DO CHANGES IN END-TIDAL PCO(2) QUANTITATIVELY REFLECT CHANGES IN CARDIAC-OUTPUT

In anesthetized patients, acute decreases in cardiac output (CO) are often reflected as decreases in end-tidal CO2 tension (PETCO(2)), but the quantitative relationship between the changes in CO and the changes in PETCO(2) is uncertain. We hypothesize that a quantitative relationship can be demonstrated if timing of the measurements in each episode of hemodynamic perturbation is standardized. In 24 patients undergoing abdominal aortic aneurysm surgery with constant ventilation, we prospectively performed 33 measurements of CO, PETCO(2), and CO2 elimination (VECO(2)) within 10 min of hemodynamic changes. The percent decrease in PETCO(2) directly correlated with the percent decrease in CO (slope = 0.33, r(2) = 0.82). Also, the percent decrease in VECO(2) correlated with the percent decrease in CO similarly (slope = 0.28, r(2) = 0.84). The changes in PETCO(2) and VECO(2) following hemodynamic perturbation were parallel. This finding suggests that decreases in PETCO(2) quantitatively reflect the decreases in CO2 elimination.