[Effect of continuous intravenous administration of midazolam and ketamine on respiratory pattern]

The purpose of the study was to investigate the effect of continuous IV administration of midazolam and ketamine on respiratory pattern in six adult volunteers. Midazolam 0.05 mg/kg and ketamine 0.5 mg/kg were given, and then 0.1 mg/kg/hr for midazolam and 1 mg/kg/hr for ketamine were administered continuously. We measured MV, RR and TV (OMR86036), and calculated duty ratio and mean inspiratory flow at the level of 0 and 5 cmH2O CPAP during spontaneous respiration of air with and without 5% CO2. Each parameter was obtained before and 1 hr after the start of IV administration of the drugs. With 5% CO2, MV decreased significantly from 15.5 +/- 1.5 l/min to 11.7 +/- 0.8 l/min at 0 cmH2O CPAP level and from 15.8 +/- 1.8 l/min to 12.6 +/- 1.5 l/min at 5 cmH2O CPAP level, and also mean inspiratory flow decreased significantly from 590 +/- 2 ml/sec to 421 +/- 30 ml/sec at 0 cmH2O CPAP level and from 606 +/- 53 ml/sec to 477 +/- 48 ml/sec at 5 cmH2O CPAP level. TV decreased significantly during sedation at both CPAP levels with or without 5% CO2, while RR and duty ratio tended to increase. It was thought that, when the respiration was stimulated with 5% CO2, the decrease in mean inspiratory flow greatly contributed to the fall in MV during administration of midazolam and ketamine.