Brain temperature cannot be measured directly during deliberate hypothermia on cardiopulmonary bypass. Temperature measured within the NP or ear canal near the tympanic membrane is often used as a surrogate indicator of brain temperature. Hypothermia produces characteristic changes in the EEG that can also be used as a physiologic surrogate of the degree of suppression of cerebral metabolism. Electrocortical silence on the EEG occurs at an average NP temperature of 18°C in adults, but a NP temperature of approximately 12°C is necessary to ensure electrocortical silence in >95 percent of patients.
EEG: electroencephalogram; NP: nasopharynx.
Original figure modified for this publication. Stecker MM, Cheung AT, Pochettino A, et al. Deep hypothermic circulatory arrest: I. Effects of cooling on electroencephalogram and evoked potentials. Ann Thorac Surg 2001; 71:14. Illustration used with the permission of Elsevier Inc. All rights reserved.