Factors that affect dog body temperature changes during anesthesia

Abstract

OBJECTIVE: To determine factors associated with change in rectal temperature (RT) of dogs undergoing anesthesia. ANIMALS: 507 dogs. PROCEDURES: In a prospective observational study, the RT of dogs undergoing anesthesia at 5 veterinary hospitals was recorded at the time of induction of anesthesia and at the time of recovery from anesthesia (ie, at the time of extubation). Demographic data, body condition score, American Society of Anesthesiologists (ASA) physical status classification, types of procedure performed and medications administered, duration of anesthesia, and use of heat support were also recorded. Multiple regression analysis was performed to determine factors that were significantly associated with a decrease or an increase (or no change) in RT. Odds ratios were calculated for factors significantly associated with a decrease in RT. RESULTS: Among the 507 dogs undergoing anesthesia, RT decreased in 89% (median decrease, -1.2°C [-2.2°F]; range, -0.1°C to -5.7°C [-0.2°F to -10.3°F]), increased in 9% (median increase, 0.65°C [1.2°F]; range, 0.1°C to 2.1°C [3.8°F]), and did not change in 2%. Factors that significantly predicted and increased the odds of a decrease in RT included lower weight, ASA classification > 2, surgery for orthopedic or neurologic disease, MRI procedures, use of an α-adrenergic or μ-opioid receptor agonist, longer duration of anesthesia, and higher heat loss rate. Lack of μ-opioid receptor agonist use, shorter duration of anesthesia, and lower heat loss rate were significantly associated with an increase in RT. CONCLUSIONS AND CLINICAL RELEVANCE: Multiple factors that were associated with a decrease in RT in dogs undergoing anesthesia were identified. Knowledge of these factors may help identify dogs at greater risk of developing inadvertent perianesthetic hypothermia.