Postanesthetic shivering affects up to 65% of patients after general anesthesia, and it can be very distressing. Various drugs have been used to treat or prevent postanesthetic shivering, but the ideal drug has not yet been found. The aim of this study was to find the minimum dose of ketamine that would show an antishivering effect.

Ninety patients scheduled for total or subtotal thyroidectomy under general anesthesia were randomly allocated to three groups: Patients received saline 3 cc (Group 1; n = 30), ketamine 0.5 mg/kg (Group 2; n = 30) or ketamine 1.0 mg/kg (Group 3; n = 30) at the end of surgery. The postanesthetic shivering was evaluated by an blind investigator who was "blinded" to the dose of ketamine. The grade of shivering was assessed using a five-point scale at 0, 10, 20 and 30 minutes after the arrival to the recovery room.

The number of patients shivering on arrival to the recovery room, and at 10 minutes after the arrival of recovery room was significantly less in Groups 2 and 3 than in Group 1 (P < 0.05). However, at 20 and 30 minutes, the number of patients was not different among the groups. There was no difference within the groups that received ketamine.

The prophylactic use of 0.5 mg/kg intravenous ketamine was effective in preventing shivering after general anesthesia.