Continuous measurement of cerebral blood flow velocity using transcranial Doppler reveals significant moment-to-moment variability of data in healthy volunteers and in patients with subarachnoid hemorrhage

Objective: The reliability of intermittent transcranial Doppler has not been accepted widely because of problems with interobserver variability and lack of accuracy. The limitations of intermittent transcranial Doppler are thought to be overcome by continuous measurement systems. However, little published data exist on their accuracy, feasibility, and moment-to-moment variability. In this study we aimed to determine the time-related variability of continuous transcranial Doppler signal from volunteers and patients with subarachnoid hemorrhage and to examine the feasibility, ease of use, and quality of data generated from continuous transcranial Doppler for the detection of vasospasm. Design: Prospective observational study. Setting: Intensive care unit in a tertiary referral center. Subjects: Ten volunteers and eight patients with aneurysmal subarachnoid hemorrhage. Interventions: None. Measurements and Main Results: The middle cerebral artery blood flow velocities were recorded continuously from both patients and volunteers. The moment-to-moment variability of continuously recorded data was calculated. There was a wide range of velocity measurements in both volunteers and patients. There was a significant moment-to-moment variability in both volunteers (-31% to 58%) and in patients (-38% to 78%). There was a greater number of observations exceeding 10% moment-to-moment variability in the patient group with regard to systolic and diastolic velocities compared with volunteers (8% vs. 2%, p < .001). There was a trend toward a longer duration of good quality data in volunteers compared with patients (98 ± 0.5% vs. 96 ± 9%). Conclusions: Continuous measurement of cerebral blood flow velocities revealed a significant moment-to-moment variability in both patients and in volunteers, the magnitude of which was greater in the patients. The clinical implications of these findings are discussed.