Atropine prevents midazolam-induced core hypothermia in elderly patients

Abstract

Study Objective: To test the hypothesis that core temperature is well preserved when atropine and midazolam are combined. Design: Randomized, blinded study. Setting: Department of Anesthesia, Yamanashi Medical University. Patients: 40 elderly, ASA physical status I and II patients (aged more than 60 years). Interventions: Patients were randomly assigned (n = 10 per group) to premedication with: 1) saline control; 2) midazolam 0.05 mg/kg; 3) atropine 0.01 mg/kg; and 4) midazolam 0.05 mg/kg combined with atropine 0.01 mg/kg. All premedication was given on the ward at approximately 8:30 am, ≈30 minutes before induction of anesthesia. Measurements and Main Results: Core temperatures were measured at the right tympanic membrane. Mean skin temperature was calculated as 0.3 × (T chest + T arm) + 0.2 × (T thigh + T calf). Fingertip perfusion was evaluated using forearm minus fingertip and calf minus toe, skin-surface temperature gradients. Temperatures were evaluated at the time of premedication and 30 minutes later, just before induction of anesthesia. Core temperature remained nearly constant in the control patients (0.1 ± 0.2°C; mean ± SD), whereas it decreased significantly in the patients given midazolam alone (–0.3 ± 0.1°C). Atropine alone increased core temperature (0.3 ± 0.2°C), although the increase was not statistically significant. The combination of midazolam and atropine attenuated the hypothermia induced by midazolam alone (0.0 ± 0.2°C). Initial skin-temperature gradients exceeded 0°C in all groups, indicating that the patients were vasoconstricted. The gradients were unchanged by premedication with saline or atropine. Midazolam significantly decreased the gradient (–1.8 ± 1.1°C), as did the combination of midazolam and atropine (–1.4 ± 0.9°C). Conclusions: The thermoregulatory effects of benzodiazepine receptor agonist and cholinergic inhibitors oppose each other, and the combination leaves core temperature unchanged.