Atropine prevents midazolam-induced core hypothermia in elderly patients

Study Objective: To test the hypothesis that core temperature is well prese rved 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 premed ication 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 p remedication was given on the ward at approximately 8:30 AM, approximate to 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 X (T-chest + T-arm) + 0.2 X (T-thigh + T-calf). Fingertip perfusion was evaluated usin g forearm minus fingertip and calf minus toe, skin-surface temperature grad ients. Temperatures were evaluated at the time of premedication and 30 minu tes later, just before induction of anesthesia. Core temperature remained n early constant in the control patients (0.1 +/- 0.2 degreesC; mean +/- SD), whereas it decreased significantly in the patients given midazolam alone ( -0.3 +/- 0.1 degreesC). Atropine alone increased core temperature (0.3 +/- 0.2 degreesC), although the increase was not statistically significant. The combination of midazolam and atropine attenuated the hypothermia induced b y midazolam alone (0.0 +/- 0.2 degreesC). Initial skin-temperature gradient s exceeded 0 degreesC in all groups, indicating that the patients were vaso constricted. The gradients were unchanged by premedication with saline or a tropine. Midazolam significantly decreased the gradient (-1.8 +/- 1.1 C), a s did the combination of midazolam and atropine (-1.4 +/- 0.9 degreesC). Conclusions: The thermoregulatory effects of benzodiazepine receptor agonis t and cholinergic inhibitors oppose each other, and the combination leaves core temperature unchanged. 2001 by Elsevier Science Inc.