End-tidal carbon dioxide as a noninvasive indicator of cardiac index during circulatory shock

Objective: To document the relationships between cardiac index and end-tidal carbon dioxide tension (Petco(2)) during diverse low-flow states of circulatory shock. Design: Randomized, prospective, controlled studies on animal models of hemorrhagic, septic, and cardiogenic shock, Setting: University-affiliate research laboratory. Subjects: Sixteen anesthetized domestic pigs weighing 35-45 kg, Interventions: Hemorrhagic shock was induced in five pips by bleeding followed by reinfusion of shed blood. Septic shock was induced in five pigs by infusion of live Escherichia coli Cardiogenic shock followed an interval of global myocardial ischemia after inducing and reversing ventricular fibrillation in six pigs, Measurements and Main Results: potco(2) was continuously measured. Cardiac index was measured intermittently by using conventional thermodilution techniques. Cardiac index was correlated with Petco(2) by polynomial regression and Bland-Altman analyses. Petco(2) was highly correlated with cardiac index during hemorrhagic shock (r(2) = .69, p < .01), septic shock (r(2) = .65, p < .01), and cardiogenic shock (r(2) = .81, p < .01), Petco(2) predicted thermodilution cardiac index with bias of -11 +/- 27 (+/- 2 sD) ml/min/kg during hemorrhagic shock, 1.3 +/- 20.4 (+/- 2 SD) ml/min/kg during septic shock, and -1 +/- 12 (+/- 2 sD) ml/min/kg during cardiogenic shock. Conclusions: Cardiac output and Petco(2) were highly related in diverse experimental models of circulatory shock in which cardiac output was reduced by >40% of baseline values. Therefore, measurement of Petco(2), is a noninvasive alternative far continuous assessment of cardiac output during low-flow circulatory shock states of diverse causes.