Cardiovascular Effects of Sedative Infusions of Propofol and Midazolam after Spinal Anaesthesia

Abstract

The cardiovascular effects of intravenous sedation were studied in fifty patients after spinal anaesthesia for lower limb or pelvic surgery. Twenty patients received propofol (mean dosage 74 (SD 4) μg/kg/min for 0–20 minutes and 51 (SD 7) μg/kg/min for 20–40 minutes), twenty received midazolam (35 μg/kg + 2.54 (SD 0.2) μg/kg/min for 0–20 minutes and 1.35 (SD 0.2) μg/kg/min for 20–40 minutes) and ten patients received saline infusion only. The forearm vasoconstriction in response to the spinal anaesthesia was measured by strain gauge plethysmography. Spinal anaesthesia lowered systolic and diastolic blood pressure by 18 (SED 4) mmHg and 9 (SED 2) mmHg respectively. (SED = standard error of the difference.) This was associated with a 32% decrease in mean forearm blood flow. Propofol and midazolam caused similar additional reductions in systolic and diastolic blood pressure (10 (SED 4) mmHg and 4 (SED 2) mmHg) and a decrease in heart rate (P< 0.005), but forearm vasoconstriction was not altered. In the control group, however, forearm vasoconstriction increased during 40 minutes in theatre (P<0.05). Recovery from propofol was far more rapid than after midazolam and was virtually complete in ten minutes. This was reflected by an increase in blood pressure and in forearm vasoconstriction in the recovery period.