Objectives: Arterial blood gas measurements are not always immediately available despite their potential relevance to management of mechanically ventilated patients. Retrospective and prospective studies have validated the non-linear imputation of PaO2/FIO2 from SpO2/FIO2, predominantly in USA. In this study, the objective was to validate the non-linear imputation algorithm among mechanically ventilated patients in the Chinese population.
Method: Mechanically ventilated patients admitted to the emergency departments or ICUs at two participating hospitals in China were enrolled prospectively. At the time of a clinical arterial blood gas being drawn, SpO2, oximeter waveform characteristics, receipt of vasopressor, and skin pigmentation were simultaneously recorded. For the various imputation methods, we calculated both imputation error and the area under the curve for patients meeting criteria for acute respiratory distress syndrome (PaO2/FIO2 ≤ 300) and moderate-severe acute respiratory distress syndrome (PaO2/FIO2 ≤ 150).
Result: We studied 663 arterial blood gases from 646 patients; 177 (26%) arterial blood gases were associated with SpO2 less than or equal to 96%. Non-linear imputation had lower mean absolute error than linear imputation method when SpO2 was less than or equal to 96% (p<0.001). At the PaO2/FiO2 threshold of 300 or less, non-linear imputation AUC (0.90 95% CI 0.85-0/95) was not significantly higher than the AUCs of linear and log-linear imputation methods (0.88 95% CI 0.82-0.94). The same result was shown at the PaO2 /FiO2 threshold of 150 or less. For patients with a threshold SpO2 of 96% or less, AUC analysis yielded similar results between non-linear vs. linear and log-linear imputations.
Conclusions: In this cohort of mechanically ventilated patients, non-linear imputation was not superior to linear and log-linear imputations for patients with SpO2 of 96% or less. All strategies performed similarly in estimating PaO2/FIO2 from SpO2/FIO2.