We tested the hypothesis that premedication with i.m. midazolam decreases core temperature dose-dependently. We studied six male volunteers, in random order, on 3 days: (1) no midazolam administration (control day), (2) midazolam 0.025 mg kg-1 i.m., (3) midazolam 0.075 mg kg-1 i.m. On the first day, subjects were maintained alert during a 30-min control period. On the second and third days, midazolam 0.025 or 0.075 mg kg-1 was administered i.m. Core temperatures were measured at the right tympanic membrane. Four adhesive skin surface probes were fixed on the chest, upper right arm, lateral calf and thigh. Finger tip perfusion was evaluated using forearm minus fingertip and calf minus toe, skin surface temperature gradients. Thirty minutes after midazolam i.m., the level of sedation in the volunteers was assessed. Peripheral venous blood was obtained immediately after the assessment of the level of sedation. Tympanic membrane temperatures after administration of midazolam 0.075 mg kg-1 i.m. were significantly lower than those on the control and midazolam 0.025 mg kg-1 i.m. days at 20 and 30 min. The decreases in tympanic membrane temperatures at 30 min after midazolam i.m. became larger as the volunteers were more deeply sedated. i.m. midazolam produced a concentration-dependent decrease in tympanic membrane temperature at 30 min after midazolam 0.025 and 0.075 mg kg-1 i.m. We conclude that midazolam impaired tonic thermoregulatory vasoconstriction, allowing core-to-peripheral heat redistribution in a dose-dependent manner after i.m. administration.

TM (r = 0.56, 0.63, and 0.58, respectively). Mean differences between TM and each temperature (TG, 7"re, T9_, 0.73, 0.42, 0.37, 0.35, and 0.35. Key wordsEQUIPMENT: thermometers; thermocouples; TEMPERATURE: core temperature, measurement, tympanic membrane temperature. Tm (respectivement r = 56, r = 0,63 et r = 0,58). La diffgrence moyenne respective entre TM et chaque tempgrature (TG, TTt',3, 0,73, 0,3~ Dans le m~me ordre, l'~cart type ~tait de 0,33, 0,37, 0,35 et 0,35 Core temperature perturbations are common in the perioperative period ~ and may indicate underlying problems such as malignant hyperthermia 2 and inadvertent hypothermia. 3 Furthermore, thermal disturbances are associated with numerous complications 4-9 and should be appropriately treated, t~ Consequently, core temperature monitoring is a critical aspect of anaesthesia practice. There are various sites for core temperature measurement such as rectal, bladder, oesophageal, and tympanic membrane. ~2 The tympanic membrane shares the same CAN J ANAESTH 1996 / 43:12 /pp 1224-8

Comparison oesophageal with "deep" of distal temperature and tracheal temperaturesPurpose: ~ compare distal oesophageal (reference) temperature with "deep-sternal," "deep-forehead," and tracheal temperatures, establishing the accuracy and precision of each. Methods: We studied 20 patients undergoing general anaesthesia for gynaecological surgery. Their lungs were mechanically ventilated with a circle systgm, at a fresh-gas flow rate of 6 L-min -~ Respiratory gases were not warmed or humidified. Tracheal temperatures were recorded from a Trachelon e tube inserted =21 cm. Deepbody temperatures were measured at the sternum and forehead Using a Coretemp | thermometer. The principle of the method is to null thermal flux through a cutaneous dgk, thus obliterating thermal gradients between the sides of the disk, skin surface, and subcutaneous tissues. Distal oesophageal temperatures were measured from thermocouples incorporated into oesophageai stethoscopes. Tracheal and deep-tissue temperatures were compared with oesophageal temperature using regression and Bland and Altman analyses. Results: Tracheal, sternal, and forehead temper:atums correlated similarly with distal oesophageal temperature, correlation coefficients (r 2) being 0.7 in each case. The offset (oesophageal temperature minus study site) was considerably larger for tracheal temperature (0.7~ than for the other sites (0.2~ However, the precision was only 0.3~ at each site. Conclusion: Our data suggest that tracheal temperatures may not be an adequate substitute for conventional core-temperature monitoring sites, In contrast, the accuracy and precision of deep-tissue temperature monitoring at the sternum and forehead was sufficient for clinical use.Objectif : Comparer la temperature oesophagienne distale (rEfErence) avec la temperature sternale profonde, frontale profonde et trachEale, darts le but de verifier !'exactitude et la precision de chacune des m&hodes. M&hodes : Vingt patientes subissant un i'nteruention gyn&ologique ont EtE EtudiEes. Elles &aient ventilEes m&aniquement ~ I'aide d'un circuit circulaire, av, ec un debit de'gaz frais de 6 L.min-'. Les gaz respiratoires n'&aient e ni r&hauff& r,i humidifies. La temp&ature trach~ale &ait enregistr& sur un tube Trachelon insErE ~ =21 cm. Les temperatures corporelles profondes Etaient mesure'es au sternum et sur le front avec un thermomEtre Coretemp e. Le principe de la m&hode est d'annuler le flux thermique ~ travers un disque cutanE, et d'oblitErer ainsi les gradients thermiques ertre les c6t& du disque, la surface cutanEe et le tissu sous

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