Comparison of End-Tidal, Arterial, Venous, and Transcutaneous P.

Background: We investigated the measurement of end-tidal partial pressure of carbon dioxide (P ) with a capnometer in patients with respiratory failure, and we determined whether this technique could provide an alternative to measurement of P using arterial blood gas analysis in the clinical setting.

Methods: We measured P in subjects with hypoxemic and hypercarbic respiratory failure using a capnometer. We simultaneously measured P , venous partial pressure of carbon dioxide (P ), and transcutaneously measured partial pressure P (P ). We analyzed agreements among these parameters with Bland-Altman analysis. We obtained 30 samples from subjects with hypoxemic respiratory failure and 30 samples from subjects with hypercarbic respiratory failure.

Results: Thirty subjects with hypoxemic respiratory failure and 18 subjects with hypercarbic respiratory failure participated in this study. Significant relationships were found between P and P , between P and P , and between P and P . Bland-Altman analysis of P and P in all subjects revealed a bias of 6.48 mm Hg (95% CI 4.93-8.03, < .001) with a precision of 6.01 mm Hg. Bland-Altman analysis of P and P with hypoxemic respiratory failure revealed a bias of 5.14 mm Hg (95% CI 3.35-6.93, < .001) with a precision of 4.80 mm Hg. Bland-Altman analysis of P and P in subjects with hypercarbic respiratory failure revealed a bias of 7.83 mm Hg (95% CI 5.27-10.38, < .001) with a precision of 6.83 mm Hg.

Conclusions: P can be measured simply using a capnometer, and P measurements can estimate P . However, the limits of agreement were wide. Therefore, care providers must pay attention to the characteristics and errors of these devices. These results suggest that measurement of P might be useful for screening for hypercarbic respiratory failure in the clinical setting.