Flumazenil antagonism of midazolam-induced respiratory depression

Flumazenil, a benzodiazepine antagonist, reliably reverses midazolam-induced sedation, but its effect on respiratory depression has not been clarified completely. Ten healthy male volunteers received midazolam 0.1 mg·kg^-1. Then they received flumazenil 0.5 mg (n = 9) and 1.0 mg (n = 1), intravenously. Ribcage (RC) and abdominal wall (ABD) movement was measured by mercury-insilastic strain gauge. Nasal air flow (FLOW), genioglossal electromyogram (EMG) and oxygen saturation (Sa(O₂)) were recorded simultaneously. Midazolam caused significant increases of RC movement and respiratory rate, and decreases of ABD movement, FLOW, EMG and Sa(O₂). After administration of flumazenil, although respiratory rate returned to the pre-midazolam values, RC movement decreased on the contrary. ABD movement, FLOW, EMG, Sa(O₂) did not recover to the pre-midazolam values. These data suggest that flumazenil 0.5 mg reverses midazolam-induced sedation completely, but is partially effective for some parameters related to respiratory depression.