M. Mijajlovic
Neurology Clinic, Clinical Center of Serbia and School of Medicine University of Belgrade – Belgrade, Serbia
Transcranial Doppler (TCD) is a relatively new, non-invasive tool, allowing for bedside monitoring to determine flow velocities indicative of changes in vascular caliber.
It has been frequently employed for the clinical evaluation of cerebral vasospasm following subarachnoid hemorrhage (SAH). To a lesser degree, TCD has also been used to evaluate cerebral autoregulatory capacity, monitor cerebral circulation during cardiopulmonary bypass and carotid endarterectomy, to diagnose brain death and for monitoring of cerebral hemodynamics in neurotrauma.
TCD is a suitable bedside method for daily assessment of the changes of intracranial pressure (ICP) by continuous monitoring of the changes of blood flow velocities and pulsatility index (PI), reflecting decreases in cerebral perfusion pressure due to increases in ICP.
Growing body of literature demonstrates the usefulness of transbulbar B-mode sonography of the optic nerve for detecting increased ICP in patients requiring neurocritical care.
TCD findings compatible with the diagnosis of brain death include systolic spikes without diastolic flow or with diastolic reversed flow, and no demonstrable flow in a patient in who flow had been clearly documented on a previous examination. Assessment of cerebral autoregulation using TCD blood flow velocity has been previously validated to be predictive of outcome following traumatic brain injury.
The commonly used bedside methods of determining the status of autoregulation include the transient hyperemic response test, the leg-cuff deflation test and reaction to spontaneous blood pressure fluctuations.
TCD PI has emerged as a surrogate marker for ICP. The measurement of PI is also an useful adjunct to guide the use of hyperosmolar therapy in various conditions with intracranial hypertension.
However, some other important, confirmed utilities of TCD in neurocritical care are overlooked, including spontaneous emboli detection, right-to-left shunt identification, early diagnosis and treatment of acute stroke, and early prognosis after recovery of cardiac arrest.
Key words: monitoring, neurocritical care, ultrasonography.