Pain following Surgery: Management, Outcome, and Prediction

Abstract: Despite advances in the treatment of postoperative pain, nearly 30% of patients experience moderate to severe pain following major surgery. The present thesis includes four studies intended to evaluate important aspects of postoperative pain. In studies I and II, patient-controlled epidural analgesia (PCEA, n = 1,670), using local anesthetics and morphine, was associated with significantly lower pain ratings than intravenous patient-controlled analgesia (PCA, n = 1,026) using morphine following major surgery. Respiratory depression, sedation, confusion, hallucinations, and nightmares were more frequently observed in the PCA group, while technical difficulties leading to insufficient analgesia were more frequent in the PCEA group. In study III, morphine pharmacokinetics were studied in patients undergoing major liver resection (n = 15) in comparison with a group undergoing colon surgery (n = 15). Liver resection was associated with higher plasma concentrations of morphine indicating a decrease in morphine clearance, compared to controls. Sedation scores were higher in patients undergoing liver resection than in controls. In study IV, the predictive potential of psychometric variables and preoperative responses to experimental heat stimuli were evaluated in patients scheduled for a laparoscopic sterilization procedure (n = 59). Pre-surgical pain and preoperative heat pain sensitivity were important predictors of postoperative pain, while psychometric estimates of vulnerability, anxiety, and depression only contributed to a lesser degree. The prediction model accounted for 29-43% of the total variance in postoperative movement-related pain. Optimum pain management requires careful consideration regarding surgical procedure, analgesic technique, pharmacokinetics, and risk factors in the development of postoperative pain.