Oxygen extraction ratio during deep hypothermic circulatory arrest (DHCA)

O₂ extraction ratio measured across the cerebral circulation during DHCA with RCP in adult patients at a temperature that produced electrocortical silence on the EEG. The O₂ extraction ratio increased over time to a maximum value of 0.6 between 30 and 40 minutes of DHCA with RCP. Simultaneously, the brainstem somatosensory evoked potential (N18) decreased in amplitude over time and disappeared approximately 30 to 40 minutes after the onset of circulatory arrest. Markers of cerebral ischemia, neuron-specific enolase, and astrocyte S-100 measured in the retrograde cerebral perfusate increased significantly at 21 to 30 minutes after the onset of circulatory arrest (not shown).