Is there any benefit to adding intravenous ketamine to patient-controlled epidural analgesia after thoracic surgery? A randomized double-blind study†

Thoracic surgery is associated with severe acute postoperative pain, leading to pulmonary complications and hyperalgesia-induced chronic pain. Thoracic patient-controlled epidural analgesia is also considered as the gold-standard postoperative analgesia. As previously described in major digestive surgery, combination with low-dose intravenous (i.v.) ketamine could potentiate epidural analgesia and facilitate pulmonary function recovery following thoracotomy. In a randomized, double-blind trial, 60 patients scheduled to undergo thoracotomy were included. All patients received a thoracic epidural catheter placed before surgery, and standardized general anaesthesia. They were allocated to two groups to receive either an i.v. bolus of ketamine at induction, followed by a continuous infusion during surgery and the first 48 h postoperatively, or an i.v. placebo (a saline solution under the same infusion modalities). Cumulative epidural ropivacaine consumption, postoperative pain scores (patient self-rated numeric pain intensity scale), analgesic rescue consumption, residual pain, haemodynamics and respiratory recovery function were recorded from 12 h to 3 months. Data were expressed as mean +/- standard deviation or median +/- interquartile range (25-75%). The comparisons between ketamine and placebo groups were performed using chi(2) or Fisher's exact tests for frequencies, and Mann-Whitney tests for quantitative variables. Epidural ropivacaine consumption was similar between groups during the first 48 postoperative hours. Postoperative pain scores and spirometric parameters were not significantly different between groups. But the incidence of postoperative nausea was significantly increased in patients owning to the ketamine group. Finally, the incidence of residual pain was similar between groups at 1 and 3 months following thoracotomy. Adding i.v. ketamine did not potentiate epidural analgesia neither to reduce acute and chronic postoperative pain nor to improve pulmonary dysfunction following thoracic surgery. Pain scores were low in both groups, mainly because of an optimized analgesia provided by the patient-controlled epidural mode, and might explain this lack of benefit in adding i.v. ketamine.