Low-dose subcutaneous ketamine for postoperative pain management in Rwanda: a dose-finding study

Good pain control is not a normal part of surgical care in sub-Saharan Africa due to lack of resources. The primary objective of this study was to determine an efficacious dose of subcutaneous ketamine for postoperative pain for use in a future randomized controlled trial.

Following research ethics board and local hospital approval for this research, we obtained informed consent from 31 patients undergoing major surgery for a random walk dose-finding study. In addition to standard postoperative care, participants received five doses of subcutaneous ketamine at scheduled intervals from arrival in the postanesthesia care unit (PACU) to postoperative day 2. Participants received 50 mg of ketamine (minimum 0.6 to maximum 1.1 mg·kg^-1, based on different body weights) for the first and second dose, with subsequent doses adjusted by 10 mg according to pain and side effects. Pain scores were recorded at rest and with movement.

The following mean (standard deviation [SD]) pain scores at rest and with movement were recorded on arrival in the PACU and on the afternoon of postoperative days 1 and 2: [at rest: 8.2 (1.5), 3.2 (1.8), and 0.7 (1.0), respectively; with movement: 9.4 (0.8), 5.1 (1.7), and 2.4 (1.1), respectively]. This rate of improvement suggests possible pain relief through use of ketamine. The mean (SD) ketamine dose that appeared efficacious in pain reduction was 0.90 (0.23) mg·kg^-1. There were no serious side effects.

Adding subcutaneous ketamine to standard analgesic measures resulted in decreases in postoperative pain scores without serious side effects. These data can be used to inform a randomized controlled trial to compare subcutaneous ketamine plus standard care with placebo plus standard care for reducing postoperative pain.