Core and thenar skin temperature variation during prolonged abdominal surgery: Comparison of two sites of active forced air warming

Background: This study was designed to compare the efficacy of two different sites of active forced air warming, upper body or lower body, to maintain normothermia; and their respective effect on thenar skin temperature in relation to the accelerographic monitoring of neuromuscular blockade during long-lasting abdominal surgery. Methods: Twenty-six patients were randomised into two groups: upper body, (n=13) and lower body, (n=13), for intraoperative forced air warming. General anaesthesia was induced with thiopentone, sufentanil, and maintained with a mixture of N₂O/O₂/isoflurane. Pancuronium, 0.1 mg · kg^-1 was used to facilitate tracheal intubation. Reinjection doses of 0.01 mg · kg^-1 were administered once 25% recovery of first twitch height of train-of-four stimulation had occurred, or if surgical relaxation was estimated as inadequate by the surgeon. Thenar skin temperature and core temperature were monitored continuously. Results: A similar trend for core temperature profile was observed in both groups. After an initial mild hypothermia, normothermia was reached progressively. Normothermia was obtained faster with lower body forced air warming than with upper body (2 h versus 3 h), P<0.05. Thenar skin temperature significantly increased during the first 90 min of surgery. This rise was significantly higher in the upper body group at 40 min and 60 min, P=0.03 and P=0.01, respectively. Stabilisation of thenar skin temperature occurred after 2 h without any further significant difference between groups. Muscle relaxant requirements were not significantly different between the groups. Conclusion: This study suggests that during long-lasting abdominal surgery, normothermia is maintained after 2-3 h by either upper or lower body active forced air warming. After an initial post-induction mild hypothermia, normothermia was achieved faster with lower body surface warming. Thenar skin temperature trend showed that it remained above 32°C during most of the procedure in both groups.