End-tidal carbon dioxide tension as a monitor of native blood flow during resuscitation by extracorporeal circulation

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In a porcine model of cardiac arrest, we investigated end-tidal carbon dioxide tension as a monitor of native blood flow during resuscitation by extracorporeal circulation. After 15 minutes of cardiac arrest and after precordial compression and transthoracic countershocks had failed, extracorporeal circulation consistently restored spontaneous circulation. Native end-tidal carbon dioxide tension, which averaged 29.8 +/- 1.0 mm Hg before arrest, was only 5.2 +/- 0.8 mm Hg during precordial compression. After the start of extracorporeal circulation, native end-tidal carbon dioxide tension was measured during 15-second interruptions of pump flow. End-tidal carbon dioxide tension progressively increased with a corresponding increase in native cardiac index. The correlation coefficients between end-tidal carbon dioxide tension and native cardiac index averaged 0.92 +/- 0.03 (mean +/- standard error of the mean). When end-tidal carbon dioxide tension exceeded 15 mm Hg, mean aortic pressure in each instance was 60 mm Hg or greater, and the animal was successfully weaned from extracorporeal support. We conclude that end-tidal carbon dioxide tension serves as a reliable monitor of blood flow through the lung and therefore of native cardiac output during weaning from extracorporeal circulation. It therefore indicates when native cardiac output is likely to be adequate to sustain spontaneous circulation.