The Effect of Change of Position on Surgical Pleth Index in Patients Undergoing Lumbar Spine Surgery under General Anesthesia

Background: To study the effect of change in position from supine to prone position on surgical pleth index (SPI) under GA. Correlation between SPI and heart rate (HR), mean arterial pressure (MAP), and pulse pressure variation (PPV).

Materials and Methods: After informed written consent, 25 patients undergoing lumbar spine surgery were recruited into study. Patients were connected with ECG, NIBP, SpO2, temperature monitors. Induction was with fentanyl 2 µg/kg, titrated dose of propofol, and vecuronium 0.1 mg/kg. Patient was intubated and ventilated to maintain ETCO2 32 to 35 m Hg. Morphine 0.1 mg/kg was given intravenously. Anesthesia was maintained with propofol TCI pump and fentanyl infusion 1 µg/kg/h to achieve the static entropy of 40 to 60. Arterial line was inserted. HR, MAP, PPV, and SPI were recorded in supine position 0, 5, 10, 15, and 20 minutes after positioning patient in prone at 0, 5, 10,15, and 20 minutes. Additionally, they were recorded at 0, 2, and 5minutes pre- and postskin incision, muscle splitting, and laminectomy. Repeated measures data were analyzed within each time point block and between the time point blocks using linear mixed effect models with random intercept by the subject.

Results: There was significant increase in SPI after positioning the patient in prone position (p ≤ 0.001). There was no significant change in MAP and HR but PPV showed significant change when patients were positioned prone (p = 0.001). Moderate correlation was noted between SPI and MAP. Negative correlation was noted between SPI and PPV.

Conclusions: SPI changes when position is changed from supine to prone. Therefore, interpretation of SPI as a surrogate measure of nociception–antinociception balance could therefore be confounded in various situations.

Publication History

Article published online:
25 March 2020