Evaluation of four warming procedures to minimise heat loss induced by anaesthesia and surgery in dogs

OBJECTIVE: To evaluate the efficiency of four warming procedures, introduced after anaesthetic induction and continued during surgery, in minimising heat loss in anaesthetised dogs. DESIGN: Dogs were paired. One of each pair was a control; the other was subjected to one of four warming procedures. METHODS: Ninety-six dogs were involved in total. Pairs of dogs were matched for breed, hair length, and type of surgical procedure and placed adjacent to each other in a large temperature-controlled surgical theatre. One dog within each pair was assigned to one of four warming procedures that commenced immediately after anaesthetic induction. Group 1 (11 pairs) were placed on a purpose-designed prewarmed (41 degrees C) electrically heated pad. Group 2 (18 pairs) were placed on a prewarmed electric heat pad (41 degrees C), cocooned by four wrapped water bottles (initially 41 degrees C) and subjected to radiant heat (150 watt lamp placed 50 cm away from the head of the dog). Group 3 (11 pairs) were surrounded by a forced air warming mattress (set at 43 degrees C). Group 4 (8 pairs) were connected via the anaesthetic breathing circuit to a heater/humidifier (set at 41 degrees C). Rectal temperature measurements were recorded every 15 min for the first 3 h of anaesthesia. The fall in rectal temperature of the control dog was subtracted from the fall in temperature of the treatment dog and this measurement was used to assess the efficacy of the various warming procedures. RESULTS: The mean rectal temperature of unheated 'control' dogs decreased 1.9 +/- 0.6, 1.4 +/- 0.4 and 1.1 +/- 0.4 degrees C over the first, second and third hour respectively. After 3 h the temperature fall differential for all groups were 0.7 +/- 0.7 (Group 1), 3.1 +/- 1.1 (Group 2), 2.4 +/- 1.1 (Group 3) and 1.0 +/- 1.1 degrees C (Group 4). Thus the group 2 procedure was the most successful in preventing a drop of temperature followed by groups 3, 4 and 1. CONCLUSION: Large dogs undergo significant reduction in core body temperature especially during the first 2 h of anaesthesia and surgery. Supplementary warming substantially reduces this fall in body temperature, although certain warming procedures were found to be more effective than others.