Effect of conscious sedation on cardiac autonomic regulation during colonoscopy

Background: Colonoscopy is associated with cardiovascular events including hypotension, hypertension, and myocardial ischemia. The pathogenetic mechan isms of these cardiovascular events are unknown, but there is evidence that the autonomic nervous system may play a role. Conscious sedation is often used to relieve the inconvenience caused by the procedure. In this study, w e evaluated the effects of sedation on cardiac autonomic regulation during colonoscopy. Methods: One hundred and eighty patients undergoing elective c olonoscopy were prospectively randomized into three groups: (i) sedation wi th intravenous midazolam (midazolam group); (ii) sedation with intravenous saline (placebo group); and (iii) no intravenous cannula (control group). C ontinuous electrocardiogram was recorded prior to, during, and after the co lonoscopic procedure. Heart rate variability (HRV) was assessed by means of the power spectral analysis; the powers of low-frequency (LF 0.04-0.15 Hz) and high-frequency (HF 0.15-0.40 Hz) components were calculated. Results: Intubation of the colonoscope increased the LF component of HRV and decreas ed HF power in all study groups compared to baseline recording. Furthermore , compared to baseline, the LF/HF ratio-a marker of cardiac sympathetic reg ulation-increased during intubation in the midazolam (P < 0.001) and placeb o (P < 0.05) groups, with no change in the control group. During intubation the midazolam group presented with higher LF and lower HF power than place bo (P < 0.001) and control groups (P < 0.01). Accordingly, the LF/HF ratio was higher in the midazolam group than in the placebo (P < 0.05) or control groups (P < 0.05). Conclusions: Midazolam potentiates the dominance of the sympathetic nervous system induced by colonoscopy. Therefore, conscious se dation with midazolam may contribute to the occurrence of cardiovascular ev ents during colonoscopy.