Electroencephalographic changes during whole body hyperthermia in humans

Abstract As part of a protocol of the National Cancer Institute, 21 selected patients were submitted to total body hyperthermia for treatment of metastatic carcinoma. Elevation body temperature up to 41.8°C for 2 h was achieved using a computer driven external heating system. Patients were sedated during treatment. To ensure the safety of the procedure, a battery of physiological parameters was monitored. Continuous EEG recordings were carried out in all patients. Analysis of the EEG included visual assessment, compressed spectral array and power spectrum. EEG data were compared mainly to body temperature, state of consciousness and drug administration. Consciousness during the treatment varied from very light sedation to light anesthesia, with some rare delirious episodes. No motor seizures were observed. All EEG recordings demonstrated major changes in both rhythmicity and amplitude (slower and lower) indicating a diffuse decrease of cortical activity during the hyperthermia period. All changes reversed themselves during the cooling period. Spectral power showed a statistically significant inverse relationship with temperature. At temperatures above 41°C, decrease in total EEG spectrum was not related to decrease in clinical reactivity. The degree of EEG slowing varied with the extent and duration of the hyperthermia, and was totally reversible within a few hours of cooling, without evidence of any EEG or neurological sequelae. However, at temperatures above 41.5°C, EEG changes compatible with metabolic or toxic encephalopathy were observed. Possible mechanisms are discussed.