Study On The Relation Between The Preoperative Pain Sensitivity And Postoperative Analgesic Consumption

Objectve To provide a personalized PCA analgesic demand by examining the relationship between the preoperative pain threshold and tolerance and analgesic consumption.Methods One hundred and twenty patients(ASA gradeⅠ～Ⅱ,aged 40～60,no preanesthesic medicine)undergoing abdominal total hysterectomy with epidural anesthesia were divided into two groups of 60 each randomly after the operation:patient controlled intravenous analgesia(PCIA,1.0mg fentanyl and 5mg droperidol and diluted normal saline for 100ml)and patient controlled epidural analgesia(PCEA,300mg bupivacaine and 5mg droperidol and diluted normal saline for 100ml).The operation were performed by the same surgeons.An electric algometer was used preoperatively to determine the pain threshold and tolerance.A state-trait anxiety inventory(STAI)was used to assess patients' anxiety.The PCA setting:loading dose 3ml(body weight over 60kg)or 2ml(body weight less 60kg),background dose 0.1ml/h and bolus of 1ml with lock time 5 mimutes,4h limit of 30ml.A visual analog scale(VAS)was used to assess postoperative pain at rest and activity at 4h,8h,12h and 24h,and analgesic consumption,Ramsay score,vital sign and side effects were recorded at the same time.The relation between preoperative STAI score,pain threshold and tolerance and the postoperative VAS pain score and analgesic consumption was analyzed with the Pearson correlation test.Stepwise multiple regression analysis was used to determine the independent variables age,height,body weight,perioperative local analgesic consumption,duration of operation,STAI score,Ramsay score,pain threshold,pain tolerance,and that were predictive for the dependent variables analgesic consumption.Results The pain tolerance was significantly correlated with the analgesic consumption,PCIA group:r=-0.56,P＜0.01;PCEA group:r=-0.53,P＜0.01.Analgesic consumption was not significantly correlated with VAS score,STAI score,and pain threshold(P＞0.05).PCIA group:fentanyl consumption=1018.54-114.81×tolerace;PCEA group:bupivacaine consumption=297.16-33.16×tolerance.Conclusion The pain tolerance can effectively predict the PCIA and PCEA analgesic consumption.