Core temperature measurement in hypovolemic resuscitation. STUDY OBJECTIVES: Accurate core temperature measurement in severely hypovolemic patients can be difficult to achieve. We used a dog model to determine both a convenient method of measuring core temperature and the relative accuracy of the multiple sites. DESIGN: Prospective laboratory (animal model) study. SETTING: Operating suites in the Animal Care Department. PARTICIPANTS: Eight adult, anesthetized greyhound dogs. INTERVENTIONS: Continuous temperature monitoring by thermistors placed in the brain, central vein, tympanic membrane, bladder, rectum, esophagus, and subcutaneous tissue. Hemorrhage to 65% initial intravascular volume and autologous transfusion of cooled blood, during which serial temperature measurements were recorded. MEASUREMENTS AND MAIN RESULTS: The readings were analyzed with Pearson's correlation coefficient. Brain temperature correlated very well with tympanic membrane temperature throughout the course (r = .869, P less than .0005). Rectum, bladder, and esophagus also correlated well with brain. Central venous temperature, however, correlated poorly with temperatures at all other sites, reflecting the marked swings in intravascular temperature caused by cold transfusion. These wide variations were damped at the other sites. The best correlation of central venous temperature was with brain and bladder, although tympanic membrane correlation was fair. CONCLUSIONS: Because intravascular hypothermia appears to be the source of the arrhythmias and hemostatic abnormalities often seen during the early resuscitation of hypovolemic patients, our results suggest bladder or tympanic membrane as the initial temperature site. After the initial resuscitation, end organ (eg, brain) temperature is the most important and is most accurately reflected by tympanic membrane temperature. 