ETCO2 and Cardiac Output

Cardiac output and end-tidal carbon dioxide.

Weil MH, Bisera J, Trevino RP, Rackow EC, Crit Care Med. 1985 Nov;13(11):907-9.

In this study, 19 mini-pigs were put into v-fib and their ETCO2 and cardiac output were measured prearrest, during CPR, and at ROSC. During CPR, ETCO2 decreased 21%, Cardiac output decreased 33%. At ROSC, ETCO2 returned to baseline(after initially increasing 140%) and output returned to baseline. The authors concluded there is:

• “a high correlation between ETCO2 and cardiac output(pulmonary blood flow) during CPR.”
• “ETCO2 under conditions of constant ventilation, reflects the circulatory status of the animal during and after CPR.”
• “Reductions in ETCO2 during CPR are associated with comparable reductions in cardiac output.”
• “The extent to which resuscitation manuevers, especially precordial compression, maintain cardiac output may be more readily assessed by measurements of ETCO2 than palpation of arterial pulses.”

Bottom line for EMS: ETCO2 provides a measure of the effectiveness of CPR and cardiac output. An increase in ETCO2 during arrest often signals a return of spontaneous circulation.

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

Jin X, Weil MH, Tang W, Povoas H, Pernat A, Xie J, Bisera J. Crit Care Med. 2000 Jul;28(7):2415-9

In this study 5 pigs had hemorrhagic shock induced by bleeding, 5 pigs had septic shock induced by infusion of e-coli, 6 pigs had cardiogenic shock induced by repeated episodes of v-fib. The PetCO2 was continuously measured. The results showed “Cardiac output and PetCO2 were highly related in diverse experimental models of circulatory shock in which cardiac output was reduced by >40 % of baseline values. Therefore, measurement of PetC02 is a noninvasive alternative for continuous assessment of cardiac output during low flow circulatory shock states of diverse causes.”

Bottom Line for EMS: A drop in ETCO2 may signal a drop in blood pressure for patient’s at risk for circulatory shock.

Expired carbon dioxide: a noninvasive monitor of cardiopulmonary resuscitation.

Gudipati CV, Weil MH, Bisera J, Deshmukh HG, Rackow EC. Circulation. 1988 Jan;77(1):234-9.

The authors put pigs into v-fib and monitored their ETCO2 during CPR. They wrote: “We conclude that ETCO2 provides a competent and technically simple, noninvasive monitor that highly correlates with cardiac output under conditions of constant ventilation during experimental CPR.”

Also of interest, they found: “Striking increases in ETCO2 levels that exceed prearrest values provide unequivocal evidence that spontaneous circulation has been restored such that precordial compression need not be interrupted to assess whether there has been a return of spontaneous circulation.”

Bottom Line for EMS: Instead of stopping CPR to routinely check for pulses, watch the ETCO2. If you see a sudden rise, stop and check for pulses then.