Study objective: To determine the improvement in laryngoscopic view obtained using both the Macintosh and Miller blades by applying optimal external laryngeal manipulation (OELM).
Design: Prospective, with each patient serving as his or her own control.
Setting: Inpatient operating rooms of a University Medical Center.
Patients: 181 informed and consenting adult nonpregnant patients requiring general anesthesia and tracheal intubation. The only exclusion criteria was the need to apply cricoid pressure to prevent aspiration of gastric contents.
Interventions: Anesthetized, paralyzed patients underwent laryngoscopy without external laryngeal manipulation and the laryngoscopic view was graded ("A") according to visualized structures [1.0-1.9 = all (1.0) or part of the vocal cords (90% = 1.1 and 10% = 1.9); 2 = just the arytenoids; 3 = just the epiglottis; 4 = just the soft palate]. The larynx was then quickly manipulated by the thumb and index and middle fingers of the laryngoscopist's right hand in both cephalad and posterior directions over the hyoid, thyroid, and cricoid cartilages until it was determined which vector and spot produced the optimal laryngoscopic view ("B").
Measurements and main results: It was found that in every patient with a "A" greater than 1.0, OELM improved the view; i.e., "B" decreased relative to "A." For both the Macintosh blade patients and Miller blade patients with an "A" equal to 2, "B" decreased by one whole laryngoscopic grade in all patients. For both the Macintosh and Miller blade patients with an "A" equal to 3, "B" decreased by at least one whole laryngoscopic grade in all patients and by two laryngoscopic grades in most patients. No patient had an "A" equal to 4. The distribution of optimal-external-laryngeal-manipulation (OELM) spots for all patients was 1%, 40%, 48%, and 11% for the hyoid, high thyroid, low thyroid, and cricoid cartilages, respectively, and the distribution was not significantly different for either the Macintosh and Miller blade groups or for the "A" and "B" subgroups (i.e., "A" < 1.9, = 2 or = 3).
Conclusions: We conclude that OELM can improve the laryngoscopic view by at least one whole grade, that the best way to determine OELM for an individual patient is on an empirical basis by manipulation of the larynx with the laryngoscopist's right hand, and that OELM should be an instinctive and reflex response to any "A" of 2, 3, or 4.