Transcranial Doppler determination of cerebral perfusion in patients undergoing CPR: methodology and preliminary findings. STUDY OBJECTIVES: To correlate cerebral arterial blood velocity measurements as determined by transcranial Doppler ultrasound with various resuscitation maneuvers performed in an uncontrolled manner in a series of cardiac arrest patients undergoing standard resuscitation. TYPE OF PARTICIPANTS: Any patient undergoing resuscitation for a nontraumatic cardiac arrest was eligible for the study. INTERVENTIONS: Resuscitation was carried out while flow velocities were monitored in various intracranial arteries by transcranial Doppler ultrasound. Vessel identification was based on the angle and depth of insonation. MEASUREMENTS AND MAIN RESULTS: The internal carotid artery was located more consistently than either middle cerebral or ophthalmic arteries and provided superior waveforms for analysis. Alterations in flow velocity were noted and correlated to various therapeutic interventions. Flow velocities were 70% of normal during the early phase of resuscitation but deteriorated over time until there was no evidence of net forward flow. Even early in CPR, flow was demonstrated only during systole. CONCLUSION: Transcranial Doppler ultrasound appears to be a potentially promising means of determining cerebral flow in patients undergoing CPR. 