Preventive analgesia: Effect of small dose of ketamine on morphine requirement after renal surgery

BACKGROUND: N-methyl D-Aspartate (NMDA) receptors seem to be responsible for pain memory and their blockade can contribute significantly in prevention of pain. This study was conducted to evaluate the preventive effect of small dose of ketamine, a NMDA receptor blocker, given before skin incision in renal surgery, with the aim to compare analgesic efficacy, intra operative and post-operative side effects. MATERIALS AND METHODS: In a prospective double-blind study, 60 American Society of Anesthesiologists (ASA) risk I and II adult patients scheduled for elective open renal surgeries by flank incision were randomly divided in two groups. Ketamine group (group K) received ketamine 0.15 mg/kg intravenously, 30 minute before start of surgery followed by infusion of ketamine 2 mcg/kg/min till start of skin closure. Control group (group C) received normal saline in place of ketamine. Both groups received morphine 0.15 mg/ kg i.v. at the time of skin closure. The analgesic efficacy was judged by visual analogue scale (VAS) at rest and on movement, time to first analgesic and morphine consumption in 24 hours. Opioid or ketamine related side effects were also recorded. RESULTS: Patients in ketamine group had significantly lower VAS score, longer time to first analgesic (21.6 ± 0.12 Vs 3.8 ± 0.7 hrs), and lower morphine consumption (5.8 ± 1.48 Vs 18.1 ± 1.6 mg) in 24 hours. There were no demonstrable side effects related to ketamine in group K whereas incidence of nausea and vomiting was higher in group C. CONCLUSION: Our results demonstrate that small dose of ketamine decreases post-operative pain, reduces morphine consumption, and delays patients request for analgesia beyond the clinical duration of action of ketamine after open renal surgery.