Abstract
We evaluated the use of end-tidal PCO₂ (Petco₂) as an indication of changes in Paco, in 24 adult patients being weaned from mechanical ventilation following cardiac surgery. METHODS: Patients were weaned by synchronous intermittent mandatory ventilation (SIMV) and T-piece trials. After each change in the weaning process (SIMV rate, T-piece trial), arterial blood gases were obtained from an indwelling catheter, and the Petco, and respiratory rate were recorded. All patients were hemodynamically stable, and all pulse oximeter saturations were ≥ 90% throughout the weaning period. A total of 113 data sets were collected. RESULTS: The correlation between Paco, and Petco, was r = 0.82, although the Paco, overestimated the Petco, by 4.0 ± 3.7 torr. There was no significant difference between changes in Paco, and changes in Petco, (p = 0.63). However, in 43% of cases the change in Petco, incorrectly indicated the direction of change in Paco, When Pco, changes of ≥ 5 torr occurred, Petco, incorrectly indicated the direction of change in 30% of the cases. The respiratory rates displayed by the capnograph (15 ± 5/min) were similar to the patients' actual respiratory rates (16 ± 5/ min). CONCLUSIONS: Although changes in Petco, were not statistically different from changes in Paco, Petco, did not precisely indicate changes in Paco, during weaning from mechanical ventilation following cardiac surgery. Based on these results, we do not recommend the routine use of Petco, as a noninvasive indicator of Paco, during weaning from mechanical ventilation following cardiac surgery.
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