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ASSOCIATE EDITORS: JOHN F. BUTTERWORTH IV, M.D.
The American Society of Anesthesiologists, Inc.
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The most taxing part of performing an awake intubation (AI) should be making the decision that it is needed! When the decision has been made, the means forsecuring the airway should be routine for you and comfortable for the patient. This isnot a refresher course on flexible fiberoptic-aided intubation. First, I review astrategy for determining whether an AI is indicated; then I describe my approach topatient preparation. Finally, when the patient is prepared, the ‘‘tool’’ to be used canvary (e.g., flexible fiberoptic intubation scope, supraglottic airway, direct laryngo-scope, or videolaryngoscope optical stylet). Importantly, the ‘‘awake’’ patient may besedated and amnestic but should be able to cooperate with procedures and protecthis or her own airway. In some cases, an unconscious and spontaneously breathingstate may be appropriate (e.g., the patient who may be a difficult case forlaryngoscopy but is not at risk for upper airway obstruction or gastric contentsaspiration), but these special circumstances will not be the subject of this discussion.
The clinician must apply his or her own experience and judgment when using the Airway Approach Algorithm (AAA)- -the AAA provides no absolute answers. Thepurpose of the AAA is to guide entrance into the American Society of Anesthesio-logist’s Difficult Airway Algorithm1 as will be made clear in the following discussion.2 Factors including the patient’s disease and informed consent, consultation with other physicians, and the anesthesiologist’s own medical assessment of the patientdetermine the answer to this question. It is this author’s opinion that the physicianwho will assume responsibility for airway management procedures has the mostimportant opinion. Nevertheless, it is the responsibility of that physician to explainthe rationale for his or her decision to the other parties involved. In some cases,airway manipulation can be avoided by regional anesthesia. When a decision is madeto proceed without airway manipulation, one should nevertheless conduct a fullevaluation of the patient’s airway should conversion to a general anesthetic berequired.
The ease of laryngoscopy and intubation must be evaluated in all patients about to undergo interventions that may affect the airway. Many authors have attempted todelineate the factors that describe the difficult patient airway. Table 1 lists the most Copyright Ó2009 American Society of Anesthesiologists, Inc.
Commonly Cited Physical Examination Indices of Laryngoscopy common techniques in use today. Also included in this table are the results ofsensitivity and specificity testing of these indices. It should be noted that thesestandard methods of evaluation have been shown to have low and variable sensitivityand marginal specificity when used to predict the ease of direct laryngoscopy, andtheir sensitivity and specificity for videolaryngoscope remain unknown.3--7 Evaluationof the airway for the purpose of identifying the difficult-to-intubate patient remainsvexing. There is a continuing search for new predictive physical examinationfindings. Overall, the relationship of each test to other anatomic findings is rarelyconsidered. The published indices tend to treat each physical finding in isolationfrom all others, when in fact they are really interdependent.8 Almost no data exist onthe prediction of ease of videolaryngoscopy. If the clinician is satisfied thatlaryngoscopy (direct or video) will be straightforward (the answer to question I is‘‘no’’), then he or she may proceed as seems clinically appropriate given the clinicalneeds and the risk of aspiration. This is equivalent to the root point of the AmericanSociety of Anesthesiologist’s Difficult Airway Algorithm box ‘‘B’’ (Fig. 1).1 If theanswer to question II is ‘‘yes,’’ then the AAA proceeds to question III.
The Airway Approach Algorithm
II) Could your † laryngoscopy be (at all) difficult? III) Could your † supralaryngeal ventilation be used (if needed)? IV) Is the stomach empty? (is there an aspiration risk?) V) Will the patient tolerate an apneic period? ASA Difficult Airway Algorithm root points
A. Awake intubation
B. Intubation attempts after
the induction of anesthesia
A decision tree approach to the preoperative assessment of the patient airway: the airway approach algorithm.2 † Specific to your chosen method of laryngoscopy, e.g., direct orvideo. ASA ¼ American Society of Anesthesiologist; TTJV ¼ transtracheal jet ventilation.
Clinical Factors Predictive of Difficulty With Mask Recent studies have provided some unexpected findings regarding patients who might present problems with bag and mask ventilation.9,10 Langeron et al.
investigated the delineated clinical factors that described these patients. The studyheightens our awareness that there are a defined number of patient situations inwhich one should suspect a problem (Table 2).
Might Supralaryngeal Devices Be Used (If Needed)? Supralaryngeal devices include the laryngeal mask airway (LMA) and the Combitube, and both devices can be used in either elective or rescue situations.11Curiously, only one actual study has investigated the LMA in ‘‘cannot intubate/cannotventilate’’ situations. Parmet et al.11 were able to rescue 16 of 17 ‘‘cannot intubate/cannot ventilate’’ patients using the LMA. The single patient who could not berescued was found to have intratracheal blood clots, believed secondary to attemptsat transtracheal jet ventilation. The Combitube has been shown to have a 97 to 99%success rate in prehospital airway rescue in patients who could not be intubated.12,13Factors that preclude the use of the Combitube and LMA include small mouthopenings, mass lesions in the oropharynx, and ‘‘full stomach’’ conditions (althoughthe Combitube and possibly the new Proseal-LMA offer some airway protectionagainst aspiration14,15). Certain esophageal conditions, including caustic ingestion,argue against use of the Combitube. New supraglottic airways (e.g., the LaryngealTube, Cobra; VBM Medizintechnik, Sulz, Germany) have also been successfully usedin the ‘‘cannot intubate/cannot ventilate’’ situation. However, what should one do ifone’s assessment leads him or her to suspect that supraglottic ventilation may bedifficult? We have already determined that this patient may be a difficult case forlaryngoscopy (the preoperative equivalent of ‘‘cannot intubate’’), and now we havedetermined that a possible ‘‘cannot ventilate’’ scenario might occur. As we neverwant to place our patient in danger, ‘‘box A’’ (AI) is chosen (Fig. 1).1 If it is judgedthat supraglottic ventilation will be possible, we proceed to the next AAA question.
Recognizing that the decision regarding supraglottic ventilation adequacy may bedifficult, question V will later address the problem of error.
Opinions vary widely as to what patient conditions define a risk for aspiration.
Research regarding gastric-emptying times and the development of new pharma-ceutical agents has changed the meaning of ‘‘aspiration risk.’’ If there is a perceivedaspiration risk, then we have reached a potential scenario of ‘‘cannot intubate’’ and‘‘should not ventilate.’’ When intubation has failed, the American Society ofAnesthesiologist’s Difficult Airway Algorithm branches to mask ventilation. As mask ventilation is relatively contraindicated in the current assessment, we have onceagain found ourselves in the emergency pathway and so will preoperatively choose‘‘box A’ (AI) (Fig. 1).1 If there is no aspiration risk, we can proceed to the finalquestion of the AAA.
Will the Patient Tolerate an Apneic Period? If our assessment of the patient with regard to the difficulty of intubation is correct, but our assessment of ventilation is erroneous, the patient will experience aperiod of apnea after the induction of anesthesia. The duration of apnea will bedependent on patient health issues and administered drugs. Similarly, the time forcritical oxygen desaturation will vary with patient health as well as the extent ofpreoxygenation (a discussion of each of these factors is beyond the scope of thecurrent lecture16). Should it be determined that the patient would not tolerate amisjudgment in question III, ‘‘box A’’ (AI) is chosen.1 If the patient should be able totolerate a duration of apnea, which will allow the resumption of spontaneousventilation, or provide the clinician enough time to institute alternative rescuemeans, routine induction is undertaken (‘‘box B’ ) (Fig. 1).1 The experiencedclinician may consider an advanced exception in the ‘‘failure in judgment’’ decisionbranch (question V, answer ‘‘no’’). As can be seen in Figure 1, a footnote on the ‘‘AI’’branch indicates that the clinician may ‘‘consider the feasibility of transtracheal jetventilation.’’ Transtracheal jet ventilation can rapidly correct hypoxemia wheninitiated promptly and administered correctly. Available equipment (appropriatecatheter and high pressure oxygen source), patient habitus (accessible cricothyroidmembrane), and the physician’s experience will dictate the practicality oftranstracheal jet ventilation in the event of oxyhemoglobin desaturation.
Airway evaluation should result in a plan that considers all aspects of the patient’s airway, not just whether direct laryngoscopy is likely to be easy. Every time we areasked to manage an airway, or to use pharmaceuticals or perform proceduresthat might compromise the patient’s ability to maintain a patent airway, wemust consider alternatives. The supraglottic airways provide new possibilities incontrolling ventilation. By asking the appropriate questions, all necessary informa-tion regarding management of the airway is elicited. The ‘‘cannot intubate’’ or the‘‘cannot intubate/cannot ventilate’’ condition may still arise, but the clinician will bebetter prepared, having already gathered the critical information.
AI is a critically important tool. If you manage airways, you must be good at AI (one day you will need it)! If you have not performed an AI in years, your indicationsare probably too restrictive. My experience suggests that the typical anesthesiologistis insecure about his or her AI technique and confuses airway anesthesia techniques with the AI technique. AI is not about producing a ‘‘numb’’ airway. The topicalanesthetic(s) chosen matters little. AI involves a systemic approach to patientpreparation. When one has developed a consistent technique, AI can become as easyas routine airway management (Table 3).
All patients presenting to the operating room for surgery harbor some degree of anxiety. Although we may be comfortable in the operating room, it is a foreignenvironment for most others, and surgery is most often a daunting prospect. Patientswant the safest experience possible. If you have determined that AI is warranted, youhave erred on the side of HYPERLINK "mailto:safety@" safety---and the patient willunderstand this. A clear explanation to the patient will usually suffice to gain thepatient’s cooperation. Explaining that they will feel or remember very little and thatthey will have some sedation is all that is needed.
To desiccate is to ‘‘dry.’’ Before you begin to manipulate the airway below the nasopharynx, it should be dry for a number of important reasons: (1) saliva is aprotective barrier---it will protect the mucosa from your topical local anestheticagents; (2) manipulation of the airway produces more secretions---these secre-tions are an airway stimulant, causing more cough, laryngospasm, etc., and (3)visualization through an indirect optical device can easily be prevented by excessivesecretions. My favorite desiccant is glycopyrolate (0.2 to 0.4 mg) given intravenously.
Atropine and scopolamine are also effective. Whichever agent you choose, it must begiven time to work---at least 15 minutes. I will often give the dessicant in the patientintake area as soon as the patient has changed clothes. If there is no intravenousdevice in place, I do not hesitate to use an intramuscular injection. This assures thatthe agent will have time to be effective. If, by the time the patient reaches theholding area, they are not complaining of ‘‘cotton mouth,’’ I consider giving another0.2 mg.
This is primarily a reminder to ‘‘prepare the nose,’’ which I do in all cases unless medically contraindicated, regardless of my intent to intubate via the mouth or nose. Avasoconstrictor is used to decongest the nasal mucosa. This widens the space andreduces the risk of bleeding during manipulation. Oxymetazoline (e.g., Afrin; Schering-Plough Corporation, Kenilworth, NJ; Gensol; Major Pharmaceuticals, Livonia, MI) iseffective and long acting. Why do I prepare the nose in all cases? (1) Local anestheticpreparation of the nose also anesthetizes parts of the oropharynx by both cross innervation and passive spread of local anesthetic. (2) When oral intubation provesdifficult, the nose is ‘ ready to go’ - -too many times I have seen the plan changed fromoral to nasal intubation. Preparation of the nose is often started in the intake area.
Except for cases of retrograde intubation with a cricothyroid puncture, I do not use nerve blocks for airway anesthesia. I have no objection to ‘‘needle’’ blocks; I havenot found them necessary. I use the same topical anesthetic technique in all caseswhether I intend to intubate by a nasal or oral route, regardless of which instrument Iplan to use. I divide the airway into three areas and use directed blocks for each:nasal passage/nasopharynx, base of tongue/posterior oropharyngeal wall, hypophar-ynx/larynx--trachea. If the patient coughs during the topical administration, he or sheis told that the ‘‘local anesthetic is getting to the right place.’’ I also do not usenebulized local anesthetic; nebulized local anesthetics completely abolish the coughreflex, which I generally try to avoid.
This area is innervated by the anterior ethmoid nerve (anterior one-third) and nasopalantine nerve. I take cotton swabs soaking with local anesthetic (4% lidocainesolution or 5% lidocaine ointment) and advance them slowly into the nasal passage,directly posterior until the boney feel of the sphenoid bone is encountered. Progressis incremental. I advance the swab until the patient winces or otherwise exhibitsdiscomfort. After a brief hiatus (30 seconds), I continue on. Full anesthesia of thenose may take as long as 5 minutes to accomplish.
Base of Tongue/Posterior Oropharyngeal Wall These are the only two areas in the mouth and pharynx that concern me. I do not concern myself with the oral cavity; my dentist regularly performs an aggressive oralexamination, which I readily accept unless he accidentally stimulates my gag reflex.
The glossopharyngeal nerve is responsible for the gag. We can access theglossopharyngeal nerve where it travels in the base of the palatoglossal arch---thatarch of tissue, which travels from the uvula to the base of the tongue. A new set oflidocaine-soaked swabs are inserted along the tongue until they contact the anteriorsurface of the base of the arch. Some patients will respond to this with a retch. Thisis a good indicator that you are in the correct position. A few moments later, theswab can generally be reapplied. The patient can close his or her mouth on theswabs and hold them in position for 5 minutes (Fig. 2).
Many years ago at an American Society of Anesthesiologist’s annual meeting I learned a ‘‘trick’’ from a young anesthesiologist: a 5-ml syringe fitted with a largeplastic angiocatheter is filled with lidocaine (2%). The patient extends the tonguemaximally, and the anesthesiologist takes an unfolded gauze, neatly wraps the tip ofthe tongue, and does not allow the patient to retract. After the patient is assured thatthere is no needle, the catheter is inserted over the tongue until the distal tip is at theoral--pharyngeal juncture. Slowly lidocaine is ‘‘dripped’’ onto the tongue base. Theprocedure may take up to 1 to 2 minutes, and all 5 ml of lidocaine need not be used.
At first, the patient will cough. When the coughing subsides, yet you can hear thegurgling of the lidocaine deep in the airway, you can let go of the tongue. Holding The glossopharyngeal nerve can be blocked with the application of lidocaine on the inferior aspect of the palatoglossal arch (arrow).
the tongue in this manner prevents the patient from swallowing the lidocaine andencourages its aspiration.
If a flexible fiberoptic scope is used for the tracheal intubation, local anesthetic can be injected down the ‘‘working channel.’ I prefer a technique I first hearddescribed by Dr. A. Ovassapian: an epidural catheter is placed via the working port.
Local anesthetic is then administered via the catheter (be sure to cut off amultiorifice end). This has several advantages: the image is not obscured by theliquid, the stream can be aimed to the area of need, and suction or oxygen can beadministered at the same time.
At most I use 400 mg lidocaine (100 mg ointment in the nose and mouth each, 100 mg 2% viscous lidocaine in the hypopharynx, and 100 mg 2% solution via thefiberscope). Studies have proven this to be an extremely safe level of localanesthetic, producing peak serum levels of 0.5 mg/ml 11 hours, after administration(toxic levels being 4 4 mg/ml).17 I am often asked by colleagues to advise on the care of patients who have undergone extensive upper airway surgery and/or radiation. In these patients, nerveblocks may be difficult or impossible (because of altered anatomy). These airwaysare, paradoxically, often the easiest in which to perform AIs! The patients are usuallyaware of the anesthetist’s challenge and are motivated to cooperate. There may bereduced saliva production resulting from previous radiation and surgical manipula-tion. There may be postsurgical reduction in sensation.
Any of a long list of sedative agents can be used: benzodiazepines, opiods, droperidol, haldol, benedryl, or dexmedetomidine. There are three rules I follow: (1)judicious titration- -do not give significant boluses of the drugs; (2) avoid poly-pharmacy- -stay with one or two agents; and (3) have reversal agents available. Finally,do not confuse deep sedation with AI. During AI, the patient should be able tocooperate with procedures and to control his or her own airway (including coughing).
AI is undertaken when the clinician has decided that it is necessary for the well- being of the patient. As such, the described procedures should be executed at acontrolled pace and in a composed environment. ‘‘Procrastination’’ is a tongue-in-cheek way of saying ‘‘do not rush into the operating room.’’ The operating room is ahighly pressured environment, and it is difficult venue in which to allow adequatetime for antisialogogues and topical anesthetics to produce their therapeutic effect.
We can best achieve our goals by starting our procedures early, if possible, in theholding area.
Hopefully, now when presented with a patient with a challenging airway, you will have a strategy for determining whether an AI is indicated and a safe and effectiveapproach to patient preparation.
1. American Society of Anesthesiologists Task Force on Management of the Difficult Airway: Practice guidelines for management of the difficult airway: An updated report by theAmerican Society of Anesthesiologists Task Force on Management of the difficultairway. Anesthesiology 2003; 98:1269--77.
2. Rosenblatt WH: The airway approach algorithm: A decision tree for organizing preoperative airway information. J Clin Anesth 2004; 16:312--6.
3. Cormack RS, Lehane J: Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39: 4. el-Ganzouri AR, McCarthy RJ, Tuman KJ, Tanck EN, Ivankovich AD: Preoperative airway assessment: Predictive value of a multivariate risk index. Anesth Analg 1996; 82:1197--204.
5. Oates JD, Macleod AD, Oates PD, et al.: Comparison of two methods for predicting difficult intubation. Br J Anaesth 1991; 66:305--9.
6. Yamamoto K, Tsubokawa T, Shibata K, et al.: Predicting difficult intubation with indirect laryngoscopy. Anesthesiology 1997; 86:316--21.
7. Savva D: Prediction of difficult tracheal intubation. Br J Anaesth 1994; 73:149--53.
8. Rosenblatt WH: Airway management, critical surgical illness: Preoperative assessment and planning (supplement). Crit Care Med 2004; 32:S186--92.
9. Kheterpal S, Han R, Tremper KK, et al.: Incidence and predictors of difficult and impossible mask ventilation. Anesthesiology 2006; 105:885--91.
10. Langeron O, Masso E, Huraux C, et al.: Prediction of difficult mask ventilation. Anesthesio- 11. Parmet JL, Colonna-Romano P, Horrow JC, et al.: The laryngeal mask airway reliably provides rescue ventilation in cases of unanticipated difficult tracheal intubation alongwith difficult mask ventilation. Anesth Analg 1998; 87:661--5.
12. Blostein PA, Koestner AJ, Hoak S: Failed rapid sequence intubation in trauma patients: Esophageal tracheal combitube is a useful adjunct. J Trauma 1998; 44:534--7.
13. Davis DP, Ochs M, Hoyt DB, Vilke GM, Dunford JV: The use of the combitube as a salvage rescue device for paramedic rapid sequence intubation. Acad Emerg Med 2001; 8:500(Abstract 234).
14. Brimacombe J, Keller C, Fullekrug B, et al.: A multicenter study comparing the Proseal and Classic laryngeal mask airway in anesthetized, nonparalyzed patients. Anesthesiology2002; 92:289--95.
15. Brimacombe JR, Berry A: The incidence of aspiration associated with the laryngeal mask airway: A metaanalysis of published literature. J Clin Anesth 1995; 7:297--305.
16. Farmery AD, Roe PG: A model to describe the rate of oxyhaemoglobin desaturation during apnoea. Br J Anaesth 1996; 76:284--91.
17. Nydahl PA, Axelsson K: Venous blood concentration of lidocaine after nasopharyngeal application of 2% lidocaine gel. Acta Anaesthesiol Scand 1988; 32:135--9.

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