Objective: The Analgesia Nociception Index (ANI) monitor measures the relative parasympathetic tone as a surrogate for the antinociception/nociception balance during general anesthesia. The aims of this observational study were to test whether ANI could early detect hemodynamic reactivity (HemodR) during propofol anesthesia, measure pain in conscious patients after surgery, and determine ANI predictive thresholds.
Materials and methods: After institutional approval and informed consent, adult patients scheduled for total knee replacement were included. Propofol was administered using a target-controlled infusion device, and sufentanil was administered at induction and in case of "HemodR," defined as a 20% increase in heart rate or systolic blood pressure. Data were collected before the start of surgery (NoStim), in case of "HemodR," and after awakening before and after the pain had been treated by truncular analgesia. Nonparametric tests were conducted. Thresholds were determined using an receiver operating characteristic analysis. Results are presented as median (interquartile range).
Results: A total of 27 patients have been analysed. ANI decreased from 82 (30) at "NoStim" to 47 (22) at "HemodR," whereas heart rate increased moderately from 61 (14) to 65 (18) and systolic blood pressure increased significantly from 91 mm Hg (16 mm Hg) to 151 mm Hg (25 mm Hg). Receiver operating characteristic analysis led to a threshold of 63 for "HemodR" detection (sensitivity=80%, specificity=88%, area under the curve=0.92), whereas ANI performance in awake patients was lower.
Discussion: ANI measures during propofol anesthesia are coherent with the evolution of the analgesia/nociception balance, although its performance decreases in awake patients. Further clinical validation should focus on demonstrating the benefit of maintaining ANI over 63 during surgery.