Validation of end-tidal PCO2 and transcutaneous PCO2 as surrogates of
arterial PCO2 in awake children
Arterial blood gas analysis (ABG) is the gold standard test for carbon
dioxide measurement. End-tidal PCO2 (PetCO2) and transcutaneous PCO2
(PtcCO2) are non-invasive alternative methods. Objective: to examine the
use of PetCO2 and PtcCO2 as PaCO2surrogates in awake children. Methods:
Prospective observational study. Consecutive awake children in stable
condition referred to the Sleep Unit of Hospital de Pediatría Prof. Dr.
J. P. Garrahan with suspected or confirmed SRRD requiring ABG were
included. PetCO2 and PtcCO2 were recorded simultaneously during arterial
puncture. PetCO2 and PtCO2 values were compared with PaCO2. Correlation
coefficient and Bland-Altman analysis were applied. Sample size was
calculated considering a mean difference ≤ 3 mmHg as clinically
acceptable. Results: 68 sample sets were obtained from 67 patients.
Median age was 9.11 years (0.23-18.76). During 94.1% of the procedures
patients breathed spontaneously, 30% needed multiple punctures and 92%
resulted in pain. Median (IQR) PaCO2 (mmHg) was 36.3 (31.45; 40.90),
PetCO2 33.0 (29;39) and PtcCO2 38.8 (32.95;43.32). Correlation and
agreement for PaCO2/PetCO2 and PaCO2/PtcCO2was: r= 0.6 and0.9, and media
of bias=2.83(-9.97;15.64) and-1.88 (-9.01;5.24), respectively.
Hypercapnia(PaCO2>45.0 mmHg) was present in 8/68 (11.8%)
samples. Sensitivity, specificity, positive predictive value and
negative predictive value to detect hypercapnia with PetCO2 was 38
%,98%,75% and 92%, respectively, and with PtcCO2, 100%, 90%, 57%
and 100%, respectively. Conclusion: PtcCO2 showed better agreement with
PaCO2 than PetCO2,.but because of the wide dispersion of values, neither
method can replace the gold standard. Transcutaneous CO2might be a good
screening tool to detect hypercapnia in awake children.