Abstract
BACKGROUND:
Transcutaneous carbon dioxide (PtcCO2 ) monitoring is being used increasingly to assess acute respiratory failure. However, there are conflicting findings concerning its reliability when evaluating patients with high levels of PaCO2 . Our study evaluates the accuracy of this method in subjects with respiratory failure according to the severity of hypercapnia.
METHODS:
We included subjects with respiratory failure, admitted to a respiratory intermediate care unit, who required arterial blood gas analysis. Simultaneously, PtcCO2 was measured using a digital monitor. Relations between PaCO2 and PtcCO2 were assessed by the Pearson correlation coefficient. Bland-Altman analysis was used to test data dispersion, and an analysis of variance test was used to compare the differences between PaCO2 and the corresponding PtcCO2 at different levels (level 1, <50 mm Hg; level 2, 50–60 mm Hg; level 3, >60 mm Hg).
RESULTS:
Eighty-one subjects were analyzed. The main diagnosis was COPD exacerbation (45%). PtcCO2 correlated well with PaCO2 (r2 = 0.93, P < .001). Bland-Altman analysis showed a mean PaCO2 − PtcCO2 difference of 4.9 ± 4.4 with 95% limits of agreement ranging from −3.6 to 13.4. The difference between variables increased in line with PaCO2 severity: level 1, 1.7 ± 3.2 mm Hg; level 2, 3.7 ± 2.8; level 3, 6.8 ± 4.7 (analysis of variance, P < .001).
CONCLUSIONS:
Our study showed an acceptable agreement of PtcCO2 monitoring with arterial blood gas analysis. However, we should consider that PtcCO2 underestimates PaCO2 levels, and its accuracy depends on the level of hypercapnia, so this method would not be suitable for acute patients with severe hypercapnia.
Keywords
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