Measuring cerebral autoregulation in stroke patients.

Abstract

To the Editor: We have read with interest the article by Georgiadis et al in the December 2002 issue of Stroke .1 The authors have attempted to examine the integrity of cerebral autoregulation in hypothermic stroke patients. We would like to raise 2 methodological issues. Despite measuring intracranial pressure, the authors have used mean arterial pressure rather than cerebral perfusion pressure to calculate the static rate of autoregulation in their patients. In patients with disturbed autoregulation, intracranial pressure will rise in response to an increase in mean arterial pressure and cerebral perfusion pressure will therefore change less than mean arterial pressure; this phenomenon is known as “false autoregulation” and has been recently reported as occurring frequently, at least in head-injured patients.2 Using mean arterial pressure instead of cerebral perfusion pressure may therefore lead to an overestimation of the static rate of autoregulation, ie, the patient seems to have better autoregulation than she or he really does. This is even more important when large increases in mean arterial blood pressure (>20 mm Hg) are used to test autoregulation, as in this study. Such large increases may lead to …