What is Vasospasm?
Cerebral Vasospasm is one of the major complications after Subarachnoid Hemorrhage (SAH) as a result of an aneurysm rupture or head injury. The outcome of vasospasm is the reduction of the arterial cross-sectional area due to extended arterial vasoconstriction or external mechanical forces.
Significant arterial narrowing resulting from SAH may take around a week to develop and present detrimental clinical conditions. Early detection of vasospasm is critical since it allows timely intervention. TCD is rather specific for this condition since it allows simple, non-invasive, and continuous bedside monitoring of vasospasm development.
How to use TCD for Vasospasm and SAH
Vasospasm results in a decrease of the arterial lumen. As long as the cerebral blood flow volume does not decrease significantly, the decreased arterial cross-sectional area will cause the Doppler blood flow velocities to increase significantly. Thus, with TCD, the anterior and posterior blood flow velocities can be mapped and diagnosed for suspected vasospasm.
Furthermore, since the volume blood flow is not expected to decrease until the autoregulatory capacity is exhausted, the ratio of cerebral velocities to the extracranial Internal Carotid Artery (ICA) are additional parameters for the identification of vasospasm.
Typical ratios are defined as follows:
An increase in these ratios is suggestive of cerebral vasospasm.
Using Dolphin for Vasospasm
Vasospasm is a developing pathology and usually requires day by day monitoring of blood flow velocity values. The Dolphin system has a dedicated Vasospasm Protocol that allows setting the velocity thresholds to identify the vasospasm severity immediately. Also, the Lidegaard Ratio, Sloan Ratio, and Soustiel Ratio are automatically calculated, displayed, and printed in the examination report.
In addition, an advanced trend analysis of the cerebral velocities and pulsatility indices is provided in order to help identify the vasospasm progression and the critical time for immediate clinical intervention.
When diagnosing vasospasm, it is critical to identify the highest mean and peak blood flow velocities.
The Dolphin provides an ideal platform for that with the ability to go back in time or change depth even after the measurement is freezed to improve the detected Doppler waveform or identify higher velocities.
Furthermore, advanced offline analysis platforms allow the physicians to review the measurements in their office and scan along the time and depth axis for additional quality review and validation of the selected highest intracranial velocities.
The severity of vasospasm is generally determined as a function of the mean velocity in the vessel of interest and the ratio to the ICA mean velocity. There are several different criteria, and some options are listed here.
In the MCA, the severity of vasospasm is sometimes defined as:
|MCA Mean Velocity
|120 ≤ Mean < 150
|3 ≤ LR < 4.5
|150 ≤ Mean < 200
|4.5 ≤ LR < 6
|Mean ≥ 200
|LR ≥ 6
Vasospasm in the PCA is considered if the Mean Velocity > 85 cm/s
Vasospasm in the ACA is considered if the Mean Velocity > 80 cm/s and the Sloan Ratio > 4.0
|Basilar Mean Velocity
|Mean > 70
|SR > 2
|Mean > 85
|SR > 2.5
|Mean > 85
|SR > 3
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