Temperature monitoring during CPB in infants: does it predict efficient brain cooling?

We examined jugular venous oxygen saturation data in 17 pediatric patients less than 1 year of age undergoing hypothermic cardiopulmonary bypass (CPB). Jugular venous oxygen saturations (JvO2SATS) were measured before bypass and during the active core cooling portion of CPB. The study intervals during CPB included 1 minute after initiation of CPB, at a tympanic membrane temperature of 15 degrees C, and at a rectal temperature of 15 degrees C. During these measurement intervals, there were no significant changes in mean arterial pressure, pump flow rate, arterial oxygen saturation, mixed venous oxygen saturation, carbon dioxide tension, or hematocrit. Six of the 17 patients (29%) demonstrated a significantly lower JvO2SAT (87.1% +/- 6.3% versus 98.1% +/- 0.9%) at a tympanic membrane temperature of 15 degrees C. Patients demonstrating jugular venous desaturation could not be predicted from continuous monitoring of tympanic membrane and rectal temperatures or through on-line measurements of mixed venous oxygen saturation. Low JvO2SAT suggests higher levels of cerebral metabolism and cerebral uptake of oxygen. In the presence of deep hypothermic CPB and stable anesthetic levels, the most likely cause of a low JvO2SAT is inadequate cerebral cooling. We believe JvO2SAT monitoring may be an important adjunct to conventional temperature monitoring in the patient undergoing deep hypothermic CPB or total circulatory arrest.