Postoperative pain and study design: the type of surgical procedure matters
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To the Editor,
I read with interest the article of Sacevich et al. regarding the use of subcutaneous ketamine for postoperative pain in Rwanda.1 To conduct a randomized-controlled trial in a low-income country is an arduous task, and the authors should be congratulated for this effort.
Although I praise the authors for their study, there are concerns about the study design that require further clarification. The authors choose to define major surgery as “surgery requiring admission to hospital for at least two days postoperatively”. This can be extremely problematic as it can include procedures with very different pain intensities and temporal patterns (e.g., spine surgery, colectomy, craniectomy, hysterectomy). It was interesting to note that the placebo group had no patients undergoing orthopedic surgery, which is known to be very painful and often require regional anesthesia techniques. A more detailed presentation of the surgical procedures would be helpful to the reader because of the broad inclusion criteria utilized by the authors.
Additional clarification is also needed for the selection of the primary outcome. The authors selected the mean of daily pain scores on postoperative day 1 and postoperative day 2. Given the small sample size, it is likely that pain scores were not normally distributed. Lastly, the lack of standardization of non-opioid postoperative analgesics could have significantly biased the study’s results. It is unclear why the authors did not standardize non-opioid analgesics and the use of opioid analgesics for breakthrough pain, as is commonly done in acute pain studies.2, 3, 4
Conflicts of interest
This submission was handled by Dr. Philip M. Jones, Associate Editor, Canadian Journal of Anesthesia.