To the Editor.—The article by Kram et al1 claims that by measuring transconjunctival oxygen tension (Pcjo2) one can assess adequacy of brain perfusion during carotid endarterectomy. This conclusion is drawn without the authors having actually evaluated simultaneous brain perfusion using any currently accepted method, such as electroencephalography or monitoring of regional cerebral blood flow (rCBF) and stump pressure.
My colleagues and I2 compared Pcjo2 measurements with continuous 16-channel electroencephalograms (EEGs) and rCBF measurements using Xenon Xe 133 in 18 patients undergoing carotid endarterectomy. As in the study by Kram and coworkers, the Pcjo2 value fell in all patients following occlusion of the carotid artery. However, only five of the 18 patients had any evidence of central nervous system ischemia, as detected by electroencephalography. The degree of Pcjo2 change did not bear any correlation with rCBF or identify those patients whose rCBF fell below