Correlation of end-tidal CO₂ to cerebral perfusion during CPR

Study objective: A number of studies have demonstrated a correlation between end-tidal carbon dioxide (ETco₂), cardiac output, and return of spontaneous circulation in experimental animals and in patients undergoing closed-chest CPR. Our study attempted to correlate ETco₂ to cerebral blood flow during cardiac arrest. Design: Sixteen piglets were anesthetized, intubated, and instrumented for cerebral blood flow studies. An ultrasonic flow probe was placed on both internal carotid arteries for continuous flow measurements. The animal was fibrillated, and closed-chest CPR was begun. Continuous ETc0₂ measurements were obtained and compared with simultaneous internal carotid, cardiac output, and cerebral blood flow measurements. Measurements and main results: Correlations between ETco₂ and carotid and cerebral blood flow were determined using Pearson's method. The correlation between ETco₂ and total internal carotid flow was .58 (P = .01, Bonferroni's adjusted P = .30). Correlation between ETco₂ and cerebral blood flow was .64 (P = .01, Bonferroni's adjusted P = .09). A partial correlation coefficient for ETco₂ versus cardiac output was .70, whereas it was only .30 for ETco₂ versus cerebral blood flow. Conclusion: Partial correlation coefficients suggest that ETco₂ correlates with cerebral blood flow when changes in cerebral blood flow parallel changes in cardiac output.