Techniques

In every case, the anesthesiologist must attempt to determine whether mask ventilation and intubation will be possible if the patient is anesthetized and paralyzed. The usual intubation sequence includes the administration of a rapidly acting induction agent (e.g., thiopental), demonstration of adequate mask ventilation, and administration of a rapidly acting neuromuscular blocking agent (e.g., succinylcholine). The introduction of sevoflurane has made inhalational induction and intubation a reasonable alternative for selected adults and children. Preoxygenation of such routine patients is optional but strongly recommended because it provides an added margin of safety. Preoxygenation is essential when a rapid-sequence intubation is chosen because of a full-stomach situation or other propensity to aspiration (e.g., esophageal disease). In this situation, the neuromuscular blocker is administered with the induction agent, cricoid pressure (i.e., Sellick maneuver) is applied, and mask ventilation is not provided unless unsuccessful intubation necessitates it.

Before routine or rapid-sequence intravenous induction, the clinician must determine whether this is the best and safest way to intubate the patient. This determination is aided by the history and physical examination findings in conjunction with knowledge of the factors and syndromes that affect the airway. The critical point in the decision tree is the administration of muscle relaxants; the clinician must decide whether difficulties in ventilation result from factors that can be improved by the advent of paralysis or the patient should be awakened and intubated with a conscious technique. If there is sufficient doubt before induction with regard to the patient's airway, a conscious intubation with sedation and topicalization is indicated. Other clinical factors, including hemodynamic instability and severe intestinal obstruction, may influence the decision. In children, such an awake intubation usually is not possible except in newborns. However, a mask airway can usually be maintained in most difficult pediatric intubations.

Endotracheal Intubation During Anesthesia

After it has been decided that the patient can be safely anesthetized for intubation, a variety of methods can be used to achieve acceptable intubating conditions.

Anesthetics and Muscle Relaxants

For intravenous induction, a rapidly acting anesthetic is first administered (see Chapter 13 ). This is usually

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The most commonly employed relaxant for intubation is succinylcholine, but the nondepolarizing relaxants in appropriate doses also may be used. The popularity of succinylcholine has been questioned, mainly in reference to its association with masseter spasm and malignant hyperthermia. Succinylcholine may also produce the severe side effect of hyperkalemia after burns, neurologic injury, and trauma, as well as increases in intraocular and intracranial pressure. The great advantage of succinylcholine is that it produces excellent intubating conditions, usually within a minute or slightly longer if pretreatment with a small amount (about one tenth of the intubating dose) of nondepolarizing relaxant is employed to diminish fasciculations and postoperative throat and skeletal muscle soreness. However, others believe that with this pretreatment the quality of intubating conditions is worsened. In sensitive individuals, frightening paralysis and even aspiration may occur. The rapid onset of adequate paralysis for intubation can be duplicated with rocuronium.^[23] However, succinylcholine maintains the advantage of rapid offset of action by ester hydrolysis. If the airway cannot be secured, the patient's own ventilation and airway maintenance will return much more quickly than with any of the currently available nondepolarizing relaxants. Succinylcholine is still the only relaxant with a duration of action (assuming normal pseudocholinesterase activity) that may provide for the resumption of spontaneous ventilation within a time sufficiently short that cerebral integrity can be maintained in the properly preoxygenated patient. When a muscle relaxant is to be employed in a difficult or potentially difficult airway, succinylcholine appears to be the relaxant of choice unless there are contradictions to its use, such as a risk of hyperkalemia.

The use of nondepolarizing relaxants for intubation has increased with the availability of short-acting compounds such as rocuronium. Atracurium, vecuronium, and cisatracurium are alternatives that are not quite as rapid in onset as is rocuronium.^[23]

Nasal versus Oral Route

In the operating room, nasal intubation is performed when surgery in the oral cavity or on the mandible is facilitated by an unobstructed view. If the mouth is to be wired or banded shut after surgery, a nasal tube must be used. Contraindications to nasal intubation include coagulopathy, severe intranasal disorder, basilar skull fracture, and a cerebrospinal fluid leak. If an oral tube is surgically unacceptable, and nasal intubation is contraindicated, the anesthesiologist must discuss the relative risks of tracheostomy and oral or nasal intubation in that patient with the surgeon to arrive at an acceptable compromise.

Nasal intubation is also used in the operating room in difficult airway situations. These include blind or fiberoptic intubation in the topicalized, sedated patient. Nasal intubation may be chosen because direct laryngoscopy is impossible; it may be quicker and more comfortable than oral intubation in the topicalized, sedated patient. Details on nasal intubations follow in the appropriate sections. Unlike oral intubation, nasal intubation may produce a bacteremia, and appropriate endocarditis prophylaxis should therefore precede it.^[24]

Oral Endotracheal Intubation

Oral endotracheal intubation is the usual method of intubation in the operating room. In adults, a rapidly acting anesthetic is usually given intravenously, mask ventilation is ensured, and a muscle relaxant is administered to facilitate laryngoscopy. In children, mask, rectal, and intramuscular inductions are frequently employed. Intubation may be performed with anesthesia and no relaxant, but a deep level of anesthesia must be achieved to avoid unforgiving reflexes such as laryngospasm. Unless there is a contraindication, the head is maintained in the classic sniffing position to align the oral, pharyngeal, and laryngeal axes (see Fig. 42-3 ). In adults, a small foam pillow or several folded sheets are often employed to maintain flexion in the lower cervical spine. The Popitz sniffing position pillow is an excellent way to establish a satisfactory position for mask ventilation and endotracheal intubation in the adult patient ( Fig. 42-17 ). It is important to use a head support that, unlike a big, soft pillow, does not allow the head to sink down into it. The laryngoscope is

Figure 42-17 A volunteer positioned on the Popitz pillow (DermaCare, Louisville, KY) demonstrates cervical flexion and a small degree of atlanto-occipital extension. The flexion aligns the laryngeal and pharyngeal axes. Further extension of the head results in the true sniffing position.

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After visualization of the epiglottis, the curved blade (e.g., MacIntosh) is inserted into the vallecula (i.e., space between the tongue and epiglottis), and the laryngoscope is pulled forward and upward ( Fig. 42-18 ) to expose the glottis. It is important to recognize structures sequentially as the blade is inserted and not just to insert deeply, pull, and hope for the best. The endotracheal tube is inserted into the right side of the mouth and inserted between the open vocal cords under direct vision ( Fig. 42-19 ). An assistant may help by pulling the right side of the mouth open to improve vision (especially with the Miller blade). Difficulties in visualization may be caused by head position, a blade that is too far advanced or not far enough advanced, or a reluctance on the part of the novice laryngoscopist to apply adequate but gentle upward force.

A straight blade is used in somewhat similar fashion except that it is usually advanced beyond the epiglottis, ensuring that the epiglottis is included in the structures

Figure 42-18 Proper position of the laryngoscope blade during direct laryngoscopy for exposure of the glottic opening. A, The distal end of the curved blade is advanced into the space between the base of the tongue and pharyngeal surface of the epiglottis (i.e., vallecula). B, The distal end of the straight blade (Jackson-Wisconsin or Miller) is advanced beneath the laryngeal surface of the epiglottis. Regardless of blade design, forward and upward movement exerted along the axis of the laryngoscope blade (arrows) elevates the epiglottis and exposes the glottic opening.

Figure 42-19 Schematic view of the glottic opening during direct laryngoscopy when the epiglottis is elevated with a curved or straight laryngoscope blade. The glottic opening is recognized by its triangular shape and the pale, white vocal cords. (From Stoelting RK, Miller RD: Basics of Anesthesia, 3rd ed. New York, Churchill Livingstone, 1994.)

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In men, the tube is generally inserted to about 23 cm at the lips to position the tube, with the tip an appropriate 4 cm above the carina. For women, the distance is about 21 cm. Tubes inserted too far cause endobronchial (usually right) intubation, whereas tubes that are not in far enough may be difficult to seal because of cuff protrusion through the larynx and carry a higher risk of accidental extubation ( Fig. 42-20 ). Exact placement of the tube requires a fiberoptic bronchoscope, but this is not usually necessary. Endobronchial intubation is easier to remedy than accidental extubation. In children, the distance (in centimeters) at the lips can be estimated from this formula: 12 + (age/2). In an age of laparoscopic surgery, clinicians must be aware that abdominal insufflation can shift the carina cephalad and convert an acceptable location to an endobronchial one.^[26]

A rapid-sequence induction is employed when the patient is at particular risk for aspiration and there is reasonable certainty that intubation should not be difficult ( Table 42-6 ). If there is sufficient doubt about the ability to intubate the patient in this setting, an intubation in the conscious patient with judicious use of topical anesthesia with or without sedation should be strongly considered. Before a rapid-sequence induction, the patient

Figure 42-20 Diagrammatic representation of key distances relating to endotracheal tube position. (From Stone DJ, Bogdonoff DL: Airway considerations in the management of patients requiring long-term endotracheal intubation. Anesth Analg 74:276, 1992.)

It is my practice to locate the cricoid cartilage in the conscious patient but not apply pressure until the patient is unconscious. This is because the proper amount of cricoid pressure is very uncomfortable in the awake patient, may provoke vomiting and obstruct the airway, is less likely to be effective in the patient before paralysis inhibits active vomiting, and has been shown to lower esophageal sphincter tone.^[27] The downward force on the cricoid cartilage required to occlude the esophagus appears to be approximately 30 to 40 N, about the force of an 8- to 9-lb weight.^[28] This may prevent regurgitation if applied properly, and because the force of vomiting is blunted by the muscle relaxant, the force should greatly decrease the risk of aspiration. There have been no studies proving that cricoid pressure is truly beneficial. ^[28] Incorrectly applied pressure cannot protect the patient from aspiration, because only the cricoid forms a complete ring that can occlude the esophagus. When intubation is difficult, cephalad (in conjunction with dorsal) cricoid pressure may aid visualization. Laryngoscopy and intubation in this setting are generally performed without any preceding manual ventilation, if possible. If intubation is not possible, mask ventilation should be provided while cricoid pressure continues. It is critical that the cricoid pressure be applied correctly so that it does not impede visualization of the glottis or passage of the tube. If glottic visualization or endotracheal tube passage is impaired, pressure may need to be diminished or entirely released to see if it is contributing to the problem. In addition to preventing regurgitation, cricoid pressure decreases the flow of gas to the stomach, minimizing gastric distention that can impede ventilation and predisposing to regurgitation. Pretreatment with an anticholinergic is recommended to minimize secretions that may impair visualization during a rapid-sequence intubation.

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Special Considerations

Laryngoscopy and intubation are powerful noxious stimuli, and the response may have deleterious respiratory, neurologic, or cardiovascular effects. Deeper levels of anesthesia are required to blunt the response to laryngoscopy and intubation than the response to surgical incision. When planning the anesthetic induction, these effects must be blunted to whatever degree is possible, especially if the patient is in a high-risk population (e.g., with coronary artery disease, asthma, elevated intracranial pressure, cerebral aneurysm).

NASAL ENDOTRACHEAL INTUBATION.

When nasal intubation is chosen solely for purposes of surgical convenience, anesthesia may be induced before intubation. A vasoconstrictor should be applied before nasal instrumentation. Cocaine (4% solution, up to 1.5 mg/kg) can be used, but phenylephrine (0.25% to 1.0% nose drops) is more readily available and less toxic. After anesthesia is induced and mask ventilation is established, the endotracheal tube is introduced into the nose in a plane that is roughly perpendicular to the face. The patient may be allowed to breathe spontaneously to facilitate blind intubation. In this case, the tube is inserted until maximum breath sounds are heard (usually about 14 to 16 cm in adults), indicating that the tube tip is just above the glottis. The tube is then inserted into the glottis during inspiration. Some clinicians choose to administer carbon dioxide to induce hyperpnea and facilitate intubation during spontaneous ventilation, but this is not common. Because entry into the glottis is not seen directly, it is essential to have capnographic or bronchoscopic confirmation of endotracheal placement because sometimes all the indirect signs of intubation may be misleading. Anesthetized blind nasal intubation may also be attempted in the apneic, paralyzed patient, but in this case there are no spontaneous breath sounds to aid placement, which is guided by external observation for tip location in the neck.

If the tube does not enter the glottis, the patient's head may be extended, flexed, or turned to guide the tip (if not contraindicated by spinal bony disease). If the tube tip is felt anteriorly, flexion may help; if the tip is felt beside the larynx (in the piriform sinus), turning the tube tip away from that side may help. Most of the time, the tube enters the esophagus, and extension of the head helps. If the trachea cannot be blindly intubated, the patient can be intubated with guidance under direct vision (after appropriate mask ventilation). In this situation, a curved laryngoscope blade appears to provide the greatest amount of space for maneuvering. The tube is inserted into the nose, and direct laryngoscopy is performed in the usual fashion. Under direct vision, the laryngoscopist may be able to direct the tip into the glottis. If not, Magill forceps may be used to carefully grasp the tube while avoiding trauma to the cuff. The tube can then be directed into the glottis, often with the help of an assistant who can push on the nasal end of the tube. If the glottis cannot be visualized by direct laryngoscopy, the Magill forceps can still be used to attempt to guide the tip blindly into the area of the glottis. Excessive force on the tube should be avoided because delicate laryngeal structures can be damaged or false passages created.

An anterior curve in the endotracheal tube may help in blind nasotracheal intubation. This can be accomplished by putting a stylet in the tube (removed before use) with the desired C-shape or by placing the tube tip in the 15-mm connector to form a circle. The time that the tube holds the curve can be lengthened by placing the curved tube in a refrigerator or freezer for some time before the case. An Endotrol endotracheal tube, which has an operator-end loop that directs the tube tip anteriorly when pulled, may be used. Another technique that uses cuff inflation has been described to further aid blind intubation.^[29] Because breath sounds must be audible, breathing must be spontaneous. When breath sounds are of maximal intensity, the endotracheal tube cuff is inflated with 15 mL of air, which tends to direct the tip anteriorly. The air is released from the cuff as the tube is passed (2 cm) through the glottis to avoid damage to the cords.

WHEN INTUBATION FAILS.

Every practitioner, no matter how skilled, encounters patients who are unexpectedly difficult to intubate. The induction of anesthesia should be approached with this possibility in mind so that a clear plan of action can be pursued. The prevalence of difficult laryngoscopy appears to be approximately 1% to 4% and is probably higher in the obstetric population. The degree of glottic exposure as described by Cormack and Lehane allows interobserver comparison of the difficulty of laryngoscopy ( Fig. 42-21 ). Patients of grade 4 difficulty and many patients of grade 3 view are likely to present difficulties and may even be impossible to intubate. In addition to difficult visualization, other pathologies, including epiglottitis, laryngeal or tracheal stenosis, and luminal tumors, may make translaryngeal passage of the endotracheal tube difficult.

When an initial attempt at intubation fails, mask ventilation should be resumed while the situation is reassessed. As long as mask ventilation can be maintained, the problem is not emergent. Cricoid pressure should be maintained when a full stomach is suspected. Head position and laryngoscopy technique need to be reexamined. The laryngoscopist may wish to exchange a curved for a straight blade (or vice versa). A longer MacIntosh blade (no. 4) can be useful in this situation. The Miller no. 4 blade is wider but not much longer than the no. 3 model. This width may help keep the tongue out of the visual field and provide a more effective fulcrum for displacement of the tongue muscle. If repeated laryngoscopy by an experienced practitioner is unsuccessful, a decision-branch point is reached if short-acting drugs (e.g., thiopental, inhalational anesthetic, succinylcholine) have been used. The patient may be allowed to awaken for an attempt at intubation with topical anesthesia, or the case may even be postponed if nonemergent. If long-acting drugs have been used (e.g., high-dose narcotic, nondepolarizing relaxant), mask ventilation must be maintained until reversal is possible. A task force of the American Society of Anesthesiologists (ASA) has developed an algorithm for the difficult airway, which is a useful guide in this setting ( Fig. 42-22 ). Benumof^[30] incorporated previously approved ideas and concepts into one flow

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Figure 42-21 Grades of difficulty in laryngoscopy: grade 1, no difficulty; grade 2, only posterior extremity of glottis visible; grade 3, only epiglottis seen; grade 4, no recognizable structures. (Adapted from Cormack RS, Lehane J: Difficult tracheal intubation in obstetrics. Anaesthesia 39:1105, 1984.)

If intubation cannot be accomplished, and the decision has been made to keep the patient anesthetized for intubation (or long-acting drugs have been used), a variety of other techniques can be used. First, help should be obtained, if possible. The assistant may provide laryngeal displacement such as a BURP maneuver, which is likely to improve glottic exposure. The assistant also provides a fresh pair of hands for mask ventilation and laryngoscopy and an objective viewpoint in what may be a rapidly deteriorating situation. An anticholinergic should be administered to reduce the secretions that often accumulate in this situation. If the arytenoids or epiglottis can be visualized, the gum elastic bougie represents an effective approach to intubation.^[31] This is the next approach to this situation at the author's institution. The elastic gum bougie is less effective in grade 4 views, but an attempt at entering the glottis can still be made. If a skilled bronchoscopist is available and mask ventilation is possible, fiberoptic bronchoscopy is probably best attempted immediately, before the field is obscured with blood and edema. However, this is not an ideal setting for the novice bronchoscopist. Other options include blind nasotracheal intubation or blind orotracheal intubation employing direct laryngoscopy with a curved blade and an endotracheal tube directed anteriorly with a stylet. The use of a lighted stylet or retrograde intubation may be appropriate and are described later.

The use of the LMA as a conduit for blind, bougie-guided, or fiberoptic intubation can be considered. Selected cases can proceed with an LMA or Combitube as airways. An LMA can also be inserted to facilitate ventilation until the effects of relaxants and other agents wear off. Other clinicians have suggested the Bullard laryngoscope (Circon ACMI, Stamford, CT) or the Augustine introducer (Augustine Medical, Eden Prairie, MN).^{[32] [33]} If multiple attempts fail and the case is not of an emergent nature, it is best to simply ventilate the patient until drugs can be reversed, because edema and blood may produce serious airway obstruction, preventing even mask ventilation. A patient for elective surgery who experiences intermittent laryngospasm and serious dysrhythmias is also a poor candidate for continued attempts at intubation.

WHEN MASK VENTILATION AND INTUBATION ARE IMPOSSIBLE.

The patient who is truly impossible to mask ventilate (i.e., two-handed mask ventilation with oral and nasal airways, complete forward mandibular dislocation, and bag ventilation by an assistant) or intubate presents a brain- and life-threatening emergency. As in so many instances in medicine, the best treatment is prevention. The clinician must always carefully evaluate the airway to determine the safest plan for intubation and extubation. In the patient who has been thoroughly denitrogenated, there should be sufficient time to institute one of the following interventions before serious oxygen desaturation and consequent hemodynamic deterioration occur. In reality, the clinician often is dealing with a severely hypoxic patient who has suffered or is near to cardiac arrest. It is critical to institute one of the following interventions before irreversible cardiac arrest or brain damage has occurred. If only short-acting drugs have been used (e.g., succinylcholine, thiopental, lidocaine) and the patient has been adequately preoxygenated, adequate spontaneous ventilation may resume before further intervention is required.

The LMA has become the next intervention in this situation; the Combitube is a reasonable alternative, particularly if aspiration is a major concern ( Fig. 42-24 ). If one of these supraglottic devices does not produce adequate gas exchange quickly, transtracheal jet ventilation (TTJV) should be instituted. In TTJV, a 14- or 16-gauge cannula is inserted through the cricothyroid membrane and attached to a high-pressure oxygen source by a low-compliance circuit ( Fig. 42-25 ). The review of Benumof and Scheller^[34] demonstrates that TTJV can provide

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Figure 42-22 Difficult airway algorithm developed by the ASA Task Force on Guidelines for Difficult Airway Management. (Adapted from American Society of Anesthesiologists Task Force on Management of the Difficult Airway: Practice guidelines for the management of the difficult airway. Anesthesiology 78:597, 1993.)

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Figure 42-23 Single-flow diagram version of the American Society of Anesthesiologists (ASA) Difficult Airway Algorithm. +, Always consider calling for help (e.g., technical, medical, surgical) when difficulty with mask ventilation or tracheal intubation is encountered; ++, consider the need to preserve spontaneous ventilation; *, nonsurgical tracheal intubation choices consist of laryngoscopy with a rigid laryngoscope blade (many types), blind orotracheal or nasotracheal intubation, fiberoptic or stylet technique, retrograde technique, illuminating stylet, rigid bronchoscope, and percutaneous dilational tracheal entry. Benumof^[30] offers a complete discussion of these tracheal intubation choices. (Adapted from Benumof JL: Laryngeal mask airway and the ASA difficult airway algorithm. Anesthesiology 84:686, 1996.)

A much less effective but more readily available system includes use of the standard anesthesia circuit or a self-inflating reservoir bag attached to the translaryngeal cannula (by a 3-mm ID endotracheal tube adapter placed directly into the cannula or an 8-mm ID endotracheal tube adapter placed into the wide end of a 3-mL, plunger-less syringe and then connected to the cannula).^[34] Successful TTJV should be followed with provision of a definitive airway by tracheostomy, endotracheal intubation, or wake-up and resumption of the normal airway. The most serious complications of TTJV involve some form of hyperinflation due to inadequate venting of inspired gases in the presence of complete or near-complete upper airway obstruction. This may result in barotrauma or diminished cardiac output in the context of an immediately life-threatening problem.

Although a classic tracheostomy usually cannot be performed quickly enough in the "cannot ventilate or intubate" situation, cricothyroidotomy can be employed to insert a small endotracheal or tracheostomy tube. A surgical blade (e.g., no. 11) on a handle and a Kelly clamp for spreading the incision are required. Kits with all the required materials are commercially available (Melker emergency cricothyrotomy catheter set, Cook Critical Care, Bloomington, IN). Although an experienced surgeon is the best choice to perform a cricothyroidotomy, the anesthesiologist must be prepared to do so if TTJV is

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Figure 42-24 Role of the laryngeal mask airway (LMA) in the American Society of Anesthesiologists (ASA) Difficult Airway Algorithm. (Adapted from Benumof JL: Laryngeal mask airway and the ASA difficult airway algorithm. Anesthesiology 84:686, 1996.)

DIFFICULT-AIRWAY CART.

The ASA Task Force on Difficult Airway Management has made the reasonable suggestion that a portable storage unit for a variety of intubation aids be readily available. Suggested equipment for this is listed in Table 42-7 . The bronchoscope cart itself is

Figure 42-25 Anatomy of the cricothyroid membrane. (Courtesy of Cook Critical Care, Bloomington, IN.)

Conscious (Awake) Intubation

Although emergency nonanesthetized intubations outside the operating room may be performed with minimal topical anesthesia and no sedation, the term awake intubation applied to nonanesthetized intubations in the operating room is usually something of a misnomer. After appropriate sedation, topical anesthesia, and nerve blocks, such intubations can be performed with minimal

Figure 42-26 Transtracheal jet ventilation apparatus assembled from components generally available in the operating room: 5.0-mm-internal diameter endotracheal tube adapter, oxygen tubing, and three-way stopcock. The connections can be banded for further security.

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Drugs for Intubation

SEDATION.

Narcotic analgesics are the key to facilitating conscious intubation. They afford mild sedation, analgesia, and reduction of airway reactivity that may result in cough and bronchospasm. Any narcotic may be used, but the overall characteristics of fentanyl have made it the most useful in such procedures. A lag in onset (i.e., hysteresis) of about 5 minutes for the full effect of fentanyl should be kept in mind as incremental doses of the drug are administered. Dose requirements also vary greatly between individuals (25 to 500 µg), and the drug should be administered slowly in small increments. The effect (or lack thereof) may not be apparent until the laryngoscope is inserted. Perhaps the greatest advantage of narcotics, especially fentanyl, is the ease of reversibility by naloxone if an undesired degree of respiratory depression results. Such patients may need to be reminded to breathe to ventilate adequately. If awake intubation is being performed because of a severe risk of aspiration, narcotics (and other intravenous sedatives) must be used sparingly.

To afford more sedation than a moderate dose of narcotics provides, a second drug is usually given. Droperidol (Inapsine) is a butyrophenone that supplies adequate sedation without adding to narcotic-induced respiratory depression. The drug is contraindicated in patients with Parkinson's disease because it blocks dopamine receptors and may produce a dystonic reaction. Doses of 1.25 to 5.0 mg given intravenously are usually adequate, although doses up to 10 mg have been used. The higher doses may be associated with bizarre side effects such as akathisia, dysphoria, and a prolonged state of sedation (up to 24 hours). To maximize the patient's comfort, it is best to administer a small dose of fentanyl before droperidol is given.

Other clinicians prefer to add a benzodiazepine to the narcotic effect. Midazolam (Versed), diazepam (Valium), or lorazepam (Ativan) may all be used, but midazolam is probably the most popular because of its relatively rapid onset and offset of action and the production of anterograde amnesia. The benzodiazepines should be administered slowly in small doses because their effect on consciousness, respiration, and cardiovascular status in individuals is unpredictable. Even 0.5 mg may produce adequate amnesia in some adults. Unlike droperidol, benzodiazepines result in increased respiratory depression in the presence of narcotics, which is usually manifest by apneic spells.^[38] Flumazenil, a specific reversal agent, is available clinically. The principal disadvantage of using benzodiazepines may be the profound decreased level of consciousness that results in loss of verbal contact with the patient, who in such situations must be able to respond to commands, especially to breathe. In the frail elderly patient, intravenous diphenhydramine (Benadryl) in doses of 12.5 mg may provide good supplemental sedation to narcotics without excessive respiratory depression or adverse mental effects.

ANTICHOLINERGICS AND TOPICAL ANESTHESIA.

Before any anticipated difficult intubation, a dose of anticholinergic such as glycopyrrolate (Robinul, 0.2 mg, given intravenously) is strongly advised. If bronchospasm is anticipated, larger doses (0.4 to 1.0 mg, given intravenously) are recommended to blunt the response to airway instrumentation. Besides improving visualization during laryngoscopy by reducing secretions, topical solutions of local anesthetics are less diluted and less likely to be washed off the desired site of application. The use of anticholinergics is reasonable for general anesthesia in any smoker, for surgical positions in which suctioning is difficult, for surgical positions in which secretions could loosen securing tape and predispose to tube dislodgment, and for surgery that involves the airway.

Anesthesia of the nares and nasopharynx should be accompanied by vasoconstriction to widen the available passage and decrease bleeding. Cocaine (4%) may be used

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The tongue and oropharynx can be anesthetized with 10% lidocaine spray, which is placed progressively further into the pharynx using the laryngoscope blade or a tongue depressor to keep the tongue out of the way. The cooperative patient can also gargle and expectorate viscous lidocaine to produce topical anesthesia of the tongue and pharynx. After there is sufficient anesthesia to allow the insertion of an oral airway, the long applicator adaptor for 10% lidocaine spray can be blindly placed through the airway to spray local anesthetic directly onto the supraglottic and glottic structures. Nebulization of 5 mL of 4% lidocaine can also be employed.

The larynx can be sprayed with additional lidocaine directly onto the visualized glottis. If a laryngotracheal applicator (LTA) kit is to be used, it can be inserted with some holes below the vocal cords and some above. This position can anesthetize the supraglottic area (including epiglottis) and the trachea when the lidocaine is injected. The trachea can also be anesthetized with a transtracheal (or more correctly, translaryngeal) application of 2 to 3 mL of 2% lidocaine. A 23-gauge needle is inserted perpendicularly through the cricothyroid membrane in the midline, air is aspirated to ascertain the location of the needle tip, the lidocaine is quickly injected, and the needle is removed (see Fig. 42-25 ). This may cause vigorous coughing in some patients, but coughing provides excellent spread of the anesthetic in the larynx below the vocal cords. Other practitioners insert a 14- or 16-gauge intravenous catheter through the cricoid membrane and remove the metal inner cannula before injecting local anesthesia. The catheter can be left in place to provide TTJV or access for retrograde intubation. The topical anesthesia produced in the larynx and trachea is suitable for the use of the elastic gum bougie or a direct attempt at intubation. Contraindications to such injections include coagulopathy and local disorders such as tumor masses.

The use of topical anesthesia of the airway in the presence of a full stomach should be approached with common sense. The nose, tongue, and oropharynx can be safely anesthetized, but similar anesthesia in the larynx and trachea may diminish airway protection to unacceptable levels.

NERVE BLOCKS.

The glossopharyngeal nerve provides the sensory input from the areas of the posterior tongue innervated by that cranial nerve. Glossopharyngeal nerve block is intended to provide more comfortable laryngoscopy with low doses of injected drugs. However, a study reported that viscous lidocaine swish and gargle followed by spray application of 10% lidocaine is as effective as glossopharyngeal block without producing the prolonged local discomfort seen in some individuals after the block.^[38]

The superior laryngeal nerve innervates the epiglottis, aryepiglottic folds, and the laryngeal structures down to the false cords. The superior laryngeal nerve (SLN) may be blocked by an external approach using a 23-gauge needle and 3-mL syringe to inject 2 to 3 mL of 1% lidocaine between the greater cornu of the hyoid bone and the thyroid cartilage. This block is contraindicated by coagulopathy, a local pathologic problem, or full stomach. The SLN may also be blocked by the application (for about a minute per side) of lidocaine-soaked gauze pads with Krause angle forceps held in the piriform fossa ( Fig. 42-27 ). This technique is frequently performed by otolaryngologists before laryngoscopy. The block may also be accomplished by several milliliters of lidocaine sprayed by the flexible laryngotracheal mucosal atomization device (MADgic, Wolfe Tory Medical, Inc., Salt Lake City, UT).

Choice of Technique

The choice of technique for conscious intubation depends on preference for oral or nasal tube placement, experience, and availability of equipment. If one technique fails, another is usually tried. All anesthesiologists should develop skill with conscious oral intubation with direct laryngoscopy. Blind nasal intubation that avoids the discomfort of laryngoscopy is equally important to learn. If fiberoptic bronchoscopy is an option, it should be performed reasonably early in the sequence because blood, secretions, and edema can make its use extremely difficult.

CONSCIOUS ORAL INTUBATION WITH DIRECT LARYNGOSCOPY.

Preparation for conscious oral intubation involves use of the drying agents, sedation, topical anesthesia, and nerve blocks previously discussed. Topical application of anesthesia to oropharynx and tongue without glossopharyngeal nerve blocks may allow for laryngoscopic visualization and further anesthesia of the glottis and the trachea with an LTA kit or similar device. The laryngoscope must be inserted gently but with firm manipulation when required. The requirement for sedation, topicalization, and nerve blocks varies greatly among patients so that care must be taken to avoid excessive doses while providing acceptable comfort levels. The use of the elastic gum bougie may improve comfort by reducing the force required to produce acceptable glottic exposure. Superior laryngeal blocks and transtracheal anesthesia are not generally used if there is a concern for aspiration of gastric contents.

To supplement the commonly used laryngoscope blades, a variety of ingenious blades have been devised to cope with the difficult intubation. In addition to a variety of shapes, mirrors (e.g., Siker blade) and prisms

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Figure 42-27 A, Superior laryngeal nerve block can be accomplished without injection by applying 4% lidocaine into each piriform fossa with a sponge or pledget mounted on Krause angle forceps. B, Similar application can be accomplished with the flexible laryngotracheal mucosal atomization device (MADgic, Wolfe Tory Medical, Inc., Salt Lake City, UT) by placing 3 to 4 mL of 4% lidocaine in each piriform fossa.

CONSCIOUS ORAL INTUBATION WITH INDIRECT LARYNGOSCOPY.

Unlike the flexible scopes, a rigid stylet fiberoptic laryngoscope is available for oral intubation only. The device is used to locate the glottis, but the stylet tip does not enter the larynx. The Bullard laryngoscope, an instrument for indirect laryngoscopy, is inserted much like a routine laryngoscope. The handle is then rotated from horizontal to vertical as the blade slides around the tongue. The endotracheal tube may be passed from the intubating attachment of the laryngoscope, or a tube containing a stylet in the shape of the laryngoscope may be used.^[33]

BLIND ORAL INTUBATION.

When there is minimal visualization of laryngeal structures during direct laryngoscopy, a blind or semiblind technique for intubation may be attempted in the conscious or anesthetized patient. A MacIntosh blade is helpful to pull up the tongue and thereby open up and maintain the airway. An endotracheal tube with a curved stylet is then guided in the presumed direction of the glottis, where the tube is then slid off, ideally into the trachea. Spontaneous ventilation is helpful because breath sounds can guide the way to the larynx. After a blind intubation, confirmation of endotracheal intubation with capnometry or bronchoscopy, or both, is advisable. To change the direction of the tube tip, stylets with a tip-moving device have been designed (Flexguide, Scientific Sales International, Kalamazoo, MI). The Magill forceps may also be used to guide the tube tip in the desired direction. Even the clinician's fingers may be used in a blind, tactile technique. The first and second fingers of the nondominant hand are placed on either side of the tip of the epiglottis to guide the tube. The patient must be cooperative, or the anesthetist risks getting bitten. The Augustine guide includes a curved positioning blade with a guide channel that fits in the vallecula. The tip is then moved anteriorly to expose the vocal cords, and an endotracheal tube is slid over a flexible stylet that has been passed into the trachea after confirmation of easy air aspiration.^[32]

Stylets with lights at the tip (i.e., lightwand stylet) are advantageous in that the stylet tip can be guided by observation of the light's movement under the skin (Flexilum, Concept Corp., Clearwater FL; Tubestat, Xomed-Treace, Jacksonville, FL). These are useful when mouth opening or neck movement is limited. The room must usually be quite dark to see the light adequately. When the tube tip is correctly positioned just above the vocal cords in the midline, a distinct glow is seen in the anterior neck, and the tube is slid off into the trachea.

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NASAL INTUBATION IN A CONSCIOUS PATIENT.

Conscious nasal intubation is useful for urgent intubations outside the operating room when mouth opening or neck movement is limited or prohibited and when a nasal endotracheal tube is required but anesthesia and paralysis are thought to be too risky. Topical anesthesia of the nose and oropharynx as described is as important as an appropriate amount of sedation. The supraglottic area can be anesthetized with superior laryngeal blocks or local anesthetic sprayed through the tube during its passage. Translaryngeal anesthesia is especially useful for blind, conscious nasal intubation. The lubricated, curved endotracheal tube is inserted perpendicularly into the nose and gently passed into the hypopharynx. If breath sounds disappear, the tube has passed into the esophagus or a piriform sinus and must be withdrawn above the level of the glottis. A variety of devices have been employed to amplify the breath sounds, but the ear over the end of the tube is usually adequate. Occasionally, vomiting or bronchial secretions make this an unpleasant experience. Capnography may be used to assist in the process of placement in addition to confirmation of proper position. The tube is passed into the larynx during inspiration, which tends to be deepest immediately after a cough. Some clinicians ask the patient to pant to maintain an open glottis with plenty of air movement. "Nasal Endotracheal Intubation" describes several techniques for facilitating passage of the recalcitrant endotracheal tube. If the mouth can be opened, direct laryngoscopy and Magill forceps can be used to guide the tube into the glottis. If direct laryngoscopy is necessary, further airway anesthesia, heavier sedation, or glossopharyngeal blocks probably will be required.

RETROGRADE ENDOTRACHEAL INTUBATION.

Retrograde intubation involves passage of a wire or plastic stylet through the cricothyroid membrane that is then coughed out of the larynx and into the oropharynx by the patient. This may be done in the anesthetized or conscious patient. In the conscious patient, it should be preceded by transtracheal topicalization. In adults, this can be done with a long-arm central venous pressure catheter or epidural catheter passed through the accompanying needle. In children, a 20-gauge intravenous catheter with a 0.021-inch J wire is appropriate. A J-wire technique can also be used in adults. A kit with a J wire (Cook Critical Care) can be used to insert endotracheal tubes as small as 4-mm ID ( Fig. 42-28 ). If a nasal tube is desired and the wire or catheter comes out of the mouth, the tip can be secured to a nasally passed catheter and then pulled up and out through the nose. The endotracheal tube is then inserted into the larynx over the wire, which is held with mild tension. The tip of the tube may catch on the anterior commissure and therefore not pass. Turning the tube, loosening the wire, or threading the tube onto the wire by means of the Murphy eye (rather than the bevel tip)

Figure 42-28 Retrograde intubation with the Cook Retrograde Intubation Set. A, After placement of an 18-gauge sheath needle into the larynx, the J end of the guidewire is inserted in a cephalad direction until it exits the mouth or nose. B, An 11.0-French Teflon catheter is threaded down over the guidewire until it contacts the laryngeal access site. The guidewire is removed from above. C, After advancing the Teflon catheter 2 to 3 cm, the endotracheal tube is advanced into the trachea while maintaining constant control of the catheter. (Courtesy of Cook Critical Care, Bloomington, IN.)

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Fiberoptic Bronchoscopy

Fiberoptic bronchoscopy is a technique that may be used for all of the difficult airway situations previously described in this chapter. The scope may be used to evaluate possible obstruction of the endotracheal tube, rule out esophageal intubation, check for endobronchial intubation, and ensure the correct placement of double-lumen endobronchial tubes. Much like that of the traditional laryngoscope, skillful use requires practice in situations that are neither urgent nor extremely difficult. This may initially include practice on a teaching mannequin. Even in experienced hands, successful intubation with the fiberoptic scope usually requires several minutes, and another technique therefore should be used if an airway must be established rapidly in the face of severe hypoxia. When use of the bronchoscope is anticipated for the more elective management of a difficult airway, the bronchoscope should be employed first before airway visualization is obscured with blood, secretions, and edema. Pathologic processes such as tumors, infection, and edema that diminish the space between the anterior and posterior pharyngeal wall may make passage of the bronchoscope difficult.

The bronchoscope itself contains thin glass fibers that transmit reflected light along their length. The fiber size (5- to 25-μm diameter) is chosen for flexibility, strength, and light transmission. In addition to the image-transmitting bundle of fibers, there is another light fiber bundle that transmits the light from a powerful source. The instrument also includes wire controls for changing angulation of the tip and a port for suction or injection of local anesthetics and oxygen. The bronchoscope is a relatively delicate instrument and must always be handled with care. Because replacement or repairs are very expensive, the scope should be turned only as a unit and not twisted on its shaft. The monograph by Ovassapian^[42] supplies details concerning care and cleaning of the instrument and has many photographs and illustrations of great utility to the bronchoscopist.

If oral intubation is planned, an endoscopic oral airway or bite block is best used to protect the bronchoscope. The oral airway also has the advantages of preventing dorsal displacement of the tongue, keeping the instrument in the midline, and guiding the bronchoscope past the epiglottis into the larynx. Such devices include the Patil-Syracuse airway, the Williams airway intubator, and the Ovassapian intubating airway.^[42] If an anesthetized intubation is planned, a mask with a sealing endoscopy port can be used to maintain anesthesia with spontaneous or controlled ventilation during the bronchoscopy.

Before any fiberoptic procedure, a dose of an anticholinergic drug is strongly recommended to prevent secretions from obscuring the view in the upper airway. The light source should be checked and the bronchoscope prefocused on printed material. The tip of the bronchoscope should be defogged with commercial solution or warm soapy water. The bronchoscope is lightly lubricated along its entire length with a water-soluble agent (i.e., K-Y jelly or eye lubricant) to facilitate passage through the endotracheal tube. A patent suction port is important, and a syringe with 10 mL of 1% lidocaine solution can be attached for further topical spray through the bronchoscope. If oxygen insufflation is desired, an appropriate source adaptable to the bronchoscope port should be available, which is useful in keeping secretions off the tip and diminishing fogging, as well as providing a source of 100% oxygen. However, it also poses the potential for marked gastric insufflation before the trachea is entered and for barotrauma after tracheal entry.

The bronchoscopist must decide whether the intubation will be nasal or oral and conscious or anesthetized. Nasal intubation has the advantage that the fiberoptic scope is usually positioned to directly visualize the glottis and is therefore technically easier. During conscious, sedated nasal intubation, there is less interference by the tongue. An intubating airway is not required, but a standard airway may be used to keep the tongue off the posterior pharyngeal wall during anesthetized intubations. Some clinicians use a soft nasal airway that has been split lengthwise to introduce the bronchoscope. The previously discussed contraindications to nasal intubation apply. If there is doubt about the ability to maintain the mask airway, intubation should proceed with conscious sedation only. The patient can be anesthetized for fiberoptic intubation if the mask airway can be maintained but intubation is difficult. Such anesthetized intubations are usually more difficult because of the development of upper airway obstruction.

Sedation and topical anesthesia of the airway have been previously addressed in this chapter. In the conscious, sedated patient, superior laryngeal blocks and translaryngeal anesthesia may be applied. Alternatively, the supraglottic, glottic, and tracheal areas may be topicalized with 1% lidocaine sprayed through the injection port.

For conscious, sedated nasal insertion, the patient's nares and nasopharynx must be anesthetized and vasoconstricted as previously described. The endotracheal tube or split nasal airway is inserted into the posterior nasopharynx and the fiberoptic bronchoscope passed through it. In most cases, the glottis can then be seen with minimal tip manipulation. The appearance of the glottis is quite different during fiberoptic bronchoscopy from the stretched appearance the laryngoscopist expects during classic rigid laryngoscopy. The endotracheal tube can be inserted into the nose under bronchoscopic guidance if there is concern about a foreign body or if the tube can enter the nares but not pass into the oropharynx. A useful alternative method is to blindly insert the endotracheal tube until breath sounds are heard maximally, as in blind nasotracheal intubation. This usually results in an easily visualized glottis that is quite close to the bronchoscope tip. Occasionally, a deviated septum compresses the endotracheal tube and makes passage of the bronchoscope difficult.

Sedated, fiberoptic oral intubation is somewhat more difficult than nasal intubation because the epiglottis becomes a greater obstacle and the tube tip is not usually

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Fiberoptic intubation in the anesthetized patient may be performed with spontaneous or controlled ventilation with a standard or Patil endoscopic mask. Other clinicians use some form of insufflation to provide oxygen without a mask. Spontaneous ventilation has the obvious advantage of avoiding apnea while bronchoscopy takes place. However, a diminished anesthetic level may result in cough, vomiting, laryngospasm, and bronchospasm. The patient must be ventilated by mask with 100% oxygen between intubation attempts. During bronchoscopy, oxygen may be administered through the injection port, but insufflation requires an additional source of oxygen. The endoscope mask has a sealing port that allows for the continuous use of a sealed mask airway during bronchoscopy. If a specialized mask is unavailable, a substitute may be constructed by placing the endotracheal tube cuff into the mask inlet to form a seal and then placing a fiberoptic swivel connector on the endotracheal tube to allow simultaneous bronchoscopy and mask ventilation through the anesthesia circuit. For any fiberoptic, anesthetized intubation, an assistant is required to hold the endoscopic mask, maintain the airway, deliver equipment, and sometimes help stabilize the endotracheal tube while the bronchoscope is inserted.

If nasal, anesthetized intubation is planned, vasoconstriction of the nares and nasopharynx is necessary. The technique of bronchoscopy is as previously described but may be somewhat more difficult because of soft tissue upper airway obstruction caused by anesthesia or paralysis. Pulling the tongue anteriorly as previously described may aid visualization of the glottis. Anesthetized, oral intubation is probably the most difficult of the four possible techniques.

The bronchoscopist may choose to stand at the head or the side of the table. If the patient cannot lie flat, standing at the side is essential, but standing on the side of the bed makes the procedure less awkward. The sitting position may facilitate visualization by gravity drainage of secretions and by pulling the scope tip toward the larynx. Keys to successful intubation include control of secretions, bronchoscopic intervention before extensive bleeding and edema have occurred, adequate topical anesthesia and sedation, proper defogging of the lens, and aligning the scope in the midline. Occasionally, the bronchoscope enters the trachea easily, but the endotracheal tube cannot be advanced over it. This is usually caused by the bevel catching on the right arytenoid (oral) or epiglottis (nasal), depending on the approach.^[43] This problem may respond to turning the tube 90 degrees counterclockwise and then 180 degrees, if necessary. This difficulty can largely be eliminated by the use of special tubes like the Parker Flex-Tip tube (see Fig. 42-14 ). Careful laryngeal and neck manipulation may also help. If a small (4-mm) bronchoscope has been used, the substitution of a larger (6-mm) instrument may prove helpful. Alternatively, a smaller endotracheal tube may be necessary. The use of an anode or flexible reinforced tube has been reported to be advantageous.^[44] Sometimes, sliding the tube in as the bronchoscope is withdrawn works. Excessive force should be avoided to minimize laryngeal trauma and trauma to the delicate fibers at the tip of the scope.

Bronchoscopy is difficult in the presence of bleeding or airway edema. Severe edema or anatomic airway distortion occasionally necessitates another approach to airway management if surgery must be performed. The presence of a large epiglottis flopping against the posterior pharyngeal wall occasionally is an insurmountable problem. If the location of the bronchoscope tip is uncertain, the bronchoscope has usually entered a piriform fossa that may resemble the glottis in this situation. When direct visualization cannot be accomplished, the room lights can be dimmed and the strong light at the bronchoscope tip observed and manipulated into the midline, much like a lightwand stylet.

Removal of the bronchoscope may be difficult. It is essential that the tip manipulation lever be in the unlocked, neutral position. The bronchoscope should not be removed with undue force because the fibers may be damaged, the patient injured, or the endotracheal tube displaced. This is most likely to occur with a poorly lubricated bronchoscope used in a relatively small-bore tube. It may also be caused by pinching of the tube in a tight nasal passage or an errant tip that has gone out through the Murphy eye. In this situation, bronchoscope and tube may have to be removed as a unit and the procedure begun again.