Perioperative very low-dose ketamine infusion actually increases the incidence of postoperative remifentanil-induced shivering–double-blind randomized trial

IntroductionLow-dose ketamine infusion (blood concentration around 100 ng/mL) during surgery reduces the incidence of postoperative shivering after remifentanil-based anesthesia. We hypothesized that perioperative infusion of very low-dose ketamine (blood concentration around 40 ng/mL) during remifentanil-based anesthesia may also prevent the development of remifentanil-induced shivering during the 2-hour period after the end of anesthesia.Materials and methodsFifty female patients scheduled to undergo laparoscopic cystectomy or oophorectomy were assigned to one of two groups: (1) ketamine group, in which the patients received ketamine infusion (0.1 mg/kg/hour) from induction of anesthesia to emergence from anesthesia; and (2) control group, in which the patients received saline infusion from induction up till emergence from anesthesia. Anesthesia was induced and maintained by target-controlled infusion of propofol (estimated blood concentration: 2–4 μg/mL) and infusion of remifentanil, at 0.2–0.3 μg/kg/minute. Patients were observed for shivering from the end of anesthesia to 120 minutes after anesthesia. The time point at which the patient began to shiver was recorded and assigned to one of four time periods: at emergence, from emergence to 30 minutes after anesthesia, from 30 minutes to 60 minutes after anesthesia, and >60 minutes after anesthesia.ResultsDuring the 120-minute observation period, the number of patients who shivered was higher in the ketamine group than the in control group (18 vs. 8, ketamine group vs. control group, p = 0.01). The time period during which patients began to shiver was different between the two groups (1 patient, 4 patients, and 13 patients vs. 3 patients, 2 patients, and 3 patients at emergence, from emergence to 30 minutes, and from 30 minutes to 60 minutes after anesthesia, respectively; ketamine group vs. control group, p = 0.007).ConclusionIntraoperative infusion of very low-dose ketamine during remifentanil-based anesthesia may increase the incidence of postoperative shivering.