Accuracy of Capnography in Nonintubated Surgical Patients

Previous studies have reported mixed results when correlating etCO 2 and PaCO 2 in mechanically ventilated patients with underlying respiratory disease. However, the utility and accuracy of capnography in nonintubated patients, without chronic pulmonary disease, has received little attention. We studied 25 nonintubated surgical patients to (1) examine the correlation between PaCO 2 and etCO 2 and (2) describe the relationship between dead space (Vd/Vt), venous admixture and P(a-et)CO 2 . End tidal CO 2 was lower than PaCO 2 by an average of 3.6 mm Hg. Regression analysis found a close correlation between dead space and the P(a-et)CO 2 gradient (r = 0.77, p 2 can be useful for continuously monitoring the respiratory status of nonintubated spontaneously breathing patients weaned from mechanical ventilation. This may be of particular value in trauma victims and in selected surgical patients without underlying respiratory disease in whom other injuries require continued critical care.