[Relationship between laryngoscopy degree and intubation difficulty]

To determine the relation between difficult intubation and grade of direct laryngoscopy, as well as the factors that influence them, and prognosis.

In 1,336 patients receiving general anesthesia, seven airway measurements were made to reflect degree of difficulty and predictive value of presurgical tests on direct laryngoscopy and intubation.

The incidences of difficult laryngoscopic and intubation procedures were 1.4 and 3.0%, respectively. Difficult intubation was more frequent in women and in patients between 40 and 65 years of age (p < 0.05). In 105 intubations (64.8%) performed with moderate difficulty (use of a stylette, external laryngeal pressure or two tries) and 17 (41.5%) performed with difficulty (three or more tries), the laryngoscopic procedure was graded as easy (Cormack-Lehane grade I-II). In these cases (easy laryngoscopy with moderate/difficult intubation), the causes recorded were size of endotracheal tube in comparison with the laryngeal opening (n = 11); anterior glotis (n = 36); insufficient relaxation (n = 31); disease in or beyond the vocal cords (n = 29); or undetermined (n = 15). In the easy intubation cases, the laryngoscopic procedures were grade III in 2.9%. Intubation was difficult in 16.3% (n = 39) of patients presenting some type of abnormality upon examination of the airway (p < 0.05). The airway characteristic that best predicted laryngoscopic difficulty was extension of the lower neck to 90 degrees (relative risk of 4.46), mouth opening less than 3.5 cm (3.92), presence of two airway abnormalities (4.25) and presence of three or more abnormalities (5.39) (p < 0.01).

The fact that cases of easy laryngoscopy coincide with difficult intubation suggests that, to the degree of intubation difficulty must be added extrinsic factors (individual skill, maneuvers performed, instrumentation, relaxation of the laryngeal musculature and others) that are hard to standardize and reflect when predicting an intubation by the grade of difficulty in laryngoscopy.