EVALUATION OF CAPNOGRAPHY IN NONINTUBATED EMERGENCY DEPARTMENT PATIENTS WITH RESPIRATORY-DISTRESS

Objective: To evaluate the ability of noninvasive capnographic measure ment of end-tidal CO2 tension (Petco(2)) to predict arterial CO2 tensi on (Paco(2)) in nonintubated ED patients with respiratory distress. Me thods: A prospective, nonblind study was performed in a level I trauma center/community teaching hospital ED. Participants included all noni ntubated adult patients with respiratory distress requiring measuremen t of arterial blood gases (ABGs); 29 patients were enrolled. Petco(2) was measured with a capnography monitor, using both baseline tidal vol umes and forced expiratory volumes. The bias between Petco(2) values a nd simultaneous measurements of Paco(2) by ABG was assessed. Results: Petco(2), measured with forced expiration, and Paco(2) agreed well, wi th bias (i.e., average difference) = 0.44 +/- 0.52 kPa (3.3 +/- 3.9 to rr). Petco(2) measured with the tidal volume breath produced an unacce ptably high bias of 0.82 +/- 0.70 kPa (6.1 +/- 5.2 torr). Levels of ag reement between Paco(2) and Petco(2) were similar for smokers and nons mokers and for men and women. The arterial-end-tidal CO2 tension (Pa-e tco(2),) difference was not related to Paco(2). Pa-etco(2) correlated with age (r = 0.473; p = 0.01), and was significantly higher in patien ts with pulmonary disease (1.32 +/- 0.56 kPa; 9.9 +/- 4.2 torr) than i t was in those without pulmonary disease (0.46 +/- 0.55 kPa; 3.5 +/- 4 .1 torr; p < 0.001). Conclusions: Noninvasive Petco(2) monitoring may adequately predict Paco(2) in nonintubated ED patients with respirator y distress who are able to produce a forced expiration. Petco(2) is le ss accurate for Paco(2) with tidal volume breathing and in patients wi th pulmonary disease.