Effects of acute hypoxemia/ischemia on EEG and evoked responses at normothermia and hypothermia in humans.
BACKGROUND
Hypothermia is used clinically to prevent neurologic injury but the degree of protection which it affords at various levels of the nervous system in humans is difficult to establish.


METHODS
The temporal changes in EEG amplitude and somatosensory evoked potential (SEP) amplitudes in a patient experiencing acute normothermic hypoxemia, a patient experiencing acute circulatory arrest at moderate hypothermia and a collection of patients undergoing deep hypothermic circulatory arrest were analyzed to determine the rate at which changes occur during acute lack of oxygen delivery at various temperatures.


RESULTS
In each case, it was found that more rostrally generated potentials disappeared more quickly than more peripheral potentials. All potentials decayed more slowly during acute normothermic hypoxemia than during circulatory arrest. During circulatory arrest at 14.4 degrees C, the amplitude of the Erb's point, N13 and N18 potentials in the SEP took 5 times longer to drop to 50% of their value at the onset of ischemia than with circulatory arrest at 30.9 degrees C.


CONCLUSIONS
The longer times to disappearance of the SEP potentials during deep hypothermia compared to moderate hypothermia was consistent with the predicted 3.5-6.5 fold reduction in metabolic activity at deep hypothermia compared to moderate hypothermia. The prolonged time to disappearance of the SEP during normothermic hypoxemia demonstrates that even with reduced oxygen delivery the continued delivery of metabolic substrate can be critical to neural function.
Stecker
Mark M
MM
Department of Neurology, Hospital of the University of Pensylvania, Philadelphia, PA, USA. mmstecker@geisinger.edu
Escherich
Alison
A
Patterson
Terry
T
Bavaria
Joseph E
JE
Cheung
Albert T
AT
D000328:Adult; D001014:Aortic Aneurysm / Q000601:surgery; D001831:Body Temperature; D001925:Brain Damage, Chronic / Q000209:etiology; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory; D015199:Extracorporeal Membrane Oxygenation; D005260:Female; D006323:Heart Arrest / Q000209:etiology; D006801:Humans; D007036:Hypothermia, Induced; D020925:Hypoxia-Ischemia, Brain / Q000503:physiopathology* / Q000628:therapy; D007430:Intraoperative Care; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000209:etiology; D011655:Pulmonary Embolism / Q000601:surgery; D012640:Seizures / Q000209:etiology