30.4.1 Is This Patient Predicted to Have a Difficult Airway?
Airway examination should focus on the ability to provide ventilation and oxygenation through a bag-mask, an endotracheal tube, an extraglottic device, and a surgical airway. The mnemonics MOANS, RODS, LEMON, and SHORT described in Chapter 1 provide a useful framework to assess these aspects of the patient's airway. It should be emphasized that while the ASA task force on management of the difficult airway outlined 11 criteria for preoperative airway assessment for laryngoscopy and intubation,15 no single airway test has perfect sensitivity or specificity in predicting difficult laryngoscopic intubation. In general, all single airway predictors share a common set of characteristics: low sensitivity, high specificity, and low positive predictive value. The combination of several airway predictors tends to improve the positive predictive value for difficult laryngoscopic intubation.
With reference to the airway examination presented in Section 30.1 earlier, it is apparent that this patient has several predictors of a difficult laryngoscopic intubation: borderline mouth opening, a reduced thyromental distance, and a Mallampati III classification. In combination, these characteristics place this patient at a moderately high risk for difficult laryngoscopy. However, alternative intubation devices, such as the intubating LMA (ILMA) or lighted stylet should be successful, and with adequate control of secretions, so should flexible or rigid fiberoptic devices or videolaryngoscopes. Bag-mask-ventilation if needed should be possible, although not optimal. Should extraglottic device placement and use be required, decreased pulmonary compliance due to ARDS may present a problem with pop-off leak developing at higher airway pressures: availability of an LMA Pro-Seal or LMA Supreme might be advisable. Cricothyrotomy should be possible. Note that although some of these techniques are not desirable in the patient with SARS, their predicted success must still be assessed, particularly in the patient with predictors of difficulty.
30.4.2 What Do You Do Differently When Establishing an Airway in a SARS Patient?
A SARS patient poses a unique risk to health care workers due to its highly infectious nature and a high mortality rate for those infected. In developed countries such as Canada and Singapore, approximately 50% of SARS cases were health care workers involved in caring for SARS patients. The processes of tracheal intubation, bag-mask-ventilation, and suctioning were associated with the highest risk of acquiring SARS.8-10 A cluster of nine health care workers who cared for a single SARS patient around the time of intubation in the ICU themselves developed SARS.16
In order to minimize the risk of SARS cross-transmission to health care workers, guidelines have been developed to reduce the risk of aerosolization of SARS droplets during the process of intubation.3,17,18 It is critical that the health care worker apply and remove personal protection equipment (see Section 30.5.5) prior to and after intubation. In addition, bag-mask-ventilation, nebulization, and application of topical airway anesthesia are to be avoided. The patient should thus be sedated and paralyzed unless contraindicated. However, if a high potential for difficult laryngoscopy exists, there may be a conflict of priorities.
30.4.3 How Are You Going to Approach This Patient's Airway?
This patient's situation presents us with a real dilemma. On the one hand, an awake intubation following application of topical airway anesthesia is generally considered to be the safest method of securing the airway in the patient presenting with potential difficult laryngoscopic intubation. On the other hand, to minimize the risk to health care personnel of SARS transmission, avoiding BMV is preferred, and paralysis of the patient will help avoid the potential for coughing. Protecting the patient and the health care worker are both important priorities.
Ultimately the method chosen for intubation is determined by how likely one is to encounter a failed airway situation (see Chapter 2). The possibility for such a situation will become evident as the patient is assessed for predictors of difficulty in all aspects of airway management. If the patient presents with evidence that airway control will be difficult using various techniques of endotracheal tube placement, bag-mask-ventilation, an extraglottic device, or cricothyrotomy, the practitioner should accept the risk of disease transmission and perform an awake intubation. However, in this case, as outlined in Section 30.4.1 earlier, the patient presents predictors of only moderate difficulty with laryngoscopy and no predictors of difficulty with alternative intubation (eg, ILMA, lighted stylet, flexible bronchoscope) equipment use. Bag-mask and extraglottic device ventilation, if needed, will most likely be successful in spite of reduced pulmonary compliance. Cricothyrotomy should pose few problems.
Thus, a reasonable Plan A approach in this patient is to attempt tracheal intubation by direct laryngoscopy after induction using short-acting anesthetic and paralytic agents. The intubation should be undertaken by an experienced airway practitioner, wearing full protection, and with a full complement of alternative intubating devices. In addition, an extraglottic rescue device and cricothyrotomy equipment should be readily available in the room.
If direct laryngoscopy fails after one or two attempts, and oxygenation remains acceptable, Plan B calls for an alternative device to be used, in this case a video laryngoscope (eg, Glidescope) or a flexible bronchoscope. If intubation is not successful after three attempts, the patient should be awakened with the intention of proceeding with an awake intubation. If at any time between attempts oxygenation cannot be maintained with bag-mask-ventilation, Plan C calls for the immediate use of an EGD, such as an LMA ProSeal or LMA Fastrach™, while concurrently preparing to perform a cricothyrotomy in this cannot intubate cannot oxygenate situation.