Background: In spontaneously breathing patients, the differences between arterial PaCO2and end-tidal CO2(EtCO2) and the influence of bronchial obstruction have not clearly established. Material/Methods: This was a prospective observational study. Patients (n=120) were classified according to spirometric criteria into groups with normal, mild, moderate, and severe obstruction. Arterial blood gases and capnography were performed in two ways: with a tidal volume (Vt) and a non-forced maximal expiration maneuver. Pearson correlation coefficients (r) between PaCO2and capnographic values were determined for the entire cohort and the subgroups. A concordance study was performed with Bland-Altman analysis. Results: Comparison of PaCO2and EtCO2measured at Vt showed a significant correlation (r=0.722, p<0.01) for the entire cohort, but with a significant mean infra-estimation: P(a-et)CO2=5.2±4.4 mmHg, p<0.05. Analysis of subgroups: At Vt, P (a-et) CO2was 1.7±2.9 mmHg (p-ns) in patients with normal spirometry, being maximal in the group with greater obstruction (8.2±5.6 mmHg, p<0.05). At maximal expiration, the comparison between PaCO2and EtCO2showed a significant correlation (r=0.88, p<0.001), but a significant lack of concordance for the entire cohort (P (a-et) CO2=-4.8±4 mmHg, p<0.05) and subgroups. Finally, comparison of PaCO2and mean EtCO2values showed a significant correlation (r=0.74, p<0.001) and concordance (P (a-et) CO2= 0.2±3.3 mmHg, p=ns) for the entire cohort and subgroups. Conclusions: Capnographic results at Vt are accurate predictors of true PaCO2only in patients without bronchial obstruction. The maneuvers of slow maximal expiration overestimate PaCO2in all groups. The best concordance was obtained comparing PaCO2with mean EtCO2. © Med Sci Monit, 2008.
|Journal||Medical Science Monitor|
|Publication status||Published - 1 Sep 2008|
- End-tidal CO 2
- Tidal volume