The ‘Analgoscore’: a novel score to monitor intraoperative pain and its use for remifentanil closed-loop application

Abstract

Purpose: measuring pain during general anesthesia is difficult because communication with the patient is impossible. The focus of this project is the development of an objective score ('Analgoscore') of intraoperative pain based on mean arterial pressure (MAP) and heart rate (HR). The Analgoscore was used for closed-loop application of remifentanil. Methods: based on fuzzy logic algorithms, the Analgoscore ranges from -9 (too profound analgesia) to 9 (too little 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 as insufficient pain control. According to the zone of pain, a remifentanil infusion was closed-loop-administered. The percentage of anesthetic time within the different control zones was recorded as well as the variability of MAP and HR Data as means plusmn standard deviation. Results: Sixteen patients (5 f, 11 m; age 49 plusmn 21 y; weight 70 plusmn 11) underwent anesthesia of a total time of 1772 min, and received a mean dose of remifentanil of 0.13 plusmn 0.08 mug/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 targeted values. HR was within 10% of target value in 99% of the total anesthesia time. Discussion: The Analgoscore is a novel score of intraoperative pain. Remifentanil was successfully closed-loop-administered and, controlled by the Analgoscore, excellent hemodynamic stability was achieved.