Background: Surgical noxious stimuli generate a stress response with an increased sympathetic activity, potentially affecting the perioperative outcome. Surgical Pleth Index (SPI), derived from the pulse plethysmogram, has been proposed as a tool to assess nociception-antinociception balance. The relationship between SPI and autonomic nervous system (ANS) during general anesthesia is poorly understood and it is doubtful if SPI-guided analgesia may offer advantages over the standard clinical practice. The study was designed to evaluate if SPI-guided analgesia leads to a lower sympathetic modulation compared with standard clinical practice.
Methods: Electrocardiographic wave, non-invasive blood pressure and SPI were recorded in ASA I-II patients undergoing elective laparoscopic cholecystectomy, randomized to receive SPI-guided analgesia or standard analgesia. Hemodynamic parameters, SPI, mean and variance of heart rate, low (LF) and high frequency (HF) spectral components of heart rate variability were measured at four time points: (T0) baseline, (T1) after induction of general anesthesia, (T2) after pneumoperitoneum insufflation and (T3) after pneumoperitoneum withdrawal.
Results: SPI, hemodynamic and ANS parameters changed significantly in both groups during the study period (P<0.0001). At T2 SPI and markers of sympathetic modulation were significantly lower in SPI group (mean [SD] SPI 38.1 [15.3] vs. 48.1 [16.2] normalized units, P<0.05; LF 38 [8.6] vs. 56.2 [20.6] normalized units, P<0.01; LF/HF 1.01 [1.1] vs. 2.68 [2.07], P<0.01). There was no difference in remifentanil consumption, recovery time from anesthesia, or postoperative pain and complications.
Conclusion: SPI-guided analgesia led to a more stable sympathetic modulation but didn't seem to offer clinically relevant advantages over the standard clinical practice for laparoscopic cholecystectomy.