Predictor of core hypothermia and the surgical intensive care unit

Abstract

Inadvertent postoperative core hypothermia is associated with multiple physiological effects, especially in patients admitted to the intensive care unit (ICU). Despite previous reports of the relationship between patient, surgical, and anesthetic factors and immediate postoperative core hypothermia, this information might need to be reconsidered in the light of progress in surgery, anesthetic, and warming techniques. We designed this prospective study of 194 postgeneral surgical patients to assess the incidence, predictive factors, and outcome of core hypothermia (tympanic membrane core temperature [Tc] <36.0 degrees C) at the time of admission to the general ICU in a large tertiary university medical center from December 2000 to March 2001. The following variables were studied: age, sex, body weight, body surface area, preoperative body temperature, ASA physical status, history of diabetic neuropathy, emergency surgery, surgical subspecialty performing surgery, type of surgery, type of anesthesia (general, regional, or combined epidural and general), temperature monitoring, use of a forced air warming technique, amount of fluid and blood replacement, duration of anesthesia, duration of surgery, and the ambient operating room temperature. Other outcomes, i.e., length of ICU stay and mortality, were also assessed. The incidence of core hypothermia was 57.1%, 41.3%, and 28.3% according to the definition of Tc <36.0 degrees C, <35.5 degrees C, and <35.0 degrees C, respectively. Multiple logistic regression showed the following risk factors for core hypothermia: high ASA physical status (odds ratio, 2.87; 95% confidence interval [CI], 0.82-10.03 for ASA II; odds ratio, 8.35; 95% CI, 1.67-41.88 for ASA >II), magnitude of surgical procedure (odds ratio, 6.60; 95% CI, 1.66-26.19 for medium surgery; odds ratio, 22.23; 95% CI, 5.41-91.36 for major surgery), use of combined epidural and general anesthesia (odds ratio, 3.39; 95% CI, 1.05-10.88), and duration of surgery >2 h (odds ratio, 4.50; 95% CI, 1.48-13.68). Not using temperature monitoring seems to be a risk factor as well (odds ratio, 3.00; 95% CI, 0.87-10.12). Significant protective factors against core hypothermia were heavier body weight (odds ratio, 0.94; 95% CI, 0.89-0.98), higher preoperative body temperature (odds ratio, 0.31; 95% CI, 0.15-0.65), and warmer ambient operating room temperature (odds ratio, 0.67; 95% CI, 0.51-0.88). In conclusion, the incidence of core hypothermia (Tc <36.0 degrees C) at the time of admission to the general ICU is still frequent. To reduce the incidence, more efforts and concern should be taken to prevent core hypothermia, especially in the patient with high ASA physical status, undergoing more intensive and lengthy surgery, and using combined epidural and general anesthesia.

Implications: In an effort to decrease the frequent incidence of core hypothermia at the time of admission to the general surgical intensive care unit, this prospective study showed that high ASA physical status, the use of a combined epidural and general anesthesia, surgery lasting longer than 2 h, and extensive surgery were the important risk factors, whereas heavier body weight, higher preoperative body temperature, and warmer ambient operating room temperature were important protective factors.