• Riccardo Colombo, Ferdinando Raimondi, Alberto Corona, Ilaria Rivetti, Federica Pagani, Vanessa Della Porta, and Stefano Guzzetti.
• From the Anaesthesiology and Intensive Care Unit (RC, FR, AC, IR, FP, VDP); Accident and Emergency Department, Azienda Ospedaliera Luigi Sacco, Milan, Italy (SG).
• Eur J Anaesthesiol. 2014 Feb 1;31(2):76-84.

BackgroundSurgical plethysmographic index (SPI) has been proposed as a tool to measure the nociception/antinociception balance during general anaesthesia. Untreated nociception may increase sympathetic tone, but the relationship between SPI and the autonomic nervous system (ANS) is poorly understood.ObjectiveWe hypothesised that two different levels of SPI might be associated with differences in ANS modulation, measured by the frequency domain analysis of heart rate variability (HRV).DesignA randomised, cross-over group study, conducted between February and November 2009.SettingUniversity tertiary referral hospital in Milan, Italy.PatientsForty-two adult patients undergoing scheduled laparoscopic abdominal surgery.InterventionsECG, noninvasive arterial blood pressure and SPI were recorded during balanced general anaesthesia with inhaled sevoflurane and intravenous remifentanil. After pneumoperitoneum induction, the remifentanil infusion rate was set to obtain two different levels of SPI (>50, HI-SPI, and <50, LO-SPI) for each patient.Main Outcome MeasuresArterial pressure, heart rate (HR), low-frequency and high-frequency spectral components, the low frequency/high frequency ratio (measure of sympathovagal balance) and whole power spectrum density of HRV were measured at the two different levels of SPI.ResultsThirty-nine patients were included in the final analysis. During LO-SPI, HR and systolic and mean blood pressures were significantly lower than HI-SPI. The median low frequency/high frequency ratio was reduced during LO-SPI [1.29 interquartile range (IQR) 0.66 to 2.05) vs. 2.36 (1.30 to 3.62), P = 0.008]. The sensitivity analysis revealed a significant correlation between SPI changes and changes of all ANS indices, arterial pressure and HR, with a slightly better correlation for low frequency/high frequency (Spearman ρ = 0.70, IQR 0.484 to 0.834, P < 0.001).ConclusionIn the context of a balanced general anaesthesia in healthy patients undergoing laparoscopic abdominal surgery, ANS modulation seems to correlate with changes in SPI. Further studies are warranted to assess whether this may reflect a change in nociception/antinociception balance or a pharmacodynamic effect of remifentanil.

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