Background: Cerebral blood flow (CBF) volume can be measured at bedside by color duplex flowmetry of the extracranial cerebral arteries. In neurointensive care patients, we prospectively tested the hypothesis that a CBF volume <100 ml/min indicates imminent cerebral circulatory arrest.
Methods: CBF volume was determined as sum of flow volumes in the internal carotid and vertebral arteries of both sides. In 192 neurointensive care patients, 829 measurements were taken. When CBF volume fell short of 100 ml/min, common carotid and external carotid artery flow volumes were also measured, and transcranial color-coded duplex sonography (TCCD) of basal cerebral arteries was performed. Results were compared with actual clinical conditions, outcome, and previously published reference data.
Results: All 41 patients with CBF volume <100 ml/min (range, 0-89 ml/min) were officially declared brain dead 2-126 hours after the measurement (median, 23 hours). TCCD revealed signs of cerebral circulatory arrest in all patients with a patent acoustic bone window. External carotid artery flow volumes were normal. The lowest CBF volume rate recorded in a surviving patient was 208 ml/min.
Conclusions: Early confirmation of cerebral circulatory arrest is of decisive importance if the patient is a potential organ donor. CBF volume measurement allows confirming the arrest of cerebral circulation even in patients without a patent acoustic bone window for TCCD. Because the critical lower threshold for survival appears to lie at 200 ml/min, bedside monitoring of CBF volume in neurointensive care patients may indicate a therapeutic window before irreversible circulatory arrest occurs.