Evaluation of Capnography in Nonintubated Emergency Department Patients with Respiratory Distress

Abstract

Objective: To evaluate the ability of noninvasive capnographic measurement of end‐tidal CO2 tension (Petco2) to predict artenal CO2 tension (Paco2) in nonintubated ED patients with respiratory distress Methods: A prospective, nonblind study was performed in a level I trauma centerkommunity teaching hospital ED. Participants included all nonintubated adult patients with respiratory distress requiring measurement of arterial blood gases (ABGs): 29 patients were enrolled Petcoz was measured with a capnography monitor. using both baseline tidal volumes and forced expiratory volumes. The bias between Petco? values and simultaneous measurements of Paco2 by ABG was assessed Results: Petco, measured with forced expiration, and Pace? agreed well, with bias (i.e, average difference) = 044 ± 0.52 kPa (33 ± 3.9 torr). Petco2 measured with the tidal volume breath produced an unacceptably high bias of 0.82 ± 0.70 kPa (6.1 ± 5.2 torr). Levels of agreement between Paco2 and Petco2 were similar for smokers and nonsmokers and for men and women. The arterial‐end‐tidal CO2 tension (Pa‐etco2) difference was not related to Paco2 Pa‐etco2 correlated with age (r = 0.473; p = 0.01), and was significantly higher in patients with pulmonary disease (132 ± 0S6 kPa; 99 ± 42 torr) than it was in those without pulmonary disease (0.46 ± 055 kPa, 3.5 ± 4.1 torr, p < 0.001). Conclusions: Noninvasive Petcoz monitoring may adequately predict Paco2 in nonintubated ED patients with respiratory distress who, are able to produce a forced expiration. Petco2 is less accurate for Paco2 with tidal volume breathing and in patients with pulmonary disease © 1995 Society for Academic Emergency Medicine