BACKGROUND: Maintaining a balance between nociception and analgesia perioperatively reduces morbidity and improves outcomes. Current intraoperative analgesic strategies are based on subjective and nonspecific parameters. The high-frequency heart rate (HR) variability index is purported to assess the balance between nociception and analgesia in patients under general anesthesia. This prospective observational study investigated whether intraoperative changes in the high-frequency HR variability index correlate with clinically relevant nociceptive stimulation and the addition of analgesics. METHODS: Instantaneous and mean high-frequency HR variability indexes were measured continuously in 79 adult subjects undergoing general anesthesia for laparoscopic cholecystectomy. The indexes were compared just before and 2 minutes after direct laryngoscopy, orogastric tube placement, first skin incision, and abdominal insufflation and just before and 6 minutes after the administration of IV hydromorphone. RESULTS: Data from 65 subjects were included in the final analysis. The instantaneous index decreased after skin incision ([SEM], 58.7 [2.0] vs 47.5 [2.0]; P < .001) and abdominal insufflation (54.0 [2.0] vs 46.3 [2.0]; P = .002). There was no change in the instantaneous index after laryngoscopy (47.2 [2.2] vs 40.3 [2.3]; P = .026) and orogastric tube placement (49.8 [2.3] vs 45.4 [2.0]; P = .109). The instantaneous index increased after hydromorphone administration (58.2 [1.9] vs 64.8 [1.8]; P = .003). CONCLUSIONS: In adult subjects under general anesthesia for laparoscopic cholecystectomy, changes in the high-frequency HR variability index reflect alterations in the balance between nociception and analgesia. This index might be used intraoperatively to titrate analgesia for individual patients. Further testing is necessary to determine whether the intraoperative use of the index affects patient outcomes.