The Effect of Decrease in Cardiac Output on End-Tidal CO2 and Difference between Arterial and End-Tidal CO2 Tension

Park, Cheol Joo

Abstract

Capnogram, monitoring of end-tidal CO2, has been a popular tool for assessment of ventilatory status during modern anesthesia. A normal curve on capnogram suggests normal CO2 production, adequate circulation, and adequate ventilation. Level of end-tidal CO2. is different from that of arterial CO2 even in normal individual. The difference is originated from alveolar dead space gas which dilute concentration of CO2 from normal alveoli. In clinical situation, the major factor which determines alveolar dead space is low pulmonary blood flow. Decrease of alveolar capillary perfusion from low cardiac output is the most important cause of low measure of end-tidal CO and large difference between arterial CO2 and end-tidal CO2 concentration in perioperative period. To understand the effect of cardiac output on end-tidal CO2 tension and the difference between arterial CO2 tension and end-tidal CO2 tension, We measured cardiac output before and dutiag administration of nitroglycerine and sodium nitropruside for relieve of myocardial load before aortic clamping in 30 male patients undergoing aortic recontructive surgery under endotracheal anesthesia for repair of infrarenal aortic obstruction. We also measured arterial CO2 tension, and end-tidal CO2 tension at the time of 10% decrease(phasel), 15% decrease(phase2)and 20% decrease(phase3) of cardiac output respectively. Measured values were statistically analyzed to evaluate correlation between cardiac output and end-tidal CO2 tension. The results are as follows: 1) Decreases of cardiac output brought about significant decrease in end-tidal CO2 in all phases compared to control value(p<0,05). 2) Decreases of cardiac output brought about significant increase in the difference between arterial- end-tidal CO2. tension in all phases compared to control value(p<0.05). 3) Changes in cardiac ourput correlated with changes in end-tidal CO2 tension significantly(p=0.0001, r=0.61, slope=2.01). 4) Changes in cardiac ourput correlated with changes in differences between arterial-end-tidal CO2 tension significantly(p=0.0001, r=-0.59, slope=-1.63). In conclusion we suggest that measurement of end-tidal CO2 tension, especially difference between arterial and end-tidal CO2 tension, may be a useful indicator for detection of cardiac output change during operation.