Virtual Disaster Medicine

Training Center (VDMTC)

Module 12

The American Society of Anesthesiologists' Management

of the Difficult Airway Algorithm and Explanation-Analysis of the Algorithm

The ASA Algorithm on the Management of the Difficult Airway

THE ANESTHETIZED PATIENT WHOSE TRACHEA IS DIFFICULT TO INTUBATE

There are three general situations in which an anesthesiologist will be required to intubate the trachea of an unconscious or anesthetized patient whose airway is difficult to manage.  First, the patient may already be unconscious (e.g., posttrauma) or anesthetized (e.g., drug overdose).  Second, the patient may absolutely refuse or not tolerate awake intubation (e.g., a child, a mentally retarded patient, or an intoxicated combative patient [see dashed line, Fig. 3]).  Third, and perhaps most commonly, the anesthesiologist may fail to recognize intubation difficulty on the preoperative evaluation.  Of course, even in the first and second situations above, the preoperative airway evaluation is very important because the findings may dictate the choice of intubation technique.  In all three of the situations above, the patient may, in addition, have a full stomach.

All of the intubation techniques that are described for the awake patient^2,10 can be used in the unconscious or anesthetized patient without modification.  However, direct and fiberoptic laryngoscopy may be slightly more difficult in the paralyzed, anesthetized patient compared to the awake patient because the larynx may become more anterior relative to other structures due to relaxation of oral and pharyngeal muscles.⁴⁹  In addition, and more importantly, the upper airway structures may coalesce into a horizontal plane instead of separating out in a vertical plane.^29,48

In the anesthetized patient whose trachea has proven to be difficult to intubate, it is necessary to try to maintain gas exchange between intubation attempts by mask ventilation and also during intubation attempts, whenever possible.  As depicted in the latest version of the Difficult Airway Management Algorithm, opportunities to deliver supplemental oxygen throughout whatever steps are taken to secure the airway, should be pursued.⁴⁷  Positive pressure ventilation may be continuously maintained during fiberoptic endoscopy-aided orotracheal intubation by using an anesthesia mask that has a special fiberoptic instrument port, which is covered by a self-sealing diaphragm (instead of standard mask) along with an airway intubator (instead of the standard oropharyngeal airway) (see Chapter 18)^45,48 or by using an LMA as a conduit for the FOB (see Chapter 21).⁹

It is extremely important to realize that the amount of laryngeal edema and bleeding will very likely increase after every forceful intubation attempt.  Although laryngeal edema and bleeding can occur with any intubation method, it is most common after use of a laryngoscope or retraction blade.  Consequently, if there does not appear to be anything really new or different that can be atraumatically and quickly tried (better sniffing position, external laryngeal manipulation, new blade, new technique, much more experienced laryngoscopist, etc.) after a few failed intubation attempts, and ventilation by mask can still be maintained, it is prudent to cease intubation attempts, and consider the following options:1) awaken the patient, 2) continue anesthesia via mask or LMA ventilation, or 3) perform a tracheostomy or cricothyrotomy before the ability to ventilate the lungs via mask is lost (Figs. 1a and 1b).  In fact, the most common scenario in the respiratory catastrophes in the ASA closed-claims study was the development of progressive difficulty in ventilating via mask between persistent and prolonged failed intubation attempts; the final result was inability to ventilate via mask and provide gas exchange (see Chapter 53).¹⁹  If the surgical procedure is not urgent, awakening the patient and doing the procedure another day will allow for better planning.  On the other hand, “awakening the patient” is often not possible in a failed airway situation, especially if the intubation is emergent.  Many cases may be done (and may have to be done) via mask or LMA ventilation (e.g., cesarean section) if ventilation is reasonably easy.  Finally, in some cases, the airway will have to be secured by a tracheostomy or cricothyrotomy (e.g., thoracotomy, intracranial-head-neck cases, and cases in the prone position).

If regurgitation or vomiting occurs at any time during attempts at endotracheal intubation in an anesthetized patient, there are a number of therapeutic steps that should be taken.  First, the patient should be put in the Trendelenburg position, and the head, and perhaps the body, turned to the left.  Second, the mouth and pharynx should be suctioned with a large bore suction device.  Endotracheal intubation may then be tried with the patient in the lateral position; the advantage of this maneuver is that the tongue may be more out of the way, but the disadvantage is that this intubation position may be unfamiliar to most anesthesiologists.  If the ET has been passed into the esophagus, it may be left there; the advantage is that the ET may decompress the stomach and perhaps guide (by negative example) future intubation attempts.  However, the disadvantage is that it may be more difficult to obtain a satisfactory mask seal between intubation attempts, even if the esophageal ET is sharply bent off to the side by the rim of the mask.  Once the airway is secured and aspiration of gastric contents has been performed, standard treatment consists of suctioning, mechanical ventilation, positive end-expiratory pressure, fiberoptically guided saline lavage, and perhaps steroids and appropriate antibiotics after specific cultures and sensitivities are available (see Chapter 32).

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