An analysis of CO2 elimination curves during artificial ventilation.

We have developed some indices to evaluate the phase III slope in CO2 elimination curves. The indices were applied to 12 mechanically ventilated patients in ICU to determine their stability under various ventilator settings. Fco2-sl[30-90] and[Formula: see text] expressed the mean incline of phase III slope in Fco2-volume curves and[Formula: see text]-volume curves, respectively. Fco2-SR and[Formula: see text]-SR expressed the ratio of the slopes in the first and second halves of the phase III portion in both curves. The indices were also applied to 108 elective surgery patients to determine their usefulness in predicting ventilatory efficiency during general anesthesia. In the first study, Fco2-sl[30-90] and[Formula: see text][30-90] correlated with ETco2, Vd/Vt and the volume of CO2 expired, but Fco2-SR and[Formula: see text]-SR were independent of these parameters.[Formula: see text]-SR did not show any significant changes under various ventilator settings except for application of PEEP. In the second study, those with impaired preoperative respiratory function had significantly larger values for[Formula: see text].[Formula: see text] was as sensitive as parameters such as VD/VT, arterial to end-tidal CO2 tension difference (a-ET·Dco2), and volume pressure index (VPI) in prediting poor respiratory functions. We concluded that[Formula: see text] is a useful index for evaluating the phase III slope in CO2 elimination curves.