Transcranial Doppler Ultrasound in Subarachnoid Hemorrhage
Lindegaard ratio for middle cerebral artery vasospasm
| MFV cm/s | Lindegaard ratio | Interpretation |
| <120 | <=3 | Hyperemia |
| >80 | 3-4 | Hyperemia+possible mild vasospasm |
| >=120 | 3-4 | Mild vasospasm+hyperemia |
| >=120 | 4-5 | Moderate vasospasm+hyperemia |
| >120 | 5-6 | Moderate vasospasm |
| >=180 | 6 | Moderate-to-severe vasospasm |
| >=200 | >=6 | Severe vasospasm |
| >200 | 4-6 | Moderate vasospasm+hyperemia |
| >200 | 3-4 | Hyperemia+mild/residual vasospasm |
| >200 | 3 | Hyperemia |
Lindegaard ratio=MCA MFV/EC ICA MFV (MCA=middle cerebral artery. EC ICA=extracranial internal carotid artery. MFV=mean flow velocity.) MFV=(PSV+EDV+EDV)/3
Sviri ratio for basilar artery vasospasm
| MFV cm/s | Sviri ratio | Interpretation |
| >70 | >2 | Vasospasm |
| >85 | >2.5 | Moderate or severe vasospasm |
| >85 | >3 | Severe vasospasm |
Sviri ratio=BA MFV/EC VA MFV (BA=basilar artery. EC VA=extracranial vertebral artery. MFV=mean flow velocity.)
Vasospasm criteria for other vessels
| Possible vasospasm | Probable vasospasm | Definite vasospasm | |
| Artery | MFV cm/s | MFV cm/s | MFV cm/s |
| ICA | >80 | >110 | >130 |
| ACA | >90 | >110 | >120 |
| PCA | >60 | >80 | >90 |
| VA | >60 | >80 | >90 |
MFV=mean flow velocity. ICA=internal carotid artery. ACA=anterior cranial artery. PCA=posterior cranial artery. VA=vertebral artery.
In the presence of ipsilateral middle cerebral artery or internal carotid
artery vasospasm, the Sloan hemispheric ratio (anterior cerebral artery/
extracranial internal carotid artery >4) is used for diagnosis of ACA vasospasm instead.
Pulsatility Index (PI) increase and cerebral circulatory arrest: A focal increase in PI, indicative of a focal increase in intracranial pressure (mass effect), is valuable in guiding follow-up CT scans and at times can lead to successful hematoma evacuation. This factor is especially true for patients in whom neurologic examination is poor and cannot guide management. It is also useful in capturing reverberating or oscillating waveforms and systolic spikes that are indicative of impending or definite cerebral circulatory arrest, allowing physicians to either escalate care or initiate a brain death evaluation.