The inhibition of thermoregulatory control by anaesthesia is manifested by reduced vasoconstriction and shivering thresholds. As intraoperative bleeding can result in haemodynamic changes, including vasoconstriction, we investigated the effect of experimental bleeding on the shivering threshold in rabbits.

Twenty-four rabbits were randomly assigned to one of three treatment strategies: (1) no blood removal (control), (2) 5 mL kg−1 isovolaemic blood removal and (3) 10 mL kg−1 isovolaemic blood removal. After tracheal intubation under isoflurane anaesthesia, anaesthesia was maintained with 50% nitrous oxide in oxygen. The removed blood volume was replaced with the same volume of warm hydroxyethyl starch colloid solution. Oesophageal temperature was measured as a core temperature at 1-min intervals. After blood removal, the animal’s body was cooled at a rate of 2–3°C h−1 by perfusing water at 10°C through a U-shaped thermode positioned in the colon. Hypothermic shivering was evaluated by visual inspection, and the core temperature at which shivering was triggered was identified as the thermoregulatory threshold for this response.

Just before the cooling, the body temperature of the animals was around 38.6°C in all of the three groups. The shivering threshold in the control group was 37.2 ± 0.2°C (mean ± SD). The shivering thresholds in the 5 mL kg−1 (36.9° ± 0.3°C) and 10 mL kg−1 (36.5° ± 0.5°C) blood removal groups were significantly lower and in proportion with the volume of blood removed than that in the control group.

Isovolaemic haemodilution decreased the shivering threshold in rabbits in proportion with the volume of blood removed.

Post-anaesthetic shivering is one of the most common complications, occurring in 5–65% of patients recovering from general anaesthesia and 33% of patients receiving epidural anaesthesia. Our objective was to investigate the efficacy of intraoperative dexmedetomidine infusion on postoperative shivering.

Ninety female patients, ASA I-II, 35–60 yr old, scheduled for elective total abdominal hysterectomy with or without bilateral salpingo-oophorectomy were randomized into two groups. After endotracheal intubation one group received normal saline infusion and the other received dexmedetomidine as a loading dose of 1 μg kg−1 for 10 min followed by a maintenance infusion of 0.4 μg kg−1 h−1. In the recovery room, pain was assessed using a 100 mm visual analogue scale and those patients who had a pain score of more than 40 mm were administered 1 mg kg−1 intramuscular diclofenac sodium. Patients with shivering grades more than 2 were administered 25 mg intravenous meperidine. Patients were protected with passive insulation covers.

Post-anaesthetic shivering was observed in 21 patients in the saline group and in seven patients in the dexmedetomidine group (P = 0.001). Shivering occurred more often in the saline group. The Ramsay Sedation Scores were higher in the dexmedetomidine group during the first postoperative hour. Pain scores were higher in the saline group for 30 min after the operation. The need for intraoperative atropine was higher in the dexmedetomidine group. Intraoperative fentanyl use was higher in the saline group. Perioperative tympanic temperatures were not different between the groups whereas postoperative measurements were lower in the dexmedetomidine group (P < 0.05).

Intraoperative dexmedetomidine infusion may be effective in the prevention of post-anaesthetic shivering.