Prophylactic Ketamine Reduces Incidence of Postanaesthetic Shivering

Abstract

General anesthesia influences the thermoregulatory process. The aim of this study was to compare the efficacy of low-dose prophylactic ketamine with that ofplacebo in preventing postoperative shivering. 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. Patientswere randomly allocated to receive normal saline (Group P, n=33) or ketamine 0.5 mg kg (Group K, n=33) intravenously 20 min before completion of surgery. The anesthesia was induced with propofol 2.5-3.0 mgkg and fentanyl (2 -3 μgkg ), atracurium 0.5 mgkg ) was given to facilitateorotracheal intubation. It was maintained with propofol (510 mgkg hr ), fentanylup to (5 μg · kg · h and a mixture of nitrous oxide/oxygen (2:1). Ambient temperature was maintained at 20°22°C with constant humidity. Postoperative shivering in the recovery room was evaluated according to 5 point scale ofWrench. The two groups did not differ significantly regarding patient characteristics. The number of patients shivering onarrival in the recovery room, and at 10 and 20 min after operationwas significantly less in Groups K than in Group P. In group P 36% have had shivering in T0 whereas in group K 6%, in T10 45% in group P whereas 18% in group K. In T 20 24% in group Phave had shivering compared with6%in group K, whereas in T309%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 O 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. Prophylactic low-dose ketamine was found to be effectivein preventing postoperative shivering.