RESUMO
INTRODUCTION: Arterial blood gas analysis (ABG) is the gold standard test for carbon dioxide measurement. End-tidal PCO2 (PetCO2 ) and transcutaneous PCO2 (PtcCO2 ) are noninvasive alternative methods. OBJECTIVE: To examine the use of PetCO2 and PtcCO2 as PaCO2 surrogates in awake children. METHODS: A prospective observational study. Consecutive awake children in a stable condition referred to the Sleep Unit of Hospital de Pediatría Dr. J. P. Garrahan with suspected or confirmed sleep-related respiratory disorders 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. The sample size was calculated considering a mean difference ≤3 mmHg as clinically acceptable. RESULTS: Sixty-eight sample sets were obtained from 67 patients. The 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 /PtcCO2 was r = .6 and .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 CO2 might be a good screening tool to detect hypercapnia in awake children.
