Time course of ventilatory response to carbon dioxide after intravenous diazepam

Dual isohypercapnic studies on the time course of depression following intravenous diazepam permit detailed analysis of changes in the ventilatory response to carbon dioxide. The mean slope of the CO2 response curves of eight healthy volunteers dropped from 2.38 to 1.21 1 . min-1 . mmHg-1 ( P less than 0.05) within three minutes after injection of diazepam 0.4 mg/kg. Twenty-five minutes after injection, the slope was only 1.49 1 . min-1 . mmHg-1, still significantly lower than control (P less than 0.05). At 30 min, the slope has increased to 1.73 1 . min-1 . mmHg-1 and was no longer different from control at the 0.05 level of significance. There was also a significant correlation between the slope of the CO2 response curve and level of consciousness (r = 0. 81). There was little or no displacement of the response curve at any selected ventilation except as accounted for by the slope change. The authors conclude that ventilatory depression resulting from intravenous diazepam begins within one minute and lasts at least 25 min after injection.