To the Editor:—
We read with great interest the article by Dr. Langeron et al. 1providing the first large study attempting to assess the incidence of difficult mask ventilation and to establish the difficult mask ventilation prediction score. The authors suggest two important factors contributing to difficulty in mask ventilation, which are inability to fit a face mask and inability to overcome obstruction of the upper airway after general anesthesia or muscle relaxation. Unfortunately, the difficult mask ventilation prediction score cannot sufficiently reflect factors related to the latter. The main causes of obstruction of the upper airway are known to be posterior displacement of the base of the tongue or the epiglottis and collapse of the laryngeal inlet. 2–6The jaw-thrust maneuver can lift these tissues and restore airway patency. 2–6Thus, we consider that assessment of ability to thrust the jaw fully is necessary to predict difficult mask ventilation. Calder et al. 7have suggested the mandibular protrusion test. The test evaluates the degree of protrusion of the mandible when the patient protrudes the mandible as far forward as possible. The degree of protrusion is classified as follows: class A: the lower incisors can be protruded anterior to the upper incisors; class B: the lower incisors can be brought edge to edge with the upper incisors but not anterior to them; class C: the lower incisors cannot be brought edge to edge with the upper incisors. This test is simple and has little interobserver variations because there is a clearer endpoint. Although Calder et al. 7have demonstrated that impaired mandibular protrusion is a good predictor of difficult laryngoscopy, we believe that the test may be useful for prediction of difficult mask ventilation.