Bto And Preprocedure Ecic Bypass

Balloon test occlusion (BTO) is performed prior to vessel sacrifice to assess adequacy of collateral blood flow and cerebrovascular reserve. Claimed to be safe, reliable, and simple to perform, it has been used to evaluate a multitude of vessels, including the ICA (59), straight sinus (60), and ophthalmic artery (33). However, it has been found that test occlusion of the ICA still misses a significant number of patients with inadequate cerebrovascular reserve (61). Combination with a hypotensive challenge, whereby hypotension was induced to two-thirds of mean arterial blood pressure for 20 min or until a deficit was perceived, greatly increased the sensitivity of BTO, and the predictive value of a negative test was high (62 ) . It is also recommended that patients who have undergone artery sacrifice be monitored in an intensive care unit for 48 hr to decrease the incidence of hypotension and resultant cerebrovascular ischemia (61 ).

In cases where BTO is positive, a preprocedure extracranial-intracranial (ECIC) arterial bypass is sometimes performed to improve cerebrovascular reserve. Although a key 1985 study found no benefit in the treatment of patients with extensive cerebrovascular disease by ECIC bypass, several more recent studies have demonstrated the procedure to be more promising, finding that it increases total brain blood supply and allows for the restoration of local perfusion in hemodynamically compromised brain tissue (63). Additionally, a retrospective study found that, following ECIC bypass, signs and symptoms were improved and risk for future cerebrovascular events was reduced (64). Angiography is the established means of assessing bypass patency, but MRA (65) and multislice CTA (66) appear to be effective imaging modalities as well. This adjunct is not fail-proof, however, as in the reported case of a patient who suffered a hemodynamic stroke despite ECIC bypass prior to permanent balloon occlusion (PBO); the consequent suggestion was to consider ECIC bypass before PBO in the event of reduction of more than 50% mean blood flow velocity on BTO (67).

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