominant index finger as a guide . The tube snugs up (encounters subtle resistance) as it enters the trachea, and palpation of the tube through the trachea provides further confirmation of correct placement. A styletted tube, shaped in the form of a J, is usually desired until familiarity with the procedure is achieved.

Complications
The risk of esophageal intubation is always present and, being a blind procedure in deeply comatose or cardiac arrested patients, the potential for esophageal misplacement is increased. If used in patients with a gag, induction of emesis with aspiration is a possibility. A high incidence of left main stem intubations was noted in a cadaveric study, but clinical confirmation is lacking. The greatest risk seems to be to the operator, whose fingers may be bitten.

Summary
While most of the recent experience with digital intubation in adults has been out of hospital, there is no reason why it should be confined to this setting. The majority of moribund emergency department patients who defy orotracheal intubation are never given a trial of digital intubation. This omission undoubtedly deprives some patients of expeditious airway management.


Lighted Stylet Intubation

This technique uses a battery-operated lighted stylet that is placed in an endotracheal tube and used to guide the tube into the trachea by transilluminating the soft tissues of the neck. First described in 1957 by MacIntosh and Richards, it was designed to aid in intubating the difficult airway. It has also been shown to be a useful means of determining the position of the tracheal tube.
In the operating room, the Tube Stat lighted stylet (Concept Corp, Clearwater, Fla) has been 99 to 100% successful. The requirement that the overhead lights be dimmed during the procedure has limited its use in most emergency settings. In a small out-of-hospital study, 88% of patients were successfully intubated by physicians using a lighted stylet. The majority of the failures occurred in the setting of bright sunlight and in patients who had vomited. A new device (Trachlight, Laerdal, Inc, Starger, Norway) with a brighter light source and adjustable length, appears to have solved this problem. In a series of 96 patients, many with a history of difficult intubation, all but 1 were successfully intubated in ambient light with this device using either the oral or nasotracheal route. Consistent with other series, the only failure was in a morbidly obese patient.

Indications and Contraindications
The patient with a difficult airway in whom direct laryngoscopy has failed is a candidate for light-guided tracheal intubation. A multiple trauma patient with airway bleeding is a prime example. The patient who has been pharmacologically paralyzed and cannot be intubated with direct laryngoscopy is another example. The lighted stylet may also be helpful in successfully completing a difficult nasotracheal intubation. One advantage of this technique over nasotracheal intubation is that it can be used in the apneic patient.
Because lighted stylet intubation is a blind approach, it should be avoided in patients with expanding neck masses and patients with airway compromise presumed due to a foreign body. Massive obesity has been shown to be the most common cause for failure with this technique because of the impossibility of transilluminating through the generous soft tissue.

Preparation
The function of the bulb of the lighted stylet should be checked before use. The patient's head should be placed in a neutral or, if cervical spine injury is not a concern, the sniffing position. The awake patient should have the oropharynx and hypopharynx sprayed with lidocaine and sedation should be administered as indicated.

Procedure
The lubricated lighted stylet is inserted into a tracheal tube (5.5 mm or larger) until the bulb lies just distal to the side port, not protruding from the end of the tube. This unit is bent in the shape of a hockey stick that approximates a 90° curve beginning just proximal to the tube cuff. The operator stands at the head of the patient. When this is not possible, the patient can be approached from the right or the left side. The tongue is grasped with gauze and pulled forward. Another means of exposing the oropharynx is to grasp the jaw between the thumb and the fingers . The light is turned on and the unit is inserted into the mouth, following the curve of the tongue into the oropharynx. A transilluminating glow indicates the location of the tube tip. Application of cricoid pressure may enhance transillumination. The overhead light should routinely be dimmed if feasible. Positioning is optimal when the glow emanates from the midline at the level of the hyoid bone. Holding the lighted stylet steady, the tube is slid off and advanced into the trachea. If the glow is located elsewhere, the unit should be withdrawn 2 cm or cocked back and repositioned as indicated by the light. If no light is seen, the tube is in the esophagus and should be pulled back, laryngeal pressure applied, and, if necessary, the head extended slightly. After passage, the tube should be checked for correct positioning and then secured.

Complications
Earlier reports noted complications resulting from an equipment failure and lost bulbs, but these problems have been corrected. No complications have been noted in the recent literature, but this may only reflect the limited use of this technique in uncontrolled settings.

Summary
Lighted stylet intubation is a safe, rapid, and highly successful method that has a definite place in the management of the difficult airway. Recent improvements in the device will increase its applicability to most settings in which emergency airway control is required.


Intubation over a Fiberoptic Bronchoscope

The use of the flexible fiberoptic bronchoscope as an aid to tracheal intubation is a recent addition in airway management in the emergency department. In this setting, success approximates 80%, with the most common cause of failure being the inability to visualize the glottis secondary to blood and secretions.
Flexible fiberoptic endoscopy is the best method for intubating the awake patient with a difficult airway. It can be accomplished using the nasal or oral route and is better tolerated than direct laryngoscopy. It also may be effective in the comatose patient when more conventional methods have failed. It provides excellent visualization of the airway and permits the evaluation of the airway prior to tube placement. The greatest obstacle to success is the inability to see through the scope secondary to blood, secretions, or fogging. The expense of the equipment, its fragility, and the time required to achieve technical proficiency are three other drawbacks.

Indications and Contraindications
Common indications for emergency fiberoptic intubation include the unstable cervical spine, expanding neck masses, upper airway infection, facial and airway burns, and anticipation of a difficult intubation due to anatomic constraints. It may also be helpful in guiding blind nasotracheal intubation that is initially unsuccessful.
Contraindications to fiberoptic nasotracheal intubation are those ascribed to nasotracheal intubation in general: severe midface trauma and coagulopathy. Although there are no clear contraindications to fiberoptic orotracheal intubation, active airway bleeding and vomiting are relative contraindications because successful fiberoptic intubation is rarely achieved in this setting. If the operator is inexperienced in fiberoptic intubation, apnea is another relative contraindication to its use.

Equipment
Fiberoptic scopes are graded according to their external diameter (in millimeters). A convenient intubating scope is 3.5 mm. Although it is physically possible to pass a 4.0 mm (0.5 mm larger) tracheal tube over the scope, the fit is quite tight. As a rule, the tracheal tube should be at least 1 mm larger than the intubating scope. The size of the working channel--the port to which suction or oxygen is applied and through which fluid or catheters may be passed--is another important dimension when evaluating fiberoptic scopes. Large working channels are desirable.

Procedure
The optimal positioning of the neck is in extension, as opposed to the cervical flexion desired when using direct laryngoscopy. Extension allows for better visualization of the
glottis by elevating the epiglottis off the posterior pharyngeal wall. This is especially pertinent in the comatose patient who lacks the muscle tone necessary to maintain an open airway. Problems with the tongue and soft tissues falling back and obscuring fiberoptic scope view are effectively managed by applying a jaw lift or pulling the tongue forward and away from the soft palate and posterior pharyngeal wall. This maneuver also moves the epiglottis away from the posterior pharyngeal wall facilitating exposure of the cords. Extending the head on the neck may accomplish the same objective.

Nasotracheal approach.
The nasal approach is preferred to the oral approach because the angle of insertion allows for easier visualization of the larynx and because patient cooperation is not as critical. Also, in the unconscious patient, the tip of the scope is less likely to impinge on the base of the tongue with a nasal approach.
The nose is prepared using a vasoconstrictor and topical anesthetic agent as described for nasotracheal intubation. Using an aerosolized anesthetic agent, it is important to obtain sufficient hypopharyngeal anesthesia to minimize gagging and laryngospasm once the procedure begins. The well-lubricated endotracheal tube may be placed in the nostril first, and the scope passed through it, or the endotracheal tube can be mounted over the scope and the scope first passed through the nostril. The advantage of the former is that it avoids the possibility of nasal secretions covering the scope and obscuring the view. The disadvantage is that nasotracheal placement may cause bleeding as well as that in some patients, the tube may not make the bend into the nasopharynx.
The most patent nostril is prepped and the endotracheal tube is advanced until it makes the bend into the nasopharynx in the manner described under nasotracheal intubation. If negotiating this bend is difficult, a well-lubricated fiberoptic scope can be placed through the tube and into the oropharynx to serve as a guide for the endotracheal tube. Once the tracheal tube is in the oropharynx, thorough oropharyngeal suctioning should be performed prior to introduction of the scope into the endotracheal tube. The fiberoptic scope is then advanced toward the larynx; the epiglottis and vocal cords are seen with little or no manipulation of the tip of the fiberoptic scope in 90% of patients. As the scope is advanced, the cords are kept in view by frequent minor adjustments of the scope tip.
In the comatose or obtunded patient, the tongue and other soft tissue may obscure the view of the larynx; this can be alleviated by having an assistant pull the tongue forward or apply a chin or jaw lift. The scope is advanced through the larynx to the level of the midtrachea and the endotracheal tube is passed over the firmly held fiberoptic scope into the trachea . It is helpful to remember that in adults the average distance from the naris to the epiglottis is 16 to 17 cm; if the scope has been advanced much beyond this distance and the glottis is still not seen, the scope is probably in the esophagus. If the scope meets resistance at about this same level and only a pink blur is visible, the scope tip is probably in a piriform sinus; transillumination of the soft tissues may be present to confirm this as well as to indicate what corrective maneuvers are necessary.
The greatest impediment to successful fiberoptic intubation is the inability to visualize the larynx because blood or secretions have covered the optical element and cannot be removed. The best time to suction is before introducing the fiberoptic scope, actively suctioning the oropharynx just prior to scope insertion. Once the scope is in place, minor secretions can be suctioned through the fiberoptic suction port. Significant blood and secretions, however, are best removed by insufflation of oxygen through the suction port and out the tip of the scope, serving simultaneously to remove blood and secretions, defog the tip, and increase the inspired O2 content. The set-up required for insufflation should be immediately available, if not already attached to the suction port prior to scope insertion. Once the scope has entered the trachea, difficulty may be encountered in advancing the endotracheal tube into the trachea. The tip of the tube most commonly catches on the right arytenoid cartilage or vocal cord; withdrawing the tube 2 cm, rotating it counterclockwise 90°, and readvancing the tube should result in successful tracheal intubation.

Orotracheal approach.
Oral fiberoptically guided intubation is indicated when contraindications to nasal intubation are present, the most common being severe midface trauma, or when the operator is more comfortable with this approach. The oral approach is more difficult than the nasal approach because the path of the scope is less defined by the surrounding soft tissue and the tip of the scope is more likely to impinge on the base of the tongue or vallecula. Attention to keeping the scope in the midline and elevating the soft tissue by pulling the tongue forward or applying the jaw lift will minimize this difficulty. Another disadvantage of the oral approach is that the oropharyngeal axis is not as well aligned with the laryngeal axis as in the nasal approach and thus requires more scope manipulation to visualize the larynx.
The drawbacks of the oral approach can be minimized by using an oral intubating airway. This adjunct resembles an oropharyngeal airway but is longer and has a cylindrical passage through which the fiberoptic scope and tracheal tube are passed. The tip of this airway lies just cephalad to the epiglottis and assures midline positioning and a predictable place from which to advance the scope.
The patient must be adequately anesthetized or obtunded to minimize the gag reflex. Topical anesthesia is achieved by spraying a 4 or 10% solution of lidocaine into the oropharynx. A degree of laryngeal and tracheal anesthesia may be achieved by a transoral spray using the laryngeal tracheal anesthetic (LTA) set. A well-lubricated fiberoptic scope, premounted with an endotracheal tube, is placed through the oral intubating airway and the trachea is fiberoptically intubated. The endotracheal tube is advanced over the scope into the trachea, frequently requiring the same counterclockwise manipulation as described with the nasal approach. After successful intubation, the intubating device can be left in place as a bite block, or it can be removed over the endotracheal tube after removal of the tube adapter. Some oral intubating airways can be removed from the mouth without disconnecting the endotracheal tube adapter.

Complications
Complications of fiberoptic orotracheal intubation include prolonged intubation attempts and vomiting and laryngospasm in the underanesthetized patient. Oxygen saturation monitoring should alert the operator to hypoxemia from prolonged intubation attempts. The majority of complications seen with fiberoptically guided nasotracheal intubation are associated with the passage of the endotracheal tube through the nasopharynx. Epistaxis is most common, followed by other nasopharyngeal injuries seen with nasotracheal intubation in general. A rare but potentially significant complication may result if on blind advancement of the fiberoptic scope through the endotracheal tube, the tip of the scope inadvertently exits out through the distal side port (Murphy's eyes) as it is being advanced through the larynx into the trachea. [74] Attempts at passing the endotracheal tube through the larynx will fail because the tube tip, now extending off the midline, will catch on the laryngeal structures. This complication is avoided if the scope is introduced prior to tracheal tube placement.

Summary
The primary advantage of fiberoptic intubation is its ability to negotiate difficult airway anatomy. It is noninvasive and well tolerated. Its major limitation in the emergency setting is lack of visibility in the presence of blood and secretions. The fiberoptic scope requires more practice than other methods of airway management; the first experience using the scope should not be in the setting of an emergency airway problem. Once familiarity and facility with the scope are acquired, fiberoptic intubation can be used early in the management of the difficult airway rather than as a last resort after repeated failed attempts using conventional techniques.

Retrograde Intubation
Retrograde orotracheal intubation is a technique of guided endotracheal intubation using a wire or catheter placed percutaneously through the cricothyroid membrane or high trachea and exiting through the mouth or nose. An endotracheal tube is then passed over this guide and advanced through the vocal cords into the trachea. Introduced by Butler and Cirillo in 1960, the technique has undergone several recent modifications that have enhanced its value as a means of establishing a definitive airway when more conventional techniques have failed.

Indications and Contraindications
Retrograde intubation is indicated when definitive airway control is required and less invasive methods have failed. Indications include trismus, ankylosis of the jaw or cervical spine, upper airway masses, unstable cervical spine injuries, and maxillofacial trauma. It can be used to convert transtracheal needle ventilation into a definitive airway. It has been described in a 1-month-old with developmental abnormalities. It is particularly helpful in the trauma patient with airway bleeding that prevents visualization of the glottis. A striking example of the efficacy of this technique is presented in an article by Barriot and Riou describing successful out-of-hospital retrograde intubation in a series of trauma patients in whom attempts at conventional intubation failed.
Contraindications to this procedure include the ability to control the airway by less invasive means. The inability to open the mouth is another contraindication. A relative contraindication is the apneic patient who cannot be effectively ventilated using the bag-valve-mask; in this setting it is advisable to first establish transtracheal needle ventilation before attempting retrograde intubation or to go directly to cricothyrotomy.

Equipment
Needed materials include the following: (1) local anesthetic and skin preparation materials, (2) 18-ga needle, (3) 60 cm epidural catheter-needle combination or 80 cm (0.88 mm diameter) spring guide wire (J-tip preferred), (4) hemostat, (5) long forceps (e.g., Magill) for grasping wire in pharynx, (6) endotracheal tube of appropriate size, (7) syringe for tube cuff, and (8) materials for securing tube. A prepackaged alternative is the Cook Retrograde Intubation Set (Cook Critical Care, Bloomington, Ind), which also contains a sheath.

Procedure
Three anatomic landmarks must be located by palpation: the hyoid bone, thyroid cartilage, and cricoid cartilage. The skin overlying the cricothyroid membrane is prepped and anesthetized. Next, the lower half of the cricothyroid membrane is punctured with a needle directed slightly cephalad. The bevel should also face cephalad. Air is aspirated to confirm needle tip position within the lumen of the larynx. An alternative entry point is the high trachea, usually through the subcricoid space, using the same steps as described for the cricothyroid membrane.
The syringe is removed and the wire is then passed through the needle and advanced until it is seen in the patient's mouth, with the help of the laryngoscope, or until it exits out the nose. If the wire is found in the hypopharynx, it is grasped with the Magill forceps and drawn out through the mouth. The needle is removed from the neck and the end of the wire is secured at the puncture site with a hemostat. The oral end of the wire is then threaded in through the endotracheal tube side port--not the end of the tube--and advanced up the tube until it can be grasped by a second hemostat. Threading the wire through the side port allows the tube tip to protrude 1 cm beyond the point at which the wire enters the larynx. The wire is then pulled taut and moved back and forth to ensure that no slack remains.
The endotracheal tube is then advanced over the wire until resistance is met. This is the most critical point in the procedure; because this is a blind technique, it may be difficult to determine whether the tube has entered the trachea or is hung up on more proximal structures. If the endotracheal tube has successfully passed through the vocal cords and it is being restricted by the guide wire as it traverses the anterior laryngeal wall, one should feel some caudally directed tension on the wire at its laryngeal insertion point. If this does not occur, the tip of the endotracheal tube may be proximal to the vocal cords, either in the vallecula, the piriform sinus, or abutting the narrow anterior aspect of the vocal cords. If in doubt, pull the tube back 2 cm, rotate it 90° counterclockwise, and readvance the tube. This will usually result in successful passage through the larynx. [73] When satisfied that the tube has entered the trachea, the tube should be stabilized and the guide wire pulled out through the mouth. The tube is then advanced further into the trachea.
The classic method of retrograde intubation, as described above, has undergone modifications that facilitate the passage of the endotracheal tube through the glottis. A significant advance has been the addition of a plastic sheath that is passed antegrade over the wire until it meets resistance at the point at which the wire penetrates the laryngeal mucosa . This sheath needs to be stiff enough to effectively guide an endotracheal tube, yet small enough to easily pass through the vocal cords without impinging on supraglottic or glottic structures. Once the sheath comes to rest against the anterior laryngeal wall, the wire is withdrawn from the mouth and the sheath is advanced. With the sheath well within the trachea, the endotracheal tube is passed over the sheath. Any resistance that may be encountered at the arytenoids or vocal cords can usually be remedied by pulling the tube back 1 to 2 cm and rotating it counterclockwise 90°. One advantage of the antegrade sheath is that it lies freely in the larynx, allowing for a more posterior passage through the widest distance between the cords. The wire, however, pulls the endotracheal tube anteriorly toward the narrow commissure of the vocal cords and is more likely to result in impingement of the tube on the cords. Also, the use of the sheath permits unrestricted advancement of the endotracheal tube, whereas a wire entering the larynx 1.0 to 1.5 cm below the vocal cords prevents the tube from advancing more than this distance prior to removal of the wire.
If no sheath is available, one should consider placing the needle inferiorly in the subcricoid space, thereby increasing the distance the endotracheal tube can be advanced before being stopped by the wire. This will decrease the likelihood of dislodging the endotracheal tube tip when the guide wire is withdrawn.
Up to this point, blind retrograde intubation has been described. A further modification of the technique allows for visualization using a fiberoptic scope. In addition to the scope, an extra long guide wire (e.g., 125 cm, 0.025 cm Teflon-coated J-wire) is also required. The procedure is the same as previously described up to the point at which the wire is withdrawn from the mouth. At that point, with a endotracheal tube mounted on a lubricated fiberoptic scope, the long guide wire is passed retrograde up through the end of the fiberoptic scope and out the suction port. The fiberoptic scope is then advanced over the guide wire and through the cords, coming to rest against the anterior laryngeal wall. The wire is withdrawn from the suction port and the scope is advanced into the trachea. The endotracheal tube is then passed over the fiberoptic scope, and visualization guarantees correct endotracheal placement. The scope is then withdrawn and the lungs are auscultated.

Complications
The complications of retrograde intubation are largely related to cricothyroid membrane puncture. Hemorrhage is minimized by taking care to puncture the cricothyroid membrane in its lower half (to avoid the cricothyroid artery). Subcutaneous emphysema may occur, but it is of no clinical significance because no air is insufflated during this technique. A small incidence of soft tissue infection is reported with translaryngeal needle procedures, but this can be minimized by ensuring that the wire is withdrawn from the mouth rather than the neck.
The final complication, the failure to achieve intubation, has been mitigated by the addition of the antegrade sheath over the wire.

Summary
Retrograde intubation is an underused technique for achieving endotracheal intubation in a patient who cannot be intubated by less aggressive means. It is more invasive than fiberoptic intubation but requires less skill. Whereas retrograde intubation usually takes several minutes to complete, [81] the patient can undergo bag-mask ventilation through much of the procedure. Recent modifications in the technique guarantee this method a prominent place in the management of the difficult airway, particularly when active bleeding compromises the airway.

NASOTRACHEAL INTUBATION

Nasotracheal intubation was first described by Magill in the 1920s and the basic technique has changed little over the years. Modifications have been described that increase the success rate and limit complications. The tube may be placed blindly or with the aid of a laryngoscope or bronchoscope. Blind nasotracheal intubation can be one of the more technically demanding airway approaches, with the outcome being heavily dependent on the skill and experience of the operator. The primary advantage of blind nasotracheal intubation is that it minimizes neck movement and does not require opening the mouth.

General Indications and Contraindications
Nasotracheal intubation is technically more difficult than oral intubation, but it has definite advantages. It is especially suitable for the patient with a short, thick neck or other anatomic characteristics that would make orotracheal intubation difficult. Patients with clenched teeth or suspected cervical spine injury can be intubated with minimal preparation. Cervical spine films, jaw spreading, or paralyzing agents as preliminaries to airway control are unnecessary.
Blind nasotracheal intubation is possible with the patient in the sitting position, a distinct advantage when intubating the patient with congestive heart failure who cannot tolerate lying flat. In fact, patients in respiratory distress are the easiest to intubate blindly because their air hunger results in increased abduction of the vocal cords, which facilitates tube entry into the trachea. The drug overdose patient with a decreased level of consciousness is a candidate for nasotracheal intubation. These patients are often intubated before gastric lavage and may be sufficiently awake to make orotracheal intubation difficult without paralyzing agents.
A nasotracheal tube has advantages that extend beyond the immediate difficulties of airway control. The patient cannot bite the tube or manipulate it with the tongue. Oral injuries may be cared for without interference by the tube. A nasotracheal tube is more easily stabilized and generally easier to care for than an orotracheal tube. It is better tolerated by the patient, permitting easier movement in bed, and produces less reflex salivation than do oral tubes.
Nasal intubation should be avoided in patients with severe nasal or midface trauma. In the presence of a basilar skull fracture, a nasotracheal tube may inadvertently enter the brain through a basilar skull fracture. [41] The technique should be avoided in patients in whom thrombolytic therapy is being considered. Nasal intubation is relatively contraindicated if the patient is taking anticoagulants or is known to have a coagulopathy.

Blind Placement
Blind nasotracheal intubation is the most common form of nasotracheal intubation in the emergency setting. Danzl and Thomas reported a success rate of 92% in a large series of emergency department patients.

Indications and Contraindications
Any patient requiring airway control who has spontaneous respirations is a candidate for blind nasotracheal intubation. Specific indications that favor this approach over others are (1) short, thick neck, (2) inability to open the mouth, (3) inability to move the neck, (4) gagging or resisting the use of the laryngoscope, and (5) oral injuries.
Apnea is the major contraindication to blind nasotracheal intubation. Attempts to place the tube without respirations as a guide are futile. Relative contraindications include basilar skull fracture and nasal injury. Furthermore, significant bleeding may occur if the patient is receiving anticoagulants or has a coagulopathy. Blind nasotracheal intubation should be avoided in patients with expanding neck hematomas. Patient combativeness, if not controlled with sedation, is also a contraindication.
Some would argue that the inability to open the mouth is a relative contraindication, because emesis may be induced that could not be cleared. The operator must exercise judgment in the individual case and be prepared to use neuromuscular blocking agents or to bypass the upper airway with a surgical technique if such a complication develops.

Procedure
The patient is placed in the "sniffing" position with the proximal neck slightly flexed and the head extended on the neck. In preparation for intubation, the operator constricts the nasal mucosa of both nares, using either 0.25 to 1.0% phenylephrine drops, oxymetazoline (Afrin) spray, or 4% cocaine spray. Topical anesthesia of the nares, oropharynx, and hypopharynx with lidocaine spray (10%) is also indicated if time permits. If available, cocaine is ideal because it is both a vasoconstrictor and an anesthetic; caution is necessary in hypertensive patients. The most patent nostril is chosen. In the cooperative patient, this can be determined simply by occluding each nostril and asking the patient which one is easier to breathe through. The most patent nostril can also be identified by direct vision, or by gently inserting a gloved finger lubricated with viscous lidocaine, full length into the nostrils. If time is not an issue, an effective method to dilate the nasal cavity and administer the anesthetic is to pass a lidocaine gel-lubricated nasopharyngeal airway (nasal trumpet) into the selected nostril. This
airway is left in place for several minutes, and progressively larger trumpets are introduced.
After preparation of the nostril, a well-lubricated endotracheal tube with a 7.0 or 7.5 mm ID is inserted along the floor of the nasal cavity. The tube is not directed cephalad, as one might expect from the external nasal anatomy, but rather is directed straight back toward the occiput, corresponding with the nasal floor. Twisting the tube may help bypass soft tissue obstruction in the nasal cavity. It is sometimes recommended that the bevel of the tube be oriented toward the septum to avoid injury to the inferior turbinate. However, such an event is rare. At 6 to 7 cm, one usually feels a "give" as the tube passes the nasal choana and negotiates the abrupt 90° curve required to enter the nasopharynx. This is the most painful and traumatic part of the procedure and must be done gently. If resistance is encountered that persists despite continued gentle pressure and twisting of the tube, the passage of a suction catheter down the tube and into the oropharynx may allow for successful passage of the tube over the catheter. [44] If this fails, the other nostril should be tried. In an attempt to avoid this difficulty from the outset, a controllable-tip tracheal tube (Endotrol, Mallinckrodt Medical Inc, St Louis) may be used that allows the operator to increase the flexion of the tube and facilitates passage past this tight curve. One study found the Endotrol tube to enhance first attempt success with blind nasotracheal intubation.
As the tube is advanced through the oropharynx and hypopharynx and approaches the vocal cords, breath sounds from the tube become louder, and fogging of the tube may occur. At the point of maximal breath sounds, the tube is lying immediately in front of the laryngeal inlet. The tube is most easily advanced into the trachea during inspiration because that is when the vocal cords are maximally open. As the patient begins to breathe in, the tube is advanced in one smooth motion. If a gag reflex is present, the patient usually coughs and becomes stridulous during this maneuver, suggesting successful tracheal intubation. The absence of such a response should alert the operator to probable esophageal passage. If there is a delay in advancing the tube, oxygen can be added to the end of the tube to increase inspired oxygen. Once the tube is in the trachea, moaning and groaning should cease. If they continue, esophageal intubation is likely. Breath sounds coming from the tube and tube fogging are other signs of endotracheal placement. Reflex swallowing during blind nasotracheal intubation may direct the tube posteriorly toward the esophagus. If this occurs, the conscious patient should be directed to stick out the tongue to inhibit swallowing and prevent consequent movement of the larynx. Application of laryngeal pressure may also help avoid esophageal passage.
Following intubation, both lungs are auscultated while positive-pressure ventilation is applied. If only one lung is being ventilated, the tube is withdrawn until breath sounds are heard bilaterally. The optimum distance from the external nares to the tube tip is about 28 cm in males and 26 cm in females. After verification of tracheal placement, the cuff is inflated and the tube is secured.

Technical Difficulties
The nasotracheal tube may slide smoothly through the hypopharynx and into the trachea on the first pass. Unfortunately, this is not always the case; in the operating room, the first attempt was successful in <50% of cases. When the initial pass is unsuccessful, there are 4 potential locations of the tip of the tube: (1) anterior to the epiglottis in the vallecula, (2) on the arytenoid or vocal cord, (3) in the piriform sinuses, or (4) in the esophagus.
Observation and palpation of the soft tissues of the neck during attempted passage of the nasotracheal tube are helpful in determining the location of the misplaced tube. This is ideally done by the operator but may also be performed by an experienced attendant. Before reattempting placement, the tube is withdrawn slightly; it is not removed from the nose, because this will create additional trauma to the nasal soft tissues. The possibility of cervical spine injury must be kept in mind when considering corrective maneuvers. Any maneuver that moves the neck significantly should not be used if alternatives are available. Methods for achieving success when difficulties with tube placement are encountered include the following:

Anterior to the epiglottis.
Difficulty advancing the tube beyond 15 cm or palpation of the tube tip anteriorly at the level of the hyoid bone suggests an impasse anterior to the epiglottis in the vallecula. Withdrawing the tube 2 cm, decreasing the degree of neck extension, and readvancing the tube will frequently remedy this problem.

Arytenoid cartilage and vocal cord.
Contrary to the classic teaching, recent studies have demonstrated a propensity for a nasotracheal tube, when placed through the right nares, to lie posteriorly and to the right as it approaches the larynx. It is not surprising, then, that the most common obstacles to advancement of the nasotracheal tube are the right arytenoid and vocal cord. No data are available on the common obstacles encountered if the tube is placed in the left nares. If the tube appears to be hanging up on firm, cartilaginous tissue, withdraw the tube 2 cm, rotate it 90° counterclockwise, and readvance the tube. This maneuver orients the bevel of the tube posteriorly and frequently results in successful passage . Another technique is to pass a suction catheter down the tube; it often will pass through the larynx without difficulty and the tube can then be advanced over the catheter.

Piriform sinus.
Bulging of the neck lateral and superior to the larynx indicates tube location in a piriform sinus. The tube should be withdrawn 2 cm, rotated slightly away from the bulge, and readvanced. An alternate method is to tilt the patient's head toward the side of the misplacement and reattempt placement.

Esophageal placement.
Esophageal placement is indicated by a smooth passage of the tube with the loss of breath sounds. The larynx may be seen or felt to elevate as the tube passes under it. Assisted ventilation will usually produce gurgling sounds when the epigastrium is auscultated. The tube should be withdrawn until breath sounds are clearly heard, and passage should be reattempted while pressure is applied to the cricoid. Increased extension of the head on the neck during placement may help. If attempts continue to result in esophageal misplacement, the following maneuver may result in successful tracheal intubation: from the precise point at which breath sounds are lost, the endotracheal tube is withdrawn 1 cm. The cuff is inflated with 15 mm of air, resulting in an elevation of the tube off the posterior pharyngeal wall and angling it toward the larynx. The tube is then advanced 2 cm; continued breath sounds indicate probable intralaryngeal location. At this point, the cuff is deflated and the endotracheal tube is advanced into the trachea . This technique may be particularly useful in the patient with cervical spine injury, because it requires no manipulation of the head or neck. This maneuver, when used on the first pass in 20 patients in the operating room, was successful in 75% of cases. One should bear in mind, however, that these patients were paralyzed and thus did not experience the laryngospasm that may be encountered in a breathing patient. The use of topical anesthesia is recommended. Alternatively, if a controllable-tip endotracheal tube (Endotrol) is used, the tip can be flexed anteriorly to help avoid esophageal placement. Remember that the tip is very responsive to pulling on the ring. A common mistake is to exert too much force on the ring, resulting in the tube curling up short of the larynx, thus preventing tube advancement.

Laryngospasm.
Laryngospasm is common when attempting nasotracheal intubation. It is usually transient. The tube is withdrawn slightly and the operator should wait for the patient's first gasp; advancement of the tube at this precise moment is frequently successful, as the vocal cords are widely abducted during forced inhalation. Laryngeal anesthesia should also be assessed, and if IV and nebulized lidocaine have already been administered without success, transcricothyroid anesthesia (e.g., 2 mL of 4% lidocaine) should be considered. Occasionally, a jaw lift is necessary to break prolonged spasm. Another option is to use a smaller tube.

Placement Under Direct Vision
This technique combines elements of oral and nasotracheal intubation. The indications and precautions are similar, and the importance of considering cervical spine injury is identical. Likewise, the need for jaw opening by physical or pharmacologic means is unchanged. This method is preferred to orotracheal intubation if the presence of an orotracheal tube might interfere with the repair of an oral injury. It is also useful when blind nasotracheal intubation has failed.
Preparation of the nose and nasopharynx and passage of the tube into the oropharynx are the same as described for blind nasotracheal intubation. It is with the introduction of the laryngoscope that the technique changes.
Laryngoscopy, as described with orotracheal intubation, is used to visualize the vocal cords and the tip of the endotracheal tube. With the Magill forceps in the right hand, the endotracheal tube is grasped proximal to the cuff (to avoid damage to the balloon) and directed toward the larynx . An assistant advances the tube gently while the operator directs the tip into the larynx and trachea. Cricoid pressure may facilitate the passage. Often the larynx can be manipulated sufficiently with the laryngoscope so that the physician can advance the tube with the right hand and guide it between the cords without using the Magill forceps. Occasionally, the natural curve of the tracheal tube guides it through the cords without any manipulation. The cuff is inflated, and both lungs are auscultated to ensure ventilation. When placement is satisfactory, the tube is secured.

Complications
Epistaxis is the most common complication of nasotracheal intubation. However severe epistaxis was encountered in only 5 of 300 cases reported by Danzl and Thomas. [42] Tintinalli and Claffey reported severe bleeding in 1 of 71 cases and less serious bleeding in 12 others. [54] Bleeding is usually not a problem unless it provokes vomiting or aspiration, a serious potential problem in obtunded patients with a clenched jaw or a decreased gag reflex. Other immediate complications include turbinate fracture, intracranial placement through basilar skull fracture, retropharyngeal laceration or dissection, and delayed or unsuccessful placement. Unsuccessful placement may be minimized by selection of a smaller tube and by gentle technique.
Sinusitis in patients with nasotracheal tubes is common and can be an unrecognized cause of sepsis. Rare but potentially fatal delayed complications include mediastinitis following retropharyngeal abscess and massive pneumocephalus.
Because most of the complications occur during tube advancement through the nasal passage and proximal nasopharynx, the complications of blind nasotracheal intubation and placement under direct vision are largely the same. However, retropharyngeal laceration and esophageal intubation are more of a threat in blind placement techniques because they are more likely to go unrecognized. One unique problem associated with nasotracheal intubation is damage of the tube cuff with the Magill forceps.
Delayed nasotracheal placement under direct vision deserves special discussion. Manipulation of the endotracheal tube through the nose and with the Magill forceps during the direct vision technique involves additional steps that require time. Because time is of the essence in the resuscitation of the critically ill patient, orotracheal intubation may be preferable.

Summary
Nasotracheal intubation is being used less frequently than in the past, because practitioners are increasingly comfortable using oral intubation in the patient with potential cervical spine injury. In addition, emergency physicians frequently use paralytics to facilitate orotracheal intubation. Nevertheless, nasotracheal intubation remains an effective and potentially life saving approach to the difficult airway and should be a dependable part of the armamentarium of all providers who are active in emergency airway management.

MODIFIED OROTRACHEAL INTUBATION

Intubation with an Intermediate Airway in Place
Esophageal Obturator/Gastric Tube Airway in Place
The unconscious patient who requires ventilatory assistance may benefit from the temporary use of the esophageal obturator airway (EOA) or similar device. Although this may be an effective means of ventilation, it is at best a temporary measure. The patient experiencing upper airway hemorrhage with the EOA in place may have oropharyngeal blood insufflated into the trachea. Also, an endotracheal tube is the preferred airway, because with endotracheal intubation the airway is more secure and ventilation more convenient. Although the EOA may allow rapid airway support until cervical spine injury can be ruled out, it is recommended that the EOA not be left in place for more than 2 hours.
Replacement of the EOA with an orotracheal tube requires appropriate care. Removal of the esophageal cuff before placement of the endotracheal tube is fraught with danger. Spontaneous gastric regurgitation often occurs on EOA removal. The rescuer must therefore learn to perform endotracheal intubation around the EOA to protect the patient from aspiration.
The patient is hyperventilated through the EOA before intubation is attempted around it. The EOA mask is then removed, and the EOA tube is moved to the left side of the patient's mouth. Laryngoscopy and intubation are then performed in the usual fashion. If resistance to passage of the tracheal tube is met, the volume of the EOA balloon should be reduced, because the balloon may be producing distortion of the larynx. Next, the operator deflates the EOA balloon completely and slides it out of the patient's esophagus. If resistance is met, the operator must be sure that the esophageal cuff has been deflated completely.

Esophageal-Tracheal Combitube (ETC) in Place
Combitubes placed in the esophagus will generally require replacement with a tracheal tube. The inflated pharyngeal balloon prevents tracheal intubation around this airway. This proximal balloon must be deflated before attempting tracheal intubation. If intubation is still not possible, the ETC may need to be removed; the stomach should first be emptied via a gastric tube placed through the esophageal port of the airway. Suction is readied, the distal balloon is deflated, and the patient is quickly intubated. This maneuver poses an added risk over that associated with the esophageal obturator intermediate airway placement (i.e., EOA and EGTA) .

Laryngeal Mask Airway in Place
The trachea can often be intubated with the laryngeal mask airway (LMA) left in place.

Bullard Laryngoscope Use
A recent development for intubating the difficult airway is the Bullard laryngoscope, an anatomically shaped rigid fiberoptic laryngoscope that provides an indirect view of the larynx . It was design`ed to aid in intubating the difficult airway; and because no manipulation of the neck is necessary, it is especially well suited for the patient with potential cervical spine injury. Indeed, in the anesthetized patient, the Bullard laryngoscope has been found to cause less head extension and cervical spine extension than conventional laryngoscopes do. [36] The recent addition of an intubating stylet attached to the laryngoscope has resulted in increased ease and speed of intubation, and the technique appears to be effective regardless of the patient's head and neck anatomy. [37] Because alignment of the oropharyngeal and laryngeal axes is not required, the Bullard laryngoscope offers the advantage provided by a conventional fiberoptic scope but requires less training to gain proficiency in its use. [38]

Indications and Contraindications
The Bullard laryngoscope is indicated in patients with anticipated difficult airways who require definitive airway control. It can be used in awake as well as unresponsive patients. [39] The total inability to open the mouth is a contraindication to the use of this laryngoscope. However, because the Bullard laryngoscope follows the contour of the mouth and hypopharynx, only 2 cm of occlusal opening is necessary for the introduction of the scope plus endotracheal tube for intubation.

Procedure
The technique for introducing the Bullard laryngoscope blade is similar to that for direct laryngoscopy. The operator, who is at the head of the patient, opens the mouth with the left thumb while holding the head stable. As the scope blade is introduced into the oropharynx, the handle is rotated to follow the curve of the hypopharynx until the handle is fully vertical. The tip of the blade can be used to lift the epiglottis, but visualization of the larynx is usually possible without this maneuver. Only minimal force is exerted along the axis of the handle. Intubation of the larynx can be accomplished using a styletted endotracheal tube or an endotracheal tube with a directional tip (Endotrol; Mallinckrodt, Critical Care, Glens Falls, NY). The technique is generally successful when using the new Bullard intubating stylet. [37]
Awake intubation using the Bullard laryngoscope can be performed comfortably using topical anesthesia and light IV sedation. [39] Adult and pediatric Bullard laryngoscopes are available, and the scope has been used successfully in neonates. [38] The Bullard scope can also be used in conjunction with nasotracheal intubation and has the advantage of requiring only 6 mm of mouth opening through which to insert the blade. [40]

Complications
The major difficulty in using the Bullard laryngoscope is the inability to visualize the larynx because of blood, emesis, or secretions. Another reason for failure is the inability to place the blade tip under the epiglottis. [37]

Summary
The Bullard scope is useful in the difficult airway uncomplicated by blood and excessive secretions. In the all-too-common setting of blood and secretions, however, the inability to visualize the vocal cords significantly limits the utility of this device in emergency airway management.

OROTRACHEAL INTUBATION

Indications and Contraindications
Any clinical situation in which a definitive airway is necessary and limited neck motion is permissible is an indication for orotracheal intubation. Many of these situations, including cardiac arrest, airway compromise in infection and trauma, and airway obstruction are discussed in detail in Chapter 1 . Most orotracheal intubations are accomplished using a direct laryngoscope. An unstable cervical spine injury is a relative contraindication to direct laryngoscopy.

Equipment
Laryngoscope
Facility in the use of the direct laryngoscope is a prerequisite for orotracheal intubation. Various adult and pediatric blade sizes are available. There are two basic blade designs-- curved (MacIntosh) and straight (Miller and Wisconsin). Slight variations in laryngoscopic technique follow from one's choice of blade design, which is often a matter of personal preference. The tip of the straight blade goes under the epiglottis and lifts it directly, whereas the curved blade fits into the vallecula and indirectly lifts the epiglottis via the hyoepiglottic ligament to expose the larynx. Special blades designed for the anterior larynx include the Siker and the Belscope (Avulunga Pty Ltd, New South Wales, Australia).
Each blade type has advantages and disadvantages. The straight blade is usually a better choice in pediatric patients, in patients with an anterior larynx or a long floppy epiglottis, and in individuals whose larynx is fixed by scar tissue. It is less effective, however, in patients with prominent upper teeth, and it is more likely to break teeth. Use of the straight blade is also more often associated with laryngospasm due to its stimulation of the superior laryngeal nerve, which innervates the undersurface of the epiglottis. A straight blade may inadvertently be advanced into the esophagus and initially present one with unfamiliar anatomy until it is withdrawn. The blade has a light bulb at the tip that may slightly hamper vision. The wider, curved blades are helpful in keeping the tongue retracted from the field of vision, allowing for more room in passing the tube in the oropharynx, and they are generally preferred in uncomplicated adult intubations. Aside from patient considerations, some clinicians prefer the curved blade because they find it requires less forearm strength than the straight blade.

Tracheal Tubes
The standard endotracheal tube is plastic and measures approximately 30 cm. Tube sizing is based on internal diameter (ID), measured in millimeters, and ranges from a 2.0 to a 20.0 mm tube, increasing in increments of 0.5 mm. The outer tube diameter is 2 and 4 mm larger than the internal diameter. Tube size is printed on the tube. There is also a scale, in centimeters, for determining the distance along the tube from the tip.
Adult men will generally accept a 7.5 to 9.0 mm orotracheal tube, whereas women can usually be intubated with a 7.0 to 8.0 mm tube. In most circumstances, tubes smaller than these should not be used, especially in patients with chronic obstructive lung disease who may be difficult to wean from the respirator due to excessive airway resistance from a small tube. However, in emergency intubations, particularly if a difficult intubation is anticipated, many clinicians
choose a smaller tube and change to a larger tube later if necessary. One exception is in the burn patient, in whom one places as large a tube as possible on the initial attempt because swelling may prohibit subsequent tube placement. For nasal intubation, a slightly smaller tube (by 0.5 to 1.0 mm) is chosen.
The cuff of a standard tracheal tube is high-volume and low-pressure. A clinical test for determining correct cuff inflation is to slowly inject air until no air leak is audible while the patient is receiving bag-tube ventilation. This usually occurs with 5 to 8 mL of air if the proper-sized tracheal tube has been selected. Many clinicians use the tension of the pilot balloon as a guide to cuff inflation; slight compressibility with gentle external pressure indicates adequate inflation for most clinical situations. For long-term use, cuff pressure should be measured and maintained at 20 to 25 mm Hg. Capillary blood flow is compromised in the tracheal mucosa when the cuff pressure exceeds 30 mm Hg.
In infants and children, the following formula is a highly accurate method for determining correct tracheal tube size:

Tube size = [4 + age (years)]/4

For most clinical situations, however, using the width of the nail of the little finger as a guide is sufficiently accurate and has been shown to be more precise than finger diameter 45911.
Correct tube size is especially important in the pediatric population, because most patients younger than 8 years are intubated with an uncuffed tube; adequate tube size is necessary to provide a good seal between the tube and the upper trachea and to prevent aspiration. A cuffed tube is used in children with decreased lung compliance who may require prolonged mechanical ventilation. In a child, the smallest airway diameter is at the cricoid ring rather than at the vocal cords, as in adults. Hence, a tube may pass the cords but go no farther. Should this occur, the next smaller sized tube should be passed after reoxygenation.
Adult endotracheal tubes will accept a standard adaptor on which the ventilator tubing will fit. Pediatric tubes require a special adaptor with a distal end small enough to accommodate the small tube size.

Preparing for Intubation
Before beginning intubation, a number of issues should be addressed. In chronologic order, they are (1) confirm that
the required intubation equipment is available and functioning; (2) position the patient correctly; (3) assess the patient for difficult airway; (4) establish intravenous (IV) access, time permitting; (5) draw up essential drugs, and; (6) attach the necessary monitoring devices. In the haste of the moment, it is a common error to fail to position the patient properly or to proceed with the procedure before the proper equipment is assembled and checked. Simple omissions, such as failing to restrain the patient's hands, removing dentures, or misplacing the suction device, can seriously hamper the performance of the procedure. A suggested pre-intubation checklist is presented in Table 2-2 .
In addition to the preparation necessary for optimum patient care, the operator should also minimize exposure to potentially infectious materials . Generally, the operator should be gloved and should wear eye and mouth protection to guard against exposure to patient secretions.
The endotracheal tube cuff should be checked for leaks by inflating the balloon before attempting intubation. The tube is prepared for placement by passing a flexible stylet down the tube to increase its stiffness and enhance control of the tip of the tube. The stylet should not extend beyond the end of the tube. The tube is then bent in a gradual curve with a more acute angling in the distal one-third to more easily access the anterior larynx. The tip and cuff of the tube are lubricated with viscous lidocaine or another water-soluble gel.
The patient should be positioned to optimally align the oral, pharyngeal, and laryngeal axes . The desired position was aptly described by Magill to make the patient appear to be "sniffing the morning air," with the head extended on the neck and the neck slightly flexed relative to the torso. A small towel under the occiput (to raise it 7 to 10 cm) may facilitate positioning. Positioning of the head and neck is a critical step; nonoptimal head positioning may be the sole reason for some intubation failures.

The Difficult Airway
The majority of difficult intubations are predictable. Perhaps the most frequently encountered condition associated with a difficult intubation is the agitated or combative patient. Fortunately, this condition can be readily eliminated through pharmacologic intervention. The classic parameters that predict a difficult intubation include a history of previous difficult intubation, prominent upper incisors, limited ability to extend at the atlanto-occipital joint, [5] poor visibility of pharyngeal structures when the patient extends the tongue (Mallampati's classification, or the tongue/pharyngeal ratio), [6] limited ability to open the mouth, [7] a limited direct laryngoscopic view of the laryngeal inlet, [7] and a short distance from the thyroid notch to the chin with the neck in extension . [8] Radiographic indicators of the ease of intubation include the mandibular length-to-height ratio [9] and the distance from the spine of the atlas to the occiput. [10] In emergency airway management, many of these predictors are not obtainable. An extensive history is rarely available, the patients are frequently uncooperative, and the presence of trauma limits movement of the neck. Fortunately, some of the key predictors are apparent simply by observing the external appearance of the patient's head and neck.
Patients with neck tumors, thermal or chemical burns, traumatic injuries to the face and anterior neck, angioedema and infection of the pharyngeal and laryngeal soft tissues, or previous operations in or around the airway suggest a difficult intubation because distorted anatomy or secretions may compromise visualization of the vocal cords. Facial or skull fractures may further limit airway options by precluding nasotracheal intubation. Patients with ankylosing arthritis or developmental abnormalities, such as a hypoplastic mandible or the large tongue of Down's syndrome, are difficult to intubate because neck rigidity and problems of tongue displacement can obscure visualization of the glottis.
Besides these obvious congenital and pathologic conditions, the short, thick neck poses the greatest difficulty for performing orotracheal intubation. In such individuals, the larynx is anatomically higher and more anterior, which makes it harder to visualize the vocal cords. These individuals are easily identified by observing the head and neck in profile. In such patients, apply laryngeal pressure and consider using the straight blade. Use of other options, including nasotracheal intubation, may be required.
It should be emphasized that some patients, despite normal-appearing anatomy and the absence of a complicating history, are unexpectedly difficult to intubate. One must be prepared for this rare but inevitable occurrence.

Procedure

Adults

Direct laryngoscopy.
The operator is stationed at the patient's head . The patient is generally supine with the head at the level of the operator's lower sternum. To maintain the best mechanical advantage, the operator keeps his or her back straight and does not hunch over the patient; any bending should occur in the knees. The left elbow is kept relatively close to the body and flexed to provide better support. In the severely dyspneic patient who cannot tolerate lying down, direct laryngoscopy can be performed with the patient seated semi-erect and the laryngoscopist on a stepstool behind the patient. [11]
The laryngoscope is grasped in the left hand with the blade directed toward the patient from the hypothenar aspect of the operator's hand. The patient's lower lip is drawn down with the right thumb, and the tip of the laryngoscope is introduced into the right side of the mouth. The blade is slid along the right side of the tongue, gradually displacing the tongue toward the left as the blade is moved to the center of the mouth. If the blade is initially placed in the middle of the tongue, the tongue will fold over the lateral edge of the blade and obscure the airway. Placing the blade in the middle of the tongue and failure to move the tongue to the left are two common errors preventing visualization of the vocal cords.
As the blade tip approaches the base of the tongue, the operator exerts a force along the axis of the laryngoscope handle, lifting upward and forward at a 45° angle. The epiglottis should come into view with this maneuver. It may help to have an assistant retract the cheek laterally to further expose the laryngeal structures. Do not bend the wrist; bending the wrist can result in dental injury because the teeth may be used as a fulcrum for the blade.
The step following visualization of the epiglottis depends on which laryngoscope blade is used. With the curved blade, the tip is placed into the vallecula, the space between the base of the tongue and the epiglottis. Continued anterior elevation of the base of the tongue and the epiglottis will expose the vocal cords. If the blade tip is inserted too deeply into the vallecula, the epiglottis may be pushed down to obscure the glottis. [6] When using the straight blade, the tip is inserted under and slightly beyond the epiglottis, directly lifting this structure. The jaw and larynx are literally suspended by the blade. If the straight blade is placed too deeply, the entire larynx may be elevated anteriorly and out of the field of vision. Gradual withdrawal of the blade should allow the laryngeal inlet to drop down into view. If the blade is deep and posterior, the lack of recognizable structures indicates esophageal passage; gradual withdrawal should permit the laryngeal inlet to come into view.
Proper neck positioning and pressure (cephalad, dorsally, and rightward) on the larynx by an assistant will facilitate visualization and intubation of an anterior larynx. If needed, suctioning is performed at this point. If the vocal cords are still not seen, consider using a tracheal tube introducer (Smiths Industries Medical Systems, Keene, NH). This device, also known as the "elastic gum bougie," is a long, semirigid introducer that is placed, using the laryngoscope, through the laryngeal inlet and into the trachea. [12A] The tracheal tube is then passed over the introducer and the introducer is withdrawn. If resistance is met in passing the tracheal tube, rotate the tube 90° counterclockwise and advance the tube.

Tube passage.
Once the vocal cords have been visualized, the final and most important step, tube passage under direct vision through the vocal cords and into the trachea, is performed. The tube is held in the operator's right hand and introduced from the right side of the patient's mouth. The tube is advanced toward the patient's larynx at an angle, not parallel with or down the slot of the laryngoscope blade. This way, the operator's view of the larynx is not obstructed by the hand or the tube until the last possible moment before the tube enters the larynx. The tube should be passed during inspiration, when the vocal cords are maximally open. It enters the trachea when the cuff disappears through the vocal cords. The tube is advanced 3 to 4 cm beyond this point. It is not enough to see the tube and the cords; the tube must be seen passing through the vocal cords to ensure tracheal placement.
When the vocal cords are stimulated, laryngospasm-- the persistent contraction of the adductor muscles of the vocal cords--may prevent passage of the tube. Inadequate anesthesia is often the cause. Pretreatment with topical lidocaine decreases the likelihood of this occurring. Two percent or 4lidocaine is sprayed directly on the cords. An infrequent but effective route for achieving tracheal anesthesia is via transtracheal puncture, injecting a bolus of 3 to 4 mL of lidocaine through the cricothyroid membrane. Laryngospasm is usually brief and is often followed by a gasp. The operator should be ready to pass the tube at this moment. Occasionally, the spasm is prolonged and needs to be broken with sustained anterior traction applied at the angles of the mandible--the jaw lift. At no time should the tube be forced, because permanent damage to the vocal cords may result. Consideration should be given to using a smaller tube. Prolonged, intense spasm may ultimately require muscle relaxation with a paralyzing drug . The pediatric patient is far more prone to laryngospasm than is an adult. [12] In a child, if vocal cord spasm prevents tube passage, a chest thrust maneuver may momentarily open the passage and permit intubation.

Positioning and securing the tube.
The endotracheal tube should be secured in a position that minimizes both the chance of inadvertent endobronchial intubation and the risk of extubation. The tip should lie in the midtrachea with room to accommodate neck movement. Because tube movement with both neck flexion and extension averages 2 cm, the desired range of tip location is between 3 and 7 cm above the carina. [14]
On a radiograph, the tip of the tube should ideally be 5 ± 2 cm above the carina when the head and neck are in a neutral position. On a portable radiograph, the adult carina overlies the fifth, sixth, or seventh thoracic vertebral body. If the carina is not visible, it can be assumed that the tip of the tube is properly positioned if it is aligned with the T3 or T4 vertebra. In children, the carina is more cephalad than in the adult, but it is consistently situated between T3 and T5. In children, T1 is used as the reference point for the tip of the endotracheal tube. [15]
An estimate of the proper depth of tube placement can be derived from the following formulas, the lengths representing the distance from the tube tip to the upper incisors in children and from the upper incisors [18] or the corner of the mouth [19] in adults:
Adults: Tracheal tube depth (cm) = 21 cm (women)
Tracheal tube depth (cm) = 23 cm (men)
In adults, this method has been shown to be more reliable than auscultation in determining the correct depth of placement. [18]
The cuff is inflated to the point of minimal air leak with positive-pressure ventilation. In an emergency intubation, 10 mL of air is placed in the cuff, and inflation volume is adjusted after the patient's condition is stabilized.
After tracheal tube placement, both lungs are auscultated under positive-pressure ventilation. Care is taken to auscultate laterally because midline auscultation may lead to an erroneous impression of tracheal placement when the tube is actually in the esophagus. With the tube in position and the cuff inflated, the tube is secured in place. Commercial endotracheal tube holders, adhesive tape, or umbilical (nonadhesive cloth) tape can be attached securely to the tube and around the patient's head . The tube should be positioned in the corner of the mouth, where the tongue cannot expel it. This position is also more comfortable for the patient and allows for suctioning. A bite-block or oral airway to prevent endotracheal tube crimping or damage from biting is commonly incorporated into the system used to secure the tube.

Infants and Children
Appreciation of the anatomic differences between children and adults is helpful when intubating the pediatric patient . Infants' proportionately larger head naturally places them in the "sniffing position," so a towel under the occiput is rarely necessary. The large head can even result in a posterior positioning of the larynx that prevents visualization of the vocal cords; a small towel under the child's shoulders should correct this problem. The head also may be floppy, and it can be stabilized by an assistant during intubation. The child's increased tongue-to-oropharynx ratio and shorter neck hinder forward displacement of the tongue and, coupled with a long U-shaped epiglottis, can make visualization of the glottis difficult.
Consequently, direct laryngoscopy in the infant and young child is generally best performed with a straight blade: Miller size 0 for premature infants, size 1 for normal-sized infants, and size 2 for older children. The infant's larynx lies higher and relatively more anterior. One can have an assistant lightly apply laryngeal pressure, or the operator can use the little finger of the hand holding the laryngoscope blade for this purpose . If no laryngeal structures are visible after laryngeal pressure, the blade should be gradually withdrawn, because inadvertent advancement of the blade into the esophagus is a common error.

Confirmation of Tracheal Intubation

Clinical Assessment
The best assurance of tracheal placement is for the operator to see the tube pass through the vocal cords . Absent or diminished breath sounds, vocalization, increased abdominal size, and gurgling sounds during ventilation are clinical signs of esophageal placement. However, esophageal placement is not always obvious. One may hear "normal" breath sounds if only the midline of the thorax is auscultated. One way to clinically assess tracheal placement after a ventilation or during spontaneous respiration is to note whether air is felt or heard to exit through the tube following cuff inflation. If the tidal volume is adequate, the exit of air should be obvious. It is important to note that when an appropriately sized tube is placed in the trachea, the patient cannot groan, moan, or speak. Any vocalization suggests esophageal placement.
Asymmetrical breath sounds indicate probable main stem bronchus intubation. Due to the angles of takeoff of the main bronchi and the fact that the carina lies to the left of the midline in adults, right main stem intubation is most common and is indicated by decreased breath sounds on the left side. When asymmetrical sounds are heard, the cuff should be deflated and the tube withdrawn until equal breath sounds are present. Bloch and colleagues report accurate pediatric tracheal positioning if after noting asymmetrical breath sounds, the tube is withdrawn a defined distance beyond the point at which equal breath sounds are first heard--2 cm in children younger than 5 years and 3 cm in older children. [20]

Esophageal Detector Device
An aspiration technique used to determine endotracheal tube location was first described by Wee in 1988. [21] The technique takes advantage of the difference in tracheal and esophageal resistance to collapse during aspiration to determine location of the tip of the tracheal tube. Following intubation, a large syringe is attached to the end of the endotracheal tube and the syringe plunger is withdrawn. If the tube is correctly placed in the trachea, the plunger will pull back without resistance as air is aspirated from the lungs. However, if the tracheal tube is in the esophagus, resistance is felt when the plunger is withdrawn, because the pliable walls of the esophagus collapse under the negative pressure and occlude the end of the tube. Another device using the same principle as syringe aspiration is the self-inflating bulb (e.g., Ellick's device).
Wee first reported use of an esophageal detector device in the operating room. [21] The tube was correctly identified in 99 of 100 cases (51 esophageal, 48 tracheal). The device result was considered equivocal in the remaining tracheal tube. The tube was removed and found to be nearly totally occluded with purulent secretions. Slight resistance was noted in one patient with a right main stem intubation; resistance decreased when the tube was pulled back. Before use, the esophageal detector device must always be checked for air leaks. If any connections are loose, the leak may allow the syringe to be easily withdrawn, mimicking tracheal location of the tube.
Wee recommends the following guidelines in using the aspiration technique: apply constant, slow aspiration to avoid tube occlusion from tracheal mucosa drawn up under high negative pressure. If the tracheal tube is correctly placed, 30 to 40 mL of air can be aspirated without resistance. If air was initially aspirated and then some resistance is encountered, the tracheal tube should be pulled back between 0.5 and 1.0 cm and partially rotated. This takes the tube out of the bronchus, if it has been placed too deeply, and changes the orientation of the bevel if the tube has been temporarily occluded with tracheal mucosa. Air is easily aspirated if the tube was in the trachea, but repositioning will make no difference if the tube was in the esophagus. The syringe aspiration technique can be used before or after ventilation of the patient. Continuous cricoid pressure should be applied pending tube confirmation. Inflation of the tube cuff will have no effect on the reliability of the test. [22] This device is reliable, rapid, inexpensive, and easy to use. Jenkins reported good success with physician use of the aspiration technique to confirm placement of emergency department and out-of-hospital intubations. [23]
A squeeze-bulb aspirator can be used as an alternative to the syringe technique. [24] [25] The bulb is attached to the endotracheal tube and squeezed; if the tube is in the esophagus, it is often accompanied by a flatus-like sound followed by absent or markedly delayed refilling. Insufflation of a tube in the trachea is silent, with instantaneous refill. An early study with the Ellick's evacuator bulb device reported that 87% of esophageal tubes were identified. [24] A later study using a slightly different bulb device (Respironics, Murrysville,Pa) found that all 45 esophageal tubes were detected. [25] The device is cheap and easy to use and can be operated single-handedly in <5 style="font-weight: bold;">End-Tidal CO2 Detector Devices
A high level of CO2 in exhaled gas is the physiologic basis for capnography and the principle on which end-tidal CO2 (ETCO2 ) detectors was developed. The most commonly available devices for emergency use are colorimetric indicators responding to CO2 levels of gas flowing through the device when placed on the tracheal tube adapter. The typical device displays two extreme colors indicating a low level of CO2 in esophageal intubation and another color in tracheal intubation. An intermediate color is indeterminate. Hand-held quantitative or semiquantitative electronic CO2 monitors are also available.
A multicenter study of a colorimetric device demonstrated an overall sensitivity of 80% and a specificity of 96%. [26] In patients with spontaneous circulation and the tracheal tube cuff inflated, the sensitivity and specificity rose to 100%. The poor sensitivity seen in cardiac arrest (69%) is due to the fact that low exhaled CO2 levels are seen in both very-low-flow states and in esophageal intubation. The device must therefore be used with caution in the cardiac arrest victim. Levels of CO2 return to normal after return of spontaneous circulation in these patients. Further, colorimetric changes may be difficult to discern in reduced lighting situations, and secretions can interfere with the color change. Regardless of the monitoring device, patients in cardiac arrest should be ventilated for a minimum of 6 breaths prior to taking a reading, because recent ingestion of carbonated beverages can result in spuriously high CO2 levels with esophageal intubation. [27]

Comparison of Detector Devices
In the setting of spontaneous circulation, both syringe aspiration and ETCO2 detection are highly reliable means of excluding esophageal intubation. A comparison of the techniques with clinical assessment was carried out in the animal laboratory, with measurement of the speed and accuracy of determination of tube placement. [28] Both the syringe esophageal detector device and ETCO2 detection were highly accurate, approaching 100%. The esophageal detector device was more rapid with determination in 13.8 seconds vs 31.5 seconds for ETCO2 detection. The detector device remained accurate when air was insufflated into the esophagus for 1 minute, simulating unrecognized esophageal placement. Clinical assessment alone yielded an alarming 30% rate of misidentifying an esophageal tube as being in the trachea. In the setting of cardiac arrest, the aspiration method is more reliable than CO2 detection, because its accuracy is not dependent on the presence of blood flow.

Complications
Prolonged efforts to intubate may result not only in hypoxia but also in cardiac decompensation. Pharyngeal stimulation can produce profound bradycardia or asystole; when it is feasible, an assistant should view the cardiac monitor during intubation of a patient who has not suffered cardiac arrest. Atropine should be available to reverse vagal-induced bradycardia that may occur secondary to suctioning or laryngoscopy. Prolonged pharyngeal stimulation also may result in laryngospasm, bronchospasm, and apnea.
The maximum interval allowable for routine intubation of the apneic patient is 30 seconds. As a guide, one should limit the time of an intubation attempt to the amount of time a single deep breath can be held. This is especially important in a child, because the functional residual capacity of a child's lungs is less than that of an adult. Failure to achieve control within this time frame demands an interval of bag-valve-mask ventilation before intubation is attempted again. The use of preoxygenation to minimize hypoxia is strongly recommended. An oxygen saturation monitor can also be used to monitor explicitly for hypoxia. Assuming optimal preoxygenation of the patient to >98% O2 saturation, attempts at intubation should be halted until the patient is reoxygenated whenever the O2 saturation drops below 92%, equal to a PO2 of about 60 to 65 mm Hg. When ventilation is not achievable, irreversible brain damage can result within minutes. Therefore, the maximum interval allowable for conservative airway management maneuvers is about 3 minutes; one must then choose alternative methods .
One should check for loose or missing teeth before and after orotracheal intubation. Any avulsed teeth not found in the oral cavity warrant a postlaryngoscopy chest film to rule out aspiration of a tooth. Swallowed teeth are of no consequence. In a study of 366 patients, McGovern and coworkers found broken teeth to be the most common complication of laryngoscopy. [29] Laceration of the mucosa of the lips, especially the lower lip, may occur if adequate care is not taken. Tracheal or bronchial injuries are rare but serious, usually occurring in infants and the elderly as a result of decreased tissue elasticity. [30] Vomiting with aspiration of gastric contents is another serious complication that can occur during intubation.
The most devastating complication of tracheal intubation is unrecognized esophageal intubation. Assessment of tube position should be the first step in the emergency department evaluation of patients who have undergone out-of-hospital intubation. The best assurance of tracheal placement is for the operator to see the tube pass through the vocal cords. Techniques to assess tube placement are discussed earlier. Another method of reliably determining tracheal tube location uses the fiberoptic scope. Passage of the scope through the tube with visualization of tracheal rings confirms endotracheal placement as well as the position within the trachea. The placement of a lighted stylet down the tracheal tube and successful transtracheal illumination also reliably predicts tracheal positioning. [31]
A chest radiograph should be taken shortly after the intubation to confirm tube placement and position. Bissinger and coworkers noted that endobronchial intubation was clinically unrecognized without a chest film in 7% of out-of-hospital intubations. [32] In addition to hypoxia, delayed tube repositioning can lead to unilateral pulmonary edema. [33] Persistent asymmetrical breath sounds after appropriate tube positioning suggests unilateral pulmonary pathology (e.g., main stem bronchus obstruction, pneumothorax, or hemothorax).
If an endotracheal tube is removed from the esophagus, vomiting may occur. This should be anticipated and suction readied. Cricoid pressure should be applied during tube removal and maintained until intubation is successful. Alternatively, the first tube can be left in the esophagus to serve as temporary gastric venting until tracheal intubation is achieved.
A persistent air leak during ventilation usually means one of three things: (1) the cuff is leaking because of damage to the balloon, (2) the cuff is positioned above or between the vocal cords, or (3) the pilot balloon is leaking. If the cuff is leaking, the tracheal tube must be replaced (see Changing Tracheal Tubes). If the pilot balloon is determined to be leaking, however, this can usually be remedied without changing the tube. [34] An incompetent 1-way balloon valve can be fixed by placing a stopcock into the inflating valve. Reinflation of the cuff followed by shutting off the stopcock should solve the problem. If the leak involves the pilot balloon itself, or if the distal inflation tube has been inadvertently severed, cut off the defective part and slide a 20-ga catheter into the inflation tube. Then connect the stopcock to the catheter, inflate the cuff, and close the stopcock.
Tracheal stricture used to be a significant late complication of long-term intubation with low-volume high-pressure cuffs. The standard use of high-volume low-pressure cuffs has markedly decreased the incidence of this complication. [35] Tubes with high-pressure cuffs are obsolete and should be avoided.

Summary
Orotracheal intubation is the mainstay of definitive airway management. In the comatose patient, it is usually accomplished rapidly and without difficulty. The easy intubation is frequently successful in the hands of the novice; the difficult intubation often proves challenging even for the experienced operator. Rapid-sequence intubation has increased the use of orotracheal intubation as the first-line approach in a variety of clinical situations and settings (see Chapter 3) . Once the patient's breathing and protective reflexes are removed, however, the operator has the supreme responsibility of safely reestablishing them. A mastery of the technique of orotracheal intubation is essential.