BACKGROUND: It is well known that body core temperature reduces during general anesthesia. Midazolam premedication for relieving anxiety might also reduce body core temperature by inhibiting tonic thermoregulatory vasoconstriction in elderly patients. Therefore, an effort to maintain temperature must be started before anesthesia. This study was designed to evaluate the effect on body core temperature of midazolam, atropine and glycopyrrolate, which are commonly used for premedication.

METHODS: Six hundred and eleven patients of ASA physical status 1 or 2, aged 18 to 65, were involved in this study. They were randomly assigned to premedication with: 1) saline control (n = 92); 2) midazolam 0.04 mg/kg (n = 96); 3) midazolam 0.04 mg/kg with glycopyrrolate 0.004 mg/kg (n = 117); 4) midazolam 0.04 mg/kg with atropine 0.01 mg/kg (n = 93); 5) glycopyrrolate 0.004 mg/kg (n = 116); and 6) atropine 0.01 mg/kg (n = 97). All premedication was given intramuscularly about 30 min before operation. Temperatures were measured at the tympanic membrane at the time of premedication and 30 min after premedication.

RESULTS: Temperatures increased slightly after injection in the control (0.14 ± 0.36℃; mean ± SD) and this increase was less in the midazolam group (0.07 ± 0.39℃). The changes of temperature in the midazolam with glycopyrrolate (0.16 ± 0.39℃), midazolam with atropine (0.19 ± 0.40℃), and in the glycopyrrolate group were no different from that of the control group. However, there was a statistically significant increase in temperature after injection in the atropine group (0.26 ± 0.42℃) versus the control group. Compared with the midazolam group, a statistically significant increase in temperature was observed in the midazolam with atropine, the glycopyrrolate, and in the atropine group.

CONCLUSIONS: From these results, low dose midazolam (0.04 mg/kg), midazolam with glycopyrrolate, and midazolam with atropine for premedication have little affect on temperature. Midazolam with glycopyrrolate premedication is recommended for preserving body core temperature.