Surgical stress index reflects surgical stress in gynaecological laparoscopic day-case surgery

Background. Monitoring of analgesia remains a challenge during general anaesthesia. The surgical stress index (SSI) is derived from the photoplethysmographic waveform amplitude and the heart beat-to-beat interval. We evaluated the ability of SSI to measure surgical stress in patients undergoing gynaecological laparoscopy. Our hypothesis was that while keeping State Entropy(TM) (SE) at a predetermined level, SSI would be higher in patients receiving a beta-blocking agent (esmolol) than in those receiving an opioid (remifentanil) during laparoscopy. Methods. Thirty women undergoing gynaecological laparoscopy were assigned randomly to receive esmolol (n=15) or remifentanil (n=15). Anaesthesia was induced with propofol and fentanyl and maintained with desflurane and nitrous oxide 50% in oxygen to keep SE at 50(5). The infusion of esmolol or remifentanil was started before laparoscopy and adjusted to keep the systolic blood pressure at -20 to +10% from the preoperative value. Results. During the fentanyl phase, before surgery, both groups behaved similarly, with an increase in SSI after intubation. In the patients receiving esmolol, the SSI reacted to the initial incision (P<0.05), and remained high after trocar insertion (P<0.05). In patients receiving remifentanil, it did not react to the initial incision, but increased after trocar insertion (P<0.05), and it remained lower both after incision (P<0.05) and after trocar insertion (P<0.05). Conclusion. SSI was higher in patients receiving esmolol. The index seems to reflect the level of surgical stress and may help guide the use of opioids during general anaesthesia.