Comparison of peripheral and core temperatures in anaesthetized hypovolaemic sheep

Objective: To compare rectal (C-R degrees), coronary band (P-CB degrees) and ear base (P-E degrees) temperatures with pulmonary arterial temperature (C-PA degrees), and to investigate the relationship between core-peripheral temperature difference ([C - P]t degrees) and cardiac output (Qt) in an acute ovine trauma model (PIL 60/9064).

Study design: Observational study.

Animals: Thirteen mixed-breed male sheep, body mass (mean +/- SD) 45.50 +/- 4.21 kg, aged approximately 1 year.

Materials and methods: Anaesthesia was induced with intravenous etomidate 0.5 mg kg(-1) and midazolam 0.5 mg kg(-1) and following endotracheal intubation maintained with halothane in a 2:1 N2O:O-2 mixture. The lungs were mechanically ventilated to maintain normocapnia. Core temperature was measured using a pulmonary arterial thermistor. Rectal temperature and peripheral temperatures at the thoracic limb coronary band and ear base were recorded using themistor probes with a multi-channel recorder. Cardiac output was measured by continuous thermodilution. Recordings were taken hourly over a 24-hour period. After baseline data collection, hypovolaemia was induced by haemorrhage from bilateral femoral fractures. The development of hypovolaemic shock was confirmed by falling Qt, central venous pressure, mean arterial pressure and urine output. Resuscitation was attempted using intravenous fluids, inotropes and vasoconstrictors. Nine sheep received lumbosacral extradural bupivacaine.

Results: The rectal temperature correlated closely with pulmonary arterial temperature in all sheep (r(c) = 0.924). There was no consistent statistically significant relationship between Qt and [C - P]t degrees.

Conclusions and clinical relevance: Rectal temperature accurately reflected core temperature in anaesthetized sheep but [C - P]t degrees was unrelated to Qt, under the conditions described in this study.