EFFECTS OF MIDAZOLAM ON HEART-RATE-VARIABILITY DURING SURGERY UNDER SPINAL-ANESTHESIA

Effects of midazolam on the cardiac autonomic nervous system were stud ied by power spectral analysis of electrocardiographic R-R intervals i n patients undergoing elective lower abdominal surgery under spinal an aesthesia. Patients,cere randomly assigned into two groups: 10 patient s in group A received spinal anaesthesia only and 10 in group S receiv ed spinal anaesthesia and midazolam of 0.05 mg/kg when surgery started rn the frequency domain power spectra, low (Lo; 004-0.15 Hz) and high (Hi; 0.15-0.40 Hz) frequency components, were integrated to ascertain sympathetic and parasympathetic activity, respectively There was no i ntergroup difference in starring time of surgery, ventilatory frequenc y, arterial pressure, heart rate, mean and variance of R-R interval, a nd cephalad level of analgesia. In spectral component, Lo decreased (P <0.05) and Hi/Lo ratio increased (P<0.05) relative to their baselines in group S These were also different from group A (P<0.05). We conclud ed that intravenous midazolam depressed sympathetic activity to produc e a vagotonic cardiac autonomic nervous system under spinal anaesthesi a.