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

Objective: To document the relationships between cardiac index and end-tida l carbon dioxide tension (Petco(2)) during diverse low-flow states of circu latory shock. Design: Randomized, prospective, controlled studies on animal models of hem orrhagic, 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 follo wed by reinfusion of shed blood. Septic shock was induced in five pigs by i nfusion of live Escherichia coil Cardiogenic shock followed an interval of global myocardial ischemia after inducing and reversing ventricular fibrill ation in six pigs, Measurements and Main Results: potco(2) was continuously measured. Cardiac index was measured intermittently by using conventional thermodilution tech niques. Cardiac index was correlated with Petco(2) by polynomial regression and Bland-Altman analyses. Petco(2) was highly correlated with cardiac ind ex 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 s hock, and -1 +/- 12 (+/- 2 sD) ml/min/kg during cardiogenic shock. Conclusions: Cardiac output and Petco(2) were highly related in diverse exp erimental models of circulatory shock in which cardiac output was reduced b y >40% of baseline values. Therefore, measurement of Petco(2), is a noninva sive alternative far continuous assessment of cardiac output during low-flo w circulatory shock states of diverse causes.