Abstract
We studied the relationship of cerebral blood flow (CBF) and cerebral O2 uptake (CMRO2) to somatosensory evoked potential (SEP) and brainstem auditory evoked response (BAER) under conditions of elevated intracranial pressure (ICP). Sheep were anesthetized with pentobarbital and pancuronium and ventilated. ICP was increased to a fixed level by infusing mock CSF into the lateral ventricle. ICP was raised to a calculated cerebral perfusion pressure of either 0, 20-25, or 50 mmHg. CBF was measured using the radiolabelled microsphere technique. CMRO2 was calculated with sagittal sinus blood samples. When CBF fell, cerebral O2 extraction increased. However, with CBF below 70% of baseline, CMRO2 was not sustained by increased extraction. BAER interwave I to V latency increased below a mid-brain blood flow of 15 ml·min−1. 100g−1. SEP central conduction time (CCT) determined from the latency differences between N1 of foreleg SEP and C2 increased below a CBF threshold of 15-20 ml·min−1·100g−1 (50-65% reduction from baseline CBF). Changes in CCT were associated with a 25% decrease in CMRO2 from baseline. Therefore, under conditions of elevated ICP, cerebral ischemia as defined by CMRO2 appears to correlate with changes in evoked potential responses. The large threshold observed when evoked potentials are related to regional CBF is probably a function of the O2 extraction reserve.
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Backofen, J., Koehler, R., McPherson, R. et al. 164 EFFECT OF ELEVATED INTRACRANIAL PRESSURE ON CERE BRAL BLOO D FLOW AND EVOKED POTENTIAL RESPONSES. Pediatr Res 19, 138 (1985). https://doi.org/10.1203/00006450-198504000-00194
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DOI: https://doi.org/10.1203/00006450-198504000-00194