Magnesium and Ketamine Reduce Early Morphine Consumption After Open Bariatric Surgery: a Prospective Randomized Double-Blind Study.

Backgrounds: Optimal pain management in bariatric patients is crucial for early recovery. This study aims to evaluate the effects of magnesium and ketamine combination on morphine consumption after open bariatric surgery (primary outcome), as well as on postoperative pain scores and occurrence of side effects.

Method: A total of 60 patients undergoing elective open gastric bypass were randomized into 3 groups. All patients received the same general anaesthesia protocol. The magnesium and ketamine group (Mg + K) received an IV bolus of magnesium 50 mg/kg and ketamine 0.2 mg/kg followed by continuous infusion of magnesium (8 mg/kg/h) and ketamine (0.15 mg/kg/h) until extubation. The ketamine group (K) received the same bolus and infusion of ketamine, together with a bolus and continuous infusion of normal saline. The placebo group (P) received normal saline. All patients received 48 h of paracetamol 1 g IV q6h and morphine sulphate 0.1 mg/kg subcutaneous q6h PRN. Morphine consumption, VAS pain scores and occurrence of side effects were recorded for 48 h postoperatively.

Results: Patients in group (Mg + K) (2.4 ± 2.62 mg) and in group (K) (2.8 ± 2.66 mg) had significantly lower morphine consumption in the PACU compared with the patients in group (P) (4.85 ± 4.51 mg) (p = 0.045). Patients in group (Mg + K) consumed significantly less morphine the first 24 postoperative hours, with a relative reduction of 87% and 21% compared with group (K) and group (P) respectively (p = 0.028). However, this difference was not observed at 48 h. No significant difference was shown between the three groups in terms of nausea and vomiting, time to extubation or excessive sedation.

Conclusion: The association of magnesium and ketamine bolus followed by infusion in open bariatric surgery appears to be safe and decreases morphine requirements in the first 24 h compared with both ketamine alone and placebo.