Doppler CO2 test as an indicator of cerebral vasoreactivity and prognosis in severe intracranial hemorrhages.

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Abstract
Transcranial Doppler ultrasonography is a noninvasive, reproducible technique that allows the assessment of CO2-induced cerebral vasomotor reactivity. We investigated the effect of CO2 changes on cerebral blood flow velocity in patients with severe intracranial hemorrhage and evaluated the relation between CO2 reactivity, intracranial pressure, and outcome. Transcranial Doppler parameters, intracranial pressure, arterial blood pressure, and PaCO2 were measured simultaneously in 40 patients. To determine CO2 reactivity, the initial PaCO2 of each patient was lowered by at least 6 mm Hg by controlled hyperventilation. Relative CO2 reactivity was defined as the percent change in mean flow velocity per mm Hg PaCO2 (averaged during 20 heart cycles before and after approximately 15 minutes of increased hyperventilation). A significantly reduced relative CO2 reactivity was observed in the patient group compared with a healthy, age-matched control group. Relative CO2 reactivity was maintained significantly better in patients with moderate intracranial pressure than in patients with markedly increased intracranial pressure. An indirect correlation was found between intracranial pressure and relative CO2 reactivity (r = -0.89; p less than 0.001). Clinical outcome was significantly related to the initial relative CO2 reactivity. Whereas the patients with good recovery had shown a largely preserved reactivity (mean +/- SD, 3.4 +/- 0.7%) that did not differ significantly from the control group, there was a continuous decrease up to the patients who died (0.8 +/- 0.3%). Transcranial Doppler CO2 testing in patients with severe cerebral disease and elevated intracranial pressure provides useful information regarding hemodynamic state, prognosis, and determination of beneficial effects of specific therapy.