In order to predict difficult mask ventilation or difficult endotracheal intubation, each patient receiving anesthetic care should have a comprehensive airway history and physical examination performed (also see Chap. 8). Patients should be queried about airway complications that occurred during past anesthetics. A history of trauma during previous airway management to the patient’s lips, teeth, gums, or mouth may indicate the presence of a difficult airway. Similarly, if the patient reports that many attempts were made to “insert the breathing tube” or that he or she was “awake” during previous intubations, a difficult airway should be considered. Medical conditions that classically may portend a difficult airway include a recent or remote history of facial trauma or surgery, obstructive sleep apnea, rheumatoid arthritis, pregnancy, epiglottitis, previous cervical fusion, neck masses, Down’s syndrome, and other genetic syndromes such as Treacher-Collins and Pierre-Robin that have associated facial abnormalities. With a positive history, documentation regarding previous airway management should be reviewed.
Multiple physical examination features have been correlated with a difficult airway (see Table 9.1).
Table 9.1
Components of the preoperative airway physical examination
Component | Nonreassuring finding |
|---|---|
Length of upper incisors | Relatively long |
Relation of maxillary and mandibular incisors during normal jaw closure | Prominent “overbite” (maxillary incisors anterior to mandibular incisors) |
Relation of maxillary and mandibular incisors during voluntary protrusion of the jaw | Patient’s mandibular incisors anterior to (in front of) maxillary incisors |
Inter-incisor distance (mouth opening) | <3 cm |
Visibility of uvula | Not visible when tongue is protruded with patient in sitting position (e.g., Mallampati class >II) |
Shape of palate | Highly arched or narrow |
Compliance of submandibular space | Stiff, indurated, occupied by mass, or non-resilient |
Thyromental distance | <3 finger breadths or 6–7 cm |
Length of neck | Short |
Thickness of neck | Thick (neck size > 17 in.) |
Range of motion of head and neck | Patient cannot touch tip of chin to chest or cannot extend neck |
Every patient receiving anesthetic care should be thoroughly examined for the presence of these features. An adequate exam is difficult to accomplish without active participation and cooperation of the patient. That is, examinations performed solely by inspection may not only be incomplete, but may also be inaccurate. The most common examination performed to evaluate patients for the presence of a difficult airway is determination of what is known as the Mallampati Class. This classification system, first developed in 1985, seeks to predict difficult intubation by functionally assessing the ratio of the size of one’s tongue to the size of one’s oral cavity (see Fig. 9.2).
Figure 9.2
Modified Mallampati classification system (Samsoon and Young)
Increasing difficulty with direct laryngoscopy has been correlated with Mallampati Class III and IV examinations. Although a single worrisome predictor of difficult airway management may be clinically important, a richer and more predictive exam is obtained by screening for multiple predictors in every patient.
Mask Ventilation
Face mask ventilation is the most basic airway management intervention and is the first skill any student of anesthesia should seek to develop. Three goals need to be achieved for optimal facemask ventilation:
1.
An optimal seal must be made between the mask and the patient’s face
2.
The patient’s oropharynx must be opened by anterior displacement of the mandible into the facemask and extension of the head as seen in Fig. 9.3. Placement of an oral or nasal airway during facemask ventilation may assist in opening the oropharynx by creating an artificial passage for gases between the tongue and the posterior pharyngeal wall as seen in Fig. 9.4.
Figure 9.3
Optimal facemask ventilation
3.
Sufficient positive pressure must be generated to overcome the resistance of the patient’s upper airway, chest wall, and diaphragm to effect efficient gas exchange at the alveoli.
Mask ventilation can be employed to augment patient’s spontaneous tidal volumes as a temporizing measure before definitive airway management occurs via endotracheal intubation – as in the case of an intensive care unit patient slowly succumbing to respiratory failure from pneumonia. In the operating room, mask ventilation is most commonly employed to oxygenate and ventilate patients who are apneic from general anesthetic induction agents.
Laryngeal Mask Airway
The laryngeal mask airway (LMA) was first introduced in the United States in 1988 and FDA approved in 1991. The soft plastic device, seen in Fig. 9.5, has revolutionized the care of patients receiving general anesthesia who do not require endotracheal intubation. The device largely supplanted the delivery of facemask anesthesia and has also reduced the rate of endotracheal intubation. The most recent version of the American Society of Anesthesiologists Difficult Airway Algorithm (see Appendix A) places special significance on the use of the LMA in situations where mask ventilation is difficult.
