Cerebrovascular carbon dioxide reactivity and delayed cerebral ischemia after subarachnoid hemorrhage

Objective: To determine the predictors of impaired cerebrovascular reactivity (CVR) and the value of CVR in predicting delayed cerebral ischemia (DCI) after subarachnoid hemorrhage (SAH). Design: Prospective observational study. We evaluated CVR during the following intervals: period 1, SAH days 0 to 3; period 2, SAH days 4 to 7; and period 3, SAH days 8 to 10. Normal CVR was defined as an increase in mean blood flow velocity of at least 2% per 1-mm Hg increase in PCO₂. Setting: Neurointensive care unit of the Columbia Presbyterian Medical Center. Patients: Thirty-four consecutive patients with acute SAH who underwent measurement of changes in the middle cerebral artery mean blood flow velocity after carbon dioxide challenge. Main Outcome Measure: Occurrence of DCI. Results: Delayed cerebral ischemia occurred in 10 patients (29%). Impaired CVR was more frequent in patients with a poor clinical grade on admission and at the time of examination. During period 1, there was only a trend toward lower CVR in patients who later developed DCI (1.1% vs 1.9% per 1-mm Hg increase in PCO₂; P=.07). However, those who developed DCI had progressively lower CVR during periods 2 (0.7%/mm Hg vs 2.1%/mm Hg; P>.001) and 3 (0.6%/mm Hg vs 2.4%/ mm Hg; P>.001). Independent predictors of DCI included a decrease in CVR between periods 1 and 2 (P=.03) and a poor Hunt-Hess score (P=.04). Impaired CVR at any point had a sensitivity for subsequent DCI of 91% and a specificity of 49%. Conclusions: Impaired CVR in response to carbon dioxide challenge is frequent after SAH, particularly in patients with a poor clinical grade. Progressive loss of normal CVR identifies patients at high risk for DCI, and persistently normal reactivity implies a low risk.