The ANI monitor's "Energy" variable detects autonomic state modification during general anesthesia, sedation and...

The Analgesia Nociception Index (ANI) is based on respiratory sinus arrhythmia and is a validated surrogate marker of the nociception-antinociception balance. Along with the ANI, the monitor provides a measure of overall heart rate variability modulation named "Energy" and which is closely related to the standard deviation of normal R-R intervals. The objective of the present study was to evaluate variations in "Energy" during general anesthesia, sedation, and spinal anesthesia. We retrospectively analyzed data stored in the anesthesia data warehouse at Lille University Medical Center (Lille, France). Eligible cases involved general anesthesia, spinal anesthesia, or sedation over the period 2012-2024. Patients with arrhythmia or missing baseline data were excluded. Three periods were defined: pre-induction (P1), post-induction (P2), and intraoperative (P3). Linear mixed models were adjusted for age, the American Society of Anesthesiologists score, norepinephrine use, and sex. 2226 procedures were included. The decrease in "Energy" after induction was significantly greater for general anesthesia after adjustment between P1 and P2 (Mean (SD) -0.306 (-0.321; -0.292), p < 0.001) and between P1 and P3 (-0.334 (-0.348; -0.319), p < 0.001). Same results were found for sedation (P1-P2: -0.120 (-0.176; -0.064), p < 0.001; P1-P3: -0.113 (-0.168; -0.056), p < 0.001) and spinal anesthesia (P1-P2: 0.082 (0.017; 0.146), p = 0.012; P1-P3: 0.089 (0.025; 0.153), p = 0.006) after adjustment. Changes during sedation and spinal anesthesia were not clinically relevant. "Energy" decreases after the induction of general anesthesia and sedation and thus reflects a lower degree of autonomic modulation.