Incidence of perioperative hypothermia in a high-quality high-volume spay/neuter setting and association with environmental temperature

Abstract

Introduction: Perioperative inadvertent hypothermia (PIH) can prolong anesthetic recovery times. Study goals included determining PIH incidence (rectal temperature<36°C (96.8°F)) in the high-quality high-volume spay/neuter (HQHVSN) setting and evaluating associations between environmental temperature and PIH incidence. Secondary objectives included evaluating associations between PIH incidence, anesthesia recovery times, and postoperative pain. Methods: Prospective observational cohort study conducted at five HQHVSN shelters enrolling dogs undergoing ovariohysterectomy or castration and cats undergoing ovariohysterectomy. Blankets and electric heating pads were only used routinely in the immediate postoperative period. Regression models were used to evaluate associations between PIH incidence, environmental temperature, and pain data. Results: One hundred and forty dogs undergoing 65 castrations and 75 ovariohysterectomies, and 161 cats were enrolled. Mean surgical times were 19.6 (8.0) min (canine ovariohysterectomies), 7.2 (3.0) min (canine castrations), and 10.6 (3.6) min (feline ovariohysterectomies). PIH incidence was 22% (95% CI = 17–27). The risk of developing PIH was associated with environmental temperature, with a 22% increase in the odds of experiencing PIH for each degree centigrade decrease in environmental temperature (OR = 1.22, 95% CI = 1.03–1.44, P = 0.02) over a recorded range of 15.6–26.1°C (60.1–79.0°F). In cats, PIH was associated with a prolongation of time to extubation by 3.8 min (95% CI 2.27–5.37, P = 0.01). On average, each degree centigrade reduction in rectal temperature at extubation was associated with an increase in pain scale of 0.51 units (95% CI = 0.06–0.97, P = 0.03) for both species. In dogs, each degree centigrade reduction in rectal temperature at extubation was associated with a reduction in mechanical threshold (indicating increased sensitivity to pain) of 1.40 N (95% CI = 0.44–2.35, P = 0.004). Conclusion: PIH is common in a spay/neuter population despite rapid surgical times and is associated with prolonged anesthetic recovery in cats and increased postoperative pain in cats and dogs. Raising the environmental temperature in operative and recovery areas may reduce incidence.