SYMPATHOVAGAL EFFECTS OF SPINAL-ANESTHESIA ASSESSED BY THE SPONTANEOUS CARDIAC BAROREFLEX

Background: The changes in sympathovagal balance induced by spinal ane sthesia remain controversial. The spontaneous baroreflex method allows the continuous assessment of the spontaneous engagement of the cardia c baroreflex, giving an index of sympathovagal balance. The purpose of this study was to follow the effects of spinal anesthesia on spontane ous baroreflex sensitivity. Methods: Continuous electrocardiogram and noninvasive blood pressure were recorded in 24 patients scheduled for elective inguinal hernia repair and randomly assigned to three groups: (1) no volume loading, (2) volume loading of 15 ml/kg lactated Ringer 's solution, and (3) continuous infusion of etilefrine (an ephedrine-l ike drug). Each patient was studied before, during, and after bupivaca ine-induced spinal anesthesia (mean sensory block: T4). Spontaneous ba roreflex sensitivity and parameters of time-domain analysis of heart r ate variability were calculated from 30 min of recording of each perio d. Results: No significant change in spontaneous baroreflex slope or p arameters of time-domain analysis were observed after regional anesthe sia in any group. However, three patients experienced episodes of brad ycardia and hypotension in the absence of a high block; these three pa tients showed an increase in spontaneous baroreflex sensitivity and ti me-domain parameters. Conclusions: Using a noninvasive, continuous tec hnique ro estimate cardiac sympathovagal balance, no significant varia tion in autonomic balance induced by spinal anesthesia was observed. H owever, untoward episodes of bradycardia and hypotension occurred in t hree patients, who could not be prospectively identified by the parame ters studied. (Key words: Anesthesia technique: spinal. Anesthetic, lo cal: bupivacaine. Autonomic nervous system: sympathovagal balance. Mea surement techniques: electrocardiography; heart rate).