The Analgoscore: A Novel Score to Monitor Intraoperative Nociception and its Use for Closed-Loop Application of Remifentanil

Abstract

Purpose . Measuring pain during general anesthesia is difficult because communication with the patient is impossible. The focus of this project is the evaluation of an objective score (‘Analgoscore’ TM ) of intraoperative nociception based on mean arterial pressure (MAP) and heart rate (HR). The Analgoscore is used for closed-loop application of remifentanil. Methods . The Analgoscore ranges from -9 (too profound analgesia) to 9 (too superficial analgesia) in increments of 1, with -3 to +3 representing excellent pain control, -3 to -6 and 3 to 6 good pain control, and -6 to -9 and 6 to 9 insufficient pain control. According to the zone of pain, a remifentanil infusion was either closed-loopadministered (Closed-loop-group) or manually administered by the same anesthesiologist (Control group). The percentage of anesthetic time within the different control zones was recorded as well as the variability of MAP and HR and compared between the two groups. Data presented as means ± standard deviation. Results . In the closed-loop group, 16 patients (5 f, 11 m; age 49 ± 21 y) underwent anesthesia of 111 ± 44 min, and received a dose of remifentanil of 0.13 ± 0.08 μg/kg/min. During 84%, 14% and 0.5% of the total anesthesia time, the Analgoscore showed excellent, good or insufficient pain control, respectively. During 70% of the time, MAP ranged from -5% to 5%, during 21% of the time it ranged from - 10% to -5% and from 5% to 10% and during 9% of the time, it ranged from -20% to -10% and from 10% to 20% below or above the target values. Heart rate was within 10% of target value in 99% of the total anesthesia time. Artifacts were recorded only 1.5% of the time. The control group of eleven patients (4 f, 7 m; age 57 ± 16 y) underwent anesthesia of 110 (25) min; remifentanil of 0.17 (0.1) μg/kg/min was infused. Excellent control was obtained 79% of the time, whereas good control and insufficient control yielded 16% and 0%, respectively. Artifacts were recorded 5% of the time. Discussion . The Analgoscore is a novel score of intraoperative nociception based on blood pressure and heart rate. Remifentanil was successfully closed-loop-administered using this score. The closed-loop system provided equal hemodynamic stability to meticulous manual administration of remifentanil.