Desaturation-distance ratio and the optimal diagnostic approach to the desaturators identification among copd patients

   Using ROC analysis among 118 COPD patients, depending on the desaturation-distance ratio (DDR), a comparative assessment of three diagnostic approaches to detecting «desaturators» was carried out: (1) by SpO₂ regression ≥ 4 % during the 6-minute walking test (6MWT) from baseline (preload) to the end level of blood oxygenation and/or by SpO₂ regression below 90 % by the end of 6 MWT (∆SpO₂base-end ≥ 4 % and/or up to SpO₂end < 90 %); (2) by regression of SpO₂ ≥ 4 % during 6 MWT from baseline (preload) to the minimum level of blood oxygenation and/or by regression of SpO₂ to the minimum value < 90 % during 6 MWT (∆SpO₂base-min ≥ 4 % and/or to SpO₂min < 90 %); (3) only by regression
of SpO₂ ≥ 4 % (∆SpO₂base-end ≥ 4 %). A comparison of the first two approaches revealed a significant advantage of the diagnostic approach ∆SpO₂base-end ≥ 4 % and/or up to SpO₂end < 90 %: AUC was 0.89 vs 0.84 with the second approach, the sensitivity level was 81 vs 62 % with identical specificity. In addition, in the case of an approach using the formula ∆SpO₂base-min ≥ 4 % and/or to SpO₂min < 90 %, overdiagnosis of exercise-induced desaturation (EID) hemoglobin by oxygen was detected – 61,9 % of «desaturators» vs 30,5 % of «desaturators» with the first diagnostic approach (p < 0.001). Taking into account the maximum values of AUC (0.94) and sensitivity (96 %), the high level of specificity (92 %), and the simplicity of identifying «desaturators» based on only one indicator, the optimal diagnostic approach was to identify «desaturators» according to the formula ∆SpO₂base-end ≥ 4 %. EID was associated with a DDR level ≥ 3.3 % m^-1. DDR ≥ 3.9 % m^-1 was associated with the need for an additional O2 flow during 6MWT to maintain a minimum acceptable SpO₂ value ≥ 88 % during exercise.

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