Cardiac sympathovagal balance and peripheral sympathetic vasoconstriction: epidural versus general anesthesia

Both epidural and general anesthetics alter autonomic balance. However, the relative differences between epidural (EA) and general anesthetics (GA) with regard to cardiac and peripheral sympathovagal balance have not been described. Twenty consecutive patients scheduled for radical retropubic prostatectomy were randomized to receive EA (n = 10) or GA (n = 10). Power spectral analysis was performed on the electrocardiographic recordings, with the ratio of low (0.05-0.125 Hz)/high (0.125-0.5 Hz) frequency power used an index of cardiac sympathovagal balance. The forearm minus fingertip skin-surface temperature gradient (> 4 degrees C) was used as an indicator of sympathetically mediated peripheral vasoconstriction. Patients in the EA group demonstrated a significantly greater low/high frequency power ratio and a more frequent incidence of peripheral vasoconstriction than the GA group during the intraoperative period. During the postoperative period, the GA group demonstrated an increase in the low/high ratio and the incidence of vasoconstriction relative to the intraoperative period. Intraoperatively, upper body vasoconstriction appears to be accompanied by a significant shift in cardiac sympathovagal balance toward sympathetic predominance with EA relative to GA. Postoperatively, GA is associated with a shift in the sympathovagal balance toward sympathetic predominance. Further research is required to determine whether this results in cardiovascular compromise in the high-risk patient.