Arterial blood gases during cardiac arrest: markers of blood flow in a canine model

Measures of CO₂ have been shown to correlate with coronary perfusion pressure and cardiac output during cardiac arrest. We evaluated arterial pH (pH_a) relative to blood flow during cardiac arrest in a canine electromechanical dissociation (EMD) model of cardiac arrest using different resuscitation techniques. Following 15 min of cardiac arrest, 24 mongrel dogs received epinephrine with continued CPR or closed-chest cardiopulmonary bypass. Central arterial blood gases, end-tidal carbon dioxide (P_etCO₂), coronary perfusion pressure and cardiac output were measured. During CPR, prior to epinephrine or bypass, there was no correlation of pH_a, P_ACO₂ and P_etCO₂, with cardiac output or coronary perfusion pressure. Immediately after instituting the resuscitation techniques, both pH_a and P_aCO₂ showed a significant correlation with cardiac output (pH_a; R = -0.78, P < 0.001 and P_aCO₂; R = 0.87, P < 0.001) and with coronary perfusion pressure (pH_a; R = -0.75, P < 0.001 and P_aCO₂; R = 0.75, P < 0.001). Eventual survivors (n = 15) had an early significant decrease in pH_a, base excess and a significant increase in P_aCO₂ which was not present in non-survivors (n = 9). Neither pH_a nor P_aCO₂ correlate with blood flow under low flow conditions of CPR. However, with effective circulatory assistance, pH_a and P_aCO₂ reflect systemic blood flow and reperfusion washout.