The effects of speed of injection on induction with propofol. A comparison with etomidate.

One hundred and eighty female patients received either propofol 2.5 mg/kg or etomidate 0.3 mg/kg injected over 20, 40 or 80 seconds for induction of anaesthesia after premedication with temazepam 20 mg. The mean induction times for both etomidate and propofol were significantly reduced with increasing speed of injection. The mean induction times for etomidate were significantly less than propofol at the slower rates of injection. At each speed of injection, the decrease in systolic, mean and diastolic arterial blood pressures with etomidate were less than with propofol. The decrease in systolic blood pressure was not significantly affected by injection speed for either drug. Apnoea occurred significantly more frequently with propofol than with etomidate at each speed of injection and the incidence of apnoea greater than 60 seconds with propofol was significantly higher when injected over 20 seconds than 80 seconds. The incidence of pain on injection was unaffected by injection speed for either drug. The incidence of myoclonus and (or) hypertonus was significantly higher following etomidate.