We studied electromyography (EMG) of the geniohyoid muscle (Gh) and diaphragm (Di) in 12 postoperative, premedicated (flunitrazepam 2 mg PO), asymptomatic patients who snored after recovering from general anesthesia, the induction of which was partly achieved by i.v. midazolam. After extubation of the trachea, integrated EMG activity of Gh (E-Gh(MTA)) and Di (E-Di(MTA)) were measured. For Gh, tonic and phasic activity were distinguished. Patients were studied during obstructive apnea, at the end of apnea, while breathing through an artificial Guedel airway, and during quiet breathing 5 min after flumazemil. All patients experienced episodes of postoperative upper airway obstruction and nine became apneic. Flumazenil restored consciousness and predominant tonic E-GhMTA associated with upper airway patency in all patients. Reduced tonic E-GhMTA characterized postoperative obstructive apnea. Resolution of apnea required a burst of both tonic and phasic E-GhMTA associated with intense E-Di(MTA). Breathing through the Guedal airway resulted in patent airway in 8 of 10 patients and was associated with low tonic and phasic E-GhMTA and reduced E-Di(MTA). In this study, we demonstrated that the tonic pharyngeal muscular support modulates airway patency in the postoperative period. Because it is reversed by flumazemil, benzodiazepines are certainly the main cause of airway obstruction in these patients.
Implications: Upper airway obstruction during recovery from general anesthesia induced by i.v. midazolam is associated with low tonic pharyngeal muscular support, which modulates upper airway patency in the postoperative period.