Repeatability of blood gas parameters in arterialized capillary blood among patients with chronic respiratory diseases: a differentiated approach to clinical evaluation

Introduction. To form a well-grounded judgment on changes in gas exchange over time during corrective oxygen therapy, instrumental diagnostic procedures, exercise testing, and assessment of pharmacological effects, it is important to know the repeatability of blood gas indicators, including all possible errors of measurement (technical, methodological and physiological). Aim. To investigate the repeatability of blood gas indicators and oxygen saturation in arterialized capillary blood among patients with chronic respiratory diseases (CRDs) to ensure an objective evaluation of observed changes. Materials and methods. A single-center observational prospective study included 200 patients over 18 years of age diagnosed with chronic respiratory diseases: 110/200 (55.0%) with various clinical forms of pulmonary tuberculosis, 58/200 (29.0%) with interstitial lung diseases, and 32/200 (16.0%) with chronic obstructive pulmonary disease. Two samples of arterialized capillary blood were collected at a 30-minute interval. Partial pressures of oxygen (PaO 2 ) and carbon dioxide (PaCO 2 ), as well as oxygen saturation (SaO 2 ), were analyzed using the Easy Blood Gas analyzer (Medica, USA). Repeatability, individual coefficient of variation, minimum significant change, and absolute and relative measurement errors for PaO 2 , PaCO 2 , and SaO 2 were calculated. Statistical processing was performed using MS Excel 2016 for Windows, IBM SPSS Statistics 23, and STATISTICA 10 with nonparametric methods. Results. The repeatability of PaO 2 results was higher than that of SaO 2 by more than twofold (3.67 vs 1.14), despite a strong correlation between these parameters. In contrast, under severe gas exchange disorders, the repeatability of PaO 2 and SaO 2 was almost identical (2.86 and 2.89, respectively). The repeatability value for PaCO 2 was 1.92 but increased to 4.16 in cases of moderate hypercapnia. Conclusion. In patients with chronic respiratory diseases, differences in arterialized capillary blood gas and oxygen saturation values of 3.67 mm Hg for PaO 2 , 1.14% for SaO 2 , and 1.94 mm Hg for PaCO 2 (upon repeated measurements in the same patient) should be considered clinically significant. Given the representative sample, inclusion criteria, distribution of data, 95% CI calculations, and precision of the measurement conditions, the authors propose that these findings can be applied to clinical practice.