Deep body temperature during the warming phase of cardiopulmonary bypass

We have compared deep body temperature (DBT) measured at the forehead with the core temperatures of the nasopharynx, oesophagus and rectum during the warming phase of cardiopulmonary bypass (CPB) (moderate hypothermia of 26.7-29.6 degrees C) in 12 patients. DBT was measured transcutaneously by an insulated thermistor probe that created an area of zero thermal flow between skin and subcutaneous tissue. The core temperatures measured at different sites lagged behind the increase in arterial blood temperature during warming. The trend was most marked with rectal temperature and least with oesophageal temperature. Among all measurements, the closest linear relationship was found between forehead DBT and nasopharyngeal core temperature (0.99 x nasopharyngeal temperature (degrees C) -0.07; SEE = 0.53; r = 0.99; P < 0.0001). Forehead DBT measurement may be useful as a reliable non-invasive method of monitoring cerebral temperature during CPB.