Predicting postoperative pain by using preoperative pain threshold in response to electrical stimulus in women undergoing gynaecological cancer surgery - Single-arm, prospective, observational study.

Background and Aims:Individual variability leading to different pain experiences makes pain prediction challenging. This study aimed to evaluate whether preoperative electrical pain threshold testing is predictive of postoperative pain. Methods:Following ethics committee approval and registration of the trial, 40 consenting patients undergoing open laparotomy (interval debulking surgery) for ovarian cancer were included in the study. Electrical stimulus (maximum of 256 μA) was used preoperatively to determine the current perception threshold (CPT) and pain equivalent current (PEC). A numerical rating scale (NRS; 0-10, with 0 indicating no pain and 10 indicating severe pain) was used to assess pain. All patients received intravenous paracetamol in accordance to body weight, diclofenac (1 mg/kg, maximum 50 mg), and tramadol (1 mg/kg, maximum 50 mg) eight hourly for 24 hours. The preoperative PEC was compared with worst pain score (PS) at movement at the end of 24 hours. PEC was also compared with average PS at rest, at movement, and with opioid requirement (24 hours). Results:The median values of CPT and PEC were 12.51 (45 [10.1-14.6]) μA and 94.75 (174 [48.8-94.7]) μA, respectively. A moderate correlation was observed between PEC and worst PS (P = 0.01, r = -0.402), with patients having PEC less than 60 μA being associated with moderate-to-severe PS. There was no correlation between PEC and average PS at rest (P = 0.16, r = 0.225), at movement (P = 0.46, r = 0.119), and the postoperative opioid consumption in the first 24 hours (P = 0.50, r = -0.110). Conclusion:There is a moderate association between preoperative pain threshold in response to electrical stimulus and worst PS in the postoperative period following interval debulking surgery for ovarian cancer.