Utilizing heart rate variability: Midazolam prevents the sympathovagal imbalance caused by fentanyl/propofol induction

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Context Heart rate variability (HRV) can monitor cardiac autonomic control. Sympathovagal imbalance is expected after fentanyl/propofol induction. Aim The aim of the study was to investigate the effects of intravenous midazolam on HRV and whether it prevents the sympathovagal imbalance caused by fentanyl/propofol induction. Settings and design This is a controlled, randomized, double-blinded study. Patients and methods The study included 50 patients undergoing knee arthroscopies under general anesthesia. Powers of low-frequency (LF: 0.04-0.15 Hz) and high-frequency (HF: 0.15-0.4 Hz) components of HRV, total power (TP), and LF/HF ratio were recorded using MemCalc software. Patients received midazolam 0.05 mg/kg (midazolam group) or an equivalent volume of normal saline (control group), followed by fentanyl 1 mcg/kg and then propofol 2 mg/kg intravenously. Statistical analysis The Mann-Whitney U-test and two-way repeated analysis of variance, followed by Bonferroni correction as a post-hoc test, were used to analyze the data. Results Midazolam induced significant decrease in TP and HF powers, with unchanged LF power and LF/HF ratio. Fentanyl induced significant decrease in TP and LF powers with unchanged HF power and LF/HF ratio in both groups. Propofol induced a significant decrease in TP, HF, and LF powers in both groups. Propofol decreased the LF/HF ratio significantly in the control group but not in the midazolam group. Conclusion Midazolam premedication induced significant decrease in TP and HF powers without changes in LF power or LF/HF ratio. When fentanyl and propofol were given, midazolam was capable of modulating the net effects of both drugs on the HRV by minimizing the decrease in LF power to keep the LF/HF ratio unchanged. This modulatory effect of midazolam works in favor of maintaining the sympathovagal balance.