End-tidal Pco2 (Petco2) is a quantitative indicator of pulmonary blood flow generated by precordial compression and therefore predicts resuscitability during CPR. A striking increase in Petco2 follows return of spontaneous circulation. Since Paco2 is closely related to alveolar Pco2 (Paco2) and therefore Petco2, we hypothesized that Paco2 may itself serve as an indicator of the blood flow generated during CPR.
In a porcine model of cardiac arrest, Paco2 during precordial compression was highly correlated with Petco2 (r = .89), cardiac output (r = .72), and coronary perfusion pressure (CPP) (r = .74). In 14 successfully resuscitated animals, Paco2, Petco2, and CPP during precordial compression were significantly higher than in nine nonresuscitated animals. After restoration of spontaneous circulation, there was a marked increase in Paco2 to levels exceeding control values, which corresponded to the sharp increase in Petco2 that is characteristic of successful resuscitation.
We therefore confirm that both Petco2 and Paco2 correspond to the pulmonary blood flow and therefore cardiac output which is generated by precordial compression during CPR. Moreover, both serve as prognosticators of cardiac resuscitability and early indicators that spontaneous circulation has been restored.