Background: General anesthesia influences the thermoregulatory process. The aim of this study was to compare the efficacy of low-dose prophylactic ketamine with that of placebo in preventing postoperative shivering.
Methods: A prospective randomized double-blind study involved 76 ASA I and II patients undergoing general anesthesia that was expected to last no more than 2 hours. Patients were randomly allocated to receive normal saline (Group P, n = 33) or ketamine 0.5 mg kg1 (Group K, n = 33) intravenously 20 min before completion of surgery. The anesthesia was induced with propofol 2.5-3.0 mg kg(-1) and fentanyl (2-3 microg kg(-1)), atracurium 0.5 mg kg(-1) was given to facilitate orotracheal intubation. It was maintained with propofol (510 mg kg(-1) hr(-1)), fentanyl up to (5 microg x kg1 x h1) and a mixture of nitrous oxide/oxygen (2:1). Ambient temperature was maintained at 20 degrees-22 degrees C with constant humidity. Postoperative shivering in the recovery room was evaluated according to 5 point scale of Wrench.
Results: The two groups did not differ significantly regarding patient characteristics. The number of patients shivering on arrival in the recovery room, and at 10 and 20 min after operation was significantly less in Groups K than in Group P. In group P 36% have had shivering in TO whereas in group K 6%, in T10 45% in group P whereas 18% in group K. In T20 24% in group P have had shivering compared with 6% in group K, whereas in T30 9% in group P compared with 0% in group K. The incidence of free Postanaesthetic shivering (no shivering) on arrival in the recovery room T0 was: 63.6% in group P compared with 90.9 % in group K. The postoperative hemodynamic parameters were similar in the two groups. Active warming was not required in group K but was needed in 8 cases in group P. None of patients had episodes of O2 desaturation or respiratory depression during the study period. No hallucinations, delirium, nausea, vomiting, hypertension, tachycardia, and feeling like walking in the space or nystagmus were seen in any of the patients.
Conclusion: Prophylactic low-dose ketamine was found to be effective in preventing postoperative shivering.