Stages and thresholds of hemodynamic failure.

Abstract

To the Editor: Derdeyn et al1 revisited their prospective study2 on oxygen extraction fraction (OEF) by positron-emission tomography to predict stroke in patients with unilateral carotid occlusion. In it, they report for the first time that high OEF predicted increased stroke risk but only when combined with high cerebral blood volume (CBV). High OEF with normal CBV did not predict increased risk for stroke. This observation is germane to the utility of cerebrovascular reserve (CVR) for the prediction of stroke risk. But first, we will comment on the stages of hemodynamic failure and the thresholds they chose to use in the prediction of stroke by OEF. For the stages of hemodynamic failure, Derdeyn et al1 chose to depict only stages I and II without stage III. Yet, it is well recognized that there is a stage III, as depicted by Powers3 in his classic article on the relationship of the changes in cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO2), OEF, and CBV …