What are the predictors of difficult mask ventilation?
One of the most important predictors of the difficult air-way is a history of difficult airway. The opposite is not neces-sarily true. A history of problem-free airway management is suggestive of future ease, but not a guarantee. Many factors that contribute to difficulty are progressive. Examples of such problems include rheumatoid arthritis and obesity. An airway history should be elicited from all patients. Review of prior anesthesia records is frequently helpful. They may describe previously encountered problems, failed therapies, and successful solutions.
Difficult facemask ventilation occurs when a practi-tioner cannot provide sufficient gas exchange due to inad-equate mask seal, large volume leaks, or excessive resistance to the ingress or egress of gas. This occurs with an incidence of 0.08–5%. The wide range is probably due to conflicting definitions of difficult mask airway. Risk factors for difficult mask ventilation include full beard, massive jaw, edentulousness, skin sensitivity (burns, epidermolysis bullosa, fresh skin grafts), facial dressings, obesity, age greater than 55 years, and a history of snoring. Other criteria that suggest the possibility of difficult facemask ventilation include large tongue, heavy jaw muscles, history of obstructive sleep apnea, poor atlanto-occipital extension, some types of pharyngeal pathology, facial burns, and facial deformities. Multiple types of pharyngeal problems can produce difficult facemask ventilation. They include lingual tonsil hypertrophy, lingual tonsillar abscess, lingual thyroid, and thyroglossal duct cyst. Many of these cannot be diagnosed by classical airway examination techniques. The presence of any one factor is suggestive of difficult mask ventilation. The more factors present at the same time, the greater the likelihood of difficulty. Increased mandibulo-hyoid distance has been associated with obstructive sleep apnea, the pathophysiology of which may be related to difficult mask ventilation.
Traditional facemask airway management is generally safe and effective. In the unusual instances when it is not, tracheal intubation remains the fallback option. Although this scheme works well in most cases, approximately 15% of difficult intubations are also difficult mask airways.