When to Order Transcranial Doppler (TCD)
Transcranial Doppler (TCD) should be ordered in specific clinical scenarios including suspected cerebral vasospasm after subarachnoid hemorrhage, assessment of traumatic brain injury severity, detection of right-to-left cardiac shunts, monitoring for cerebral emboli, evaluation of stroke mechanisms, and assessment of intracranial stenosis.
Indications for TCD in Cerebrovascular Disease
Cerebral Vasospasm Detection
- TCD is strongly indicated for screening and monitoring of cerebral vasospasm in patients with subarachnoid hemorrhage (SAH)
- Begin monitoring on day 4 post-SAH and continue through day 10-14 1
- TCD predicts delayed cerebral ischemia with 90% sensitivity and 92% negative predictive value, though with lower specificity (71%) 1
- Vasospasm monitoring should not be extended beyond day 10 post-SAH as it does not increase detection of delayed cerebral ischemia 1
Acute Stroke Evaluation
- TCD can detect large vessel intracranial occlusions but should not delay thrombolytic therapy within the 3-hour window 1
- For patients presenting >3 hours after stroke onset, vascular imaging including TCD is strongly recommended (Class I, LOE: A) 1
- TCD can help detect microembolic signals in patients with suspected cardioembolic stroke 1
- TCD can be used to monitor recanalization during or after thrombolytic therapy 1
Traumatic Brain Injury Assessment
- TCD is suggested as an additional tool to assess traumatic brain injury severity 1
- Use TCD to estimate cerebral perfusion pressure through Pulsatility Index (PI) calculation 1
- Low mean blood flow velocity (<28 cm/s) or combination of low velocity and high PI (>1.4) is associated with higher mortality in TBI 1
- In moderate or mild TBI patients, PI value >1.25 and diastolic velocity <25 cm/s predict secondary neurological deterioration 1
Other Important Indications
Intracranial Stenosis Evaluation
- TCD can detect intracranial stenoses with sensitivity 70-90% and specificity 90-95% for anterior circulation 1
- For definitive diagnosis of stenosis degree, CTA and DSA are more accurate and should be used (Class I, LOE: A) 1
Sickle Cell Disease Monitoring
- TCD is useful for monitoring patients with sickle cell disease who might benefit from transfusion therapy 1
- Regular screening helps identify patients at high risk for stroke
Brain Death Confirmation
- TCD can be used as a supplementary test for confirmation of brain death 2
- Provides real-time assessment of cerebral circulatory arrest
Right-to-Left Shunt Detection
- TCD with bubble study can detect right-to-left cardiac shunts (e.g., patent foramen ovale) 2
- Particularly useful when evaluating cryptogenic stroke in younger patients
Limitations and Considerations
- TCD has poor sensitivity (63%) for detecting delayed cerebral ischemia after SAH, with nearly 40% of patients with DCI never attaining mean blood flow velocity >120 cm/s 3
- Technical limitations include operator dependency and inadequate acoustic windows in some patients
- TCD should not delay administration of thrombolytics in acute stroke within the treatment window 1
- TCD should be performed by trained personnel with experience in cerebrovascular ultrasound techniques
Practical Implementation
- For vasospasm monitoring: Perform TCD on days 4,7,10, and 14 after SAH 4
- For TBI assessment: Perform TCD on admission to evaluate cerebral hemodynamics 1
- For acute stroke: Consider TCD as part of the vascular evaluation, particularly beyond 3 hours from symptom onset 1
- For sickle cell disease: Follow established screening protocols based on patient age and previous TCD results
TCD remains a valuable, non-invasive bedside tool that provides real-time hemodynamic information about cerebral circulation, complementing structural imaging in various neurological conditions.