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

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.