Does adding ketamine to morphine in a patient-controlled intravenous analgesia pump after orthopedic surgeries help better management of postoperative pain in obese patients? A double-blinded clinical trial

Introduction: Low doses of ketamine can cause an antagonistic effect on NMDA-receptors by blocking the magnesium-gated channels. Several studies demonstrated the effect of ketamine in improving the analgesia using opioids, however, obese people reported different reactions to this problem. Objectives: This study seeks to answer the following question: Does adding ketamine to morphine in a patient-controlled intravenous analgesia pump (PCIA) after orthopedic surgeries help better management of postoperative pain in obese patients? Patient and Methods: This double-blinded clinical trial involved 60 obese (body mass of higher than 30 kg/m²) lower limb orthopedic surgery candidates at Shohada hospital (Tabriz, Iran). The participants were randomly categorized into three groups. In group M, 20 mg morphine sulfate, in group MK1 100 mg ketamine + 20 mg morphine sulfate, and in group MK2 200 mg ketamine+10 mg morphine sulfate was added to the analgesia pump. Pain intensity (VAS), sedation score (Ramsay Scale), as well as nausea and vomiting (N&V score) were compared among different groups at 12, 24, 36, and 48 hours after the operation. Results: Group M manifested a significantly higher pain intensity than two other groups during all examined times, and group MK2 demonstrated a significantly lower pain intensity than other groups. In the course of the research, the amount of opioid consumption in group MK2 was significantly lower than in the other groups. Conclusion: The addition of a low dose of ketamine to morphine in the PCIA pump after orthopedic surgeries in obese patients results in proper postoperative pain management. Trial Registration: The trial protocol was approved in the Iranian registry of clinical trial (identifier: IRCT2017101636822N1, https://www. irct.ir/trial/27429, ethical code; IR.TBZMED.REC.1400.820).