The Doppler CO2 test to exclude patients not in need of extracranial/intracranial bypass surgery.

In patients with an internal carotid artery (ICA) occlusion who suffer from ipsilateral transient ischaemic attacks or minor stroke extra/intracranial (EC/IC) bypass surgery may be useful only where there is insufficient collateral supply. The transcranial Doppler CO2 test offers a simple method of investigating the residual autoregulatory capacity which gives quantitative information about the efficiency of the collaterals. In 155 patients with 162 ICA occlusions there was a significant correlation between a markedly decreased or exhausted autoregulatory capacity and a recent ipsilateral ischaemic event (p less than 0.001). The Doppler CO2 test may enable the exclusion of patients not in need of EC/IC bypass surgery. In the reported series this affected more than 80% of all ICA occlusions.