Transcranial Doppler (TCD) Ultrasonography

Transcranial Doppler (TCD) ultrasonography is one of the most widely studied non-invasive techniques for estimating ICP. TCD measures cerebral blood flow velocity in the large basal arteries of the brain, primarily the middle cerebral artery (MCA). By assessing the flow velocity and pulsatility index (PI) of these arteries, clinicians can estimate changes in ICP. The relationship between ICP and the PI, a ratio of systolic and diastolic blood flow velocities, is well-established. As ICP rises, cerebral blood flow becomes more pulsatile due to the reduced cerebral perfusion pressure. Although TCD does not provide an absolute ICP value, it can reliably detect trends and suggest whether ICP is elevated. For anesthesia providers, TCD has several practical applications. It is a quick, bedside tool that can be used during surgery or in the intensive care unit to monitor cerebral blood flow dynamics in patients at risk of elevated ICP. TCD is particularly useful during procedures where brain perfusion is critical, such as carotid endarterectomy, aneurysm clipping, or craniotomy. Furthermore, TCD can provide insights into cerebral autoregulation—the brain’s ability to maintain stable blood flow despite changes in systemic blood pressure—another vital parameter for managing neurocritical patients. However, TCD is operator-dependent, and its accuracy is influenced by patient anatomy (e.g., skull thickness). It also requires continuous monitoring, which may not always be feasible in a busy operating room. Despite these limitations, TCD remains a valuable tool for real-time monitoring of ICP-related changes.