Transcranial Doppler monitoring in subarachnoid hemorrhage: a critical tool in critical care

Purpose: To review the literature regarding the use of transcranial Doppler ultrasonography (TCD) for monitoring cerebral vasospasm following subarachnoid hemorrhage (SAH). Source: We searched Medline (1980 to August 2007) and Embase (1980 to August 2007) and reviewed all relevant manuscripts regarding TCD and SAH. Principal findings: Currently, the gold standard for vasospasm diagnosis is cerebral angiography, replaceable by computed tomography angiography, only when angiography is not available. Obviously, it is not feasible to perform such investigation as frequently as bedside clinical assessment. Repeated clinical assessments of a patient's neurological status carry the problem of detecting the clinical signs and symptoms of vasospasm, which occur only after vasospasm has already manifested its deleterious effects on the cerebral parenchyma. Transcranial Doppler ultrasonography is a relatively new, non-invasive tool, allowing for bedside monitoring to determine flow velocities indicative of changes in vascular calibre. Transcranial Doppler ultrasonography can be useful pre-, intra- and post-operatively, while helping to recognize the development of cerebral vasospasm before the onset of its clinical effects. Conclusion: Vasospasm following SAH is a very important source of morbidity and mortality. Too often, the first sign is a neurologic deficit, which may be too late to reverse. Transcranial Doppler ultrasonography assists in the clinical decision-making regarding further diagnostic evaluation and therapeutic interventions. When performed in isolation, the contribution of TCD to improving patient outcome has not been established. Nevertheless, TCD has become a regularly employed tool in neurocritical care and perioperative settings.