Selective venous hypercarbia during human CPR: implications regarding blood flow

Thirty-five patients presenting to the emergency department in cardiopulmonary arrest had simultaneous measurement of central venous (cv) and arterial (a) blood gases during CPR with a pneumatic chest compressor and ventilator. The mean cv, arterial pH, and PCO2 values were markedly different (P less than .001). The mean pH gradient (pHa - pHcv) was .31 +/- .10 units and the mean PCO2 gradient (PcvCO2 - PaCO2) was 60.5 +/- 23.6 torr. This selective venous hypercarbia is probably due to a cardiac output that is inadequate to eliminate the CO2 produced from both residual aerobic metabolism and the buffering of anaerobically produced lactic acid. Central venous blood gases are probably a better reflection of actual tissue environment during prolonged cardiac arrest than are arterial blood gases.