Hypothermia in a surgical intensive care unit

Background and goal

Inadvertent hypothermia is not uncommon in the immediate postoperative period and it is associated with impairment and abnormalities in various organs and systems that can lead to adverse outcomes. The aim of this study was to estimate the incidence, predictive factors and outcome of core hypothermia at admission to a surgical ICU.

Materials and methods

All 185 adult patients who underwent scheduled or emergency noncardiac surgery admitted to a surgical ICU between April and July 2004. The tympanic membrane core temperature (Tc) was measured on arrival on the ICU and every 2 hours until 6 hours after admission. The following variables were also recorded: age, sex, body weight and height, preoperative body temperature, ASA physical status, emergency or scheduled surgery, magnitude of surgical procedure, anesthesia technique, amount of fluids during anesthesia, use of temperature monitoring and warming techniques, duration of the anesthesia, length of stay in the ICU and in the hospital, and SAPS II score. The incidence of core hypothermia at admission to the ICU and its 95% confidence interval (CI) were calculated using the cutoff point of Tc < 35.0°C. That was used to classify patients as either hypothermic or normothermic. The two groups were compared to assess the relationship between each clinical predictor and core hypothermia using univariate analysis performed by simple binary logistic regression with an odds ratio (OR) and its 95% CI.

Results

The mean (± standard deviation) admission Tc was 34.69 ± 1.02°C. Incidence of core hypothermia on ICU admission was 57.84%. Temperature monitoring (OR 0.185, 95% CI 0.053–0.651, P = 0.009), use of warming techniques (OR 0.473, 95% CI 0.258–0.865, P = 0.015) and higher previous body temperature (OR 0.402, 95% CI 0.206–0.784, P = 0.007) were significant protective factors against core hypothermia.

Significant independent predictors of hypothermia at admission were the magnitude of surgery (OR 3.110, 95% CI 1.235–7.831, P = 0.016 for medium surgery; OR 4.679, 95% CI 2.063–10.613, P < 0.001 for major surgery), use of general anesthesia or combined epidural and general anesthesia (OR 5.963, 95% CI, 1.891–18.804, P = 0.002 for general anesthesia; OR 22.50, 95% CI 2.068–244.838, P = 0.011 for combined epidural and general anesthesia), amount of crystalloids (OR 1.435, 95% CI 1.161–1.773, P = 0.001) and total blood administration (OR 1.575, 95% CI 1.142–2.170, P = 0.006), anesthesia longer than 3 hours (OR, 1.808; 95% CI, 1.002–3.263, P = 0.049) and SAPS II scores (OR 1.028, 95% CI 1.004–1.052, P = 0.020). Twenty-nine patients (15.70%) died during their hospitalization. Hypothermia was not a risk factor for mortality, not at admission, neither at 2, 4 and 6 hours after arrival on ICU. Statistically significant independent risk factors for mortality were low body weight (OR 0.970, 95% CI 0.941–0.999, P = 0.044) and low body mass index (OR 0.895, 95% CI 0.815–0.982, P = 0.019), emergency surgery (OR 7.109, 95% CI 2.902–17.419, P < 0.001), major surgery (OR 5.500, 95% CI 1.133–26.690, P = 0.034), high SAPS II scores (OR 1.105, 95% CI 1.067–1.144, P < 0.001), longer stay in ICU (OR 8.686, 95% CI 3.646–20.692, P < 0.001 for length of stay longer than 2 days) and in the hospital (OR 1.024 per day, 95% CI 1.011–1.038, P < 0.001).

Conclusions

The incidence of patient hypothermia on arrival in intensive care is very high but is not an independent factor for mortality or for staying longer in the ICU. All efforts should be made for preventing hypothermia that should include temperature monitoring and more often use of methods of warming patients and intravascular fluids.