CO₂ Rebreathing as effective technique to assess cerebrovascular reserve in a resource constrained environment

The use of premixed gases or intravenous acetazolamide to induce cerebral vasodilatation is well established, but not readily available in Low- and Middle-Income Countries.

Evaluate a low-cost, closed-circuit inhaled CO₂ method to induce cerebral vasodilatation, and thus measuring cerebrovascular reserve using CT perfusion imaging.

A retrospective review of patients who have already undergone a cerebral vascular reserve test at Tygerberg Hospital as their routine investigation and treatment. Twelve regions of interest (ROIs) were identified in a standardised layout, designed to exclude watershed areas. Non-pathological regions were designated Region Type 1, and pathological regions were designated Region Type 0. An increase in cerebral blood flow (CBF) > 10% was accepted as intact autoregulation. Statistical analysis clustered data by patient and used robust standard errors.

Nine patients were reviewed. One was excluded based on a technical error in contrast medium administration. Another was excluded as all 12 ROIs were diseased. Seven patients yielded 84 ROIs, 43 (51%) of which showed no clinical or radiological features of pathology and were thus included in the final analysis. Across all 'non-pathological' ROIs, 83.72% (95% CI: 41.5% - 99.3%; p = 0.0002) demonstrated a > 10% increase in CBF after CO₂ rebreathing. The mean percentage increase was 28.5% (95% CI: 12.3 - 45.0%) CONCLUSION: The CO₂ rebreathing technique described herein produces a physiologically normal cerebrovascular reserve response in non-pathological brain tissue, comparable to more traditional methods.