Effects of sedation with midazolam or propofol infusion on stress hormone and heart rate variability in spinal anesthesia

Objective: Sedation with midazolam or propofol have effects on sympathetic and parasympathetic activity during spinal anesthesia by removing the factor of anxiety and stress. The present study was conducted to compare the effects of sedation with midazolam and propofol on cardiac sympathetic and parasympathetic activity as well as stress hormone in patients having spinal anesthesia. Methodology: This randomized controlled non-blind study was conducted at operating room in the city hospital. Sixty patients, aged 30 to 70 years, with ASA physical status I or II, scheduled for spinal and epidural anesthesia for lower extremity surgery were enrolled for the study. After an epidural catheter insertion, spinal anesthesia was performed at L4/5 with 0.5% tetracaine 8 to 12 mg. Oxygen was administered at 6 L/min by a mask. After surgery started, midazolam infusion was started at 0.6 mg/kg/h for 1.5 min, then changed to 0.15 mg/kg/h, and stopped at the end of surgery in the midazolam group. In the propofol group, propofol infusion was started at 10 mg/kg/h then changed to 5, and 2.5 mg/kg/h every one minute. In the control group, no sedative was administered. Blood pressure, heart rate, respiratory rate, percutaneous oxygen saturation, end-tidal carbon dioxide pressure, sedation level, bispectral index, plasma concentrations of epinephrine, norepinephrine, and cortisol, and hear rate variability were measured. Results: Blood pressure decreased significantly in all groups without any inter group differences. Heart rate decreased significantly in all groups, and the decrease was the largest in the propofol group. Plasma concentrations of epinephrine and norepinephrine decreased significantly in the propofol group. Both high frequency component (HF) and low frequency component (LF)/HF ratio in heart rate variability decreased significantly in all groups. HF and LF/HF were significantly lower in the propofol and midazolam groups than those in the control group. LF/HF was significantly lower in the propofol group than that in the midazolam group. Conclusion: Spinal anesthesia decreased cardiac sympathetic and parasympathetic activity with larger decrease in sympathetic activity. Sedation with continuous infusion of midazolam or propofol further decreased these activities, with propofol exerting a more pronounced effect as compared to midazolam.