Efficacy of intraoperative heat administration by ventilation with warm humidified gases and an oesophageal warming system

We measured changes in body temperature in 12 hypothermic (mean aural temperature 34.4 (SD 1.0)°C) pigs during general anaesthesia with an open abdominal cavity and the effect of two warming systems: heating of inspired gases to 39°C (intratracheal temperature) and oesophageal warming to 39°C by a water perfused oesophageal heat exchanger. Each animal underwent both treatments and the control period in random sequence. Each condition was studied over 1 h. No additional protection against heat loss (drapes, blankets, i.v. fluids warming, etc.) was used. Anaesthesia, room temperature and relative humidity, amount and temperature of infusions and extension of exposed visceral surfaces were standardized. Mean decrease in body temperature was 1.0 (0.7)°C (P <0.005) without warming and 0.6 (0.2)°C (P <0.005) with heated inspired gases: this difference was not statistically significant. Oesophageal warming was very efficient as mean body temperature did not change significantly (-0.1 (0.2)°C; ns).