Abstract
ObjectiveTo determine if non-invasive oxygenation indices, namely peripheral capillary oxygen saturation (SpO2)/fraction of inspired oxygen (FiO2) and partial pressure of alveolar oxygen (PAO2)/FiO2 may be used as effective surrogates for the partial pressure of arterial oxygen (PaO2)/FiO2. Also, to determine the SpO2/FiO2 and PAO2/FiO2 values that correspond to PaO2/FiO2 thresholds for identifying acute respiratory distress syndrome (ARDS) in patients following coronary artery bypass graft (CABG) surgery.MethodsA prospective derivation-validation cohort study in the Open-Heart ICU of an academic teaching hospital. Recorded variables included patient demographics, ventilator settings, chest radiograph results, and SPO2, PaO2, PAO2, SaO2, and FiO2. Linear regression modeling was used to quantify the relationship between indices. Receiver operating characteristic (ROC) curves were used to determine the sensitivity and specificity of the threshold values.ResultsOne-hundred seventy-five patients were enrolled in the derivation cohort, and 358 in the validation cohort. The SPO2/FiO2 and PAO2/FiO2 ratios could be predicted well from PaO2/FiO2, described by the linear regression models SPO2/FiO2 = 71.149 + 0.8PF and PAO2/FiO2 = 38.098 + 2.312PF, respectively. According to the linear regression equation, a PaO2/FiO2 ratio of 300 equaled an SPO2/FiO2 ratio of 311 (R2 0.857, F 1035.742, < 0.0001) and a PAO2/FiO2 ratio of 732 (R2 0.576, F 234.887, < 0.0001). The SPO2/FiO2 threshold of 311 had 90% sensitivity, 80% specificity, LR+ 4.50, LR- 0.13, PPV 98, and NPV 42.1 for the diagnosis of mild ARDS. The PAO2/FiO2 threshold of 732 had 86% sensitivity, 90% specificity, LR+ 8.45, LR- 0.16, PPV 98.9, and NPV 36 for the diagnosis of mild ARDS. SPO2/FiO2 had excellent discrimination ability for mild ARDS (AUC ± SE = 0.92 ± 0.017; 95% CI 0.889 to 0.947) as did PAO2/FiO2 (AUC ± SE = 0.915 ± 0.018; 95% CI 0.881 to0.942).ConclusionsPaO2 and SaO2 correlated in the diagnosis of ARDS, with a PaO2/FiO2 of 300 correlating to an SPO2/ FiO2 of 311 (Sensitivity 90%, Specificity 80%). The SPO2/ FiO2 ratio may allow for early real-time rapid identification of ARDS, while decreasing the cost, phlebotomy, blood loss, pain, skin breaks, and vascular punctures associated with serial arterial blood gas measurements.
Highlights
Circulatory and cardiovascular diseases (CVD) remain the leading cause of death globally [1]
Partial pressure of O2 in arterial blood (PaO2) and SaO2 correlated in the diagnosis of acute respiratory distress syndrome (ARDS), with a PaO2/Fraction of inspired oxygen (FiO2) of 300 correlating to an SPO2/ FiO2 of 311 (Sensitivity 90%, Specificity 80%)
The SPO2/ FiO2 ratio may allow for early real-time rapid identification of ARDS, while decreasing the cost, phlebotomy, blood loss, pain, skin breaks, and vascular punctures associated with serial arterial blood gas measurements
Summary
Circulatory and cardiovascular diseases (CVD) remain the leading cause of death globally [1]. The severity-of-illness scoring systems that are commonly used in medical ICUs have not been very useful in predicting death in these patients, as high scores are often not associated with poor outcome [6,7,8]. This may in part be due to our ability to normalize physiology by means of pharmacologic and/or mechanical support. The Berlin definition is only slightly better than its predecessor for ARDS prognostication (receiver operating characteristic [ROC] area under the curve [AUC], 0.577 vs 0.536) This may be partially related to the dependence of both definitions on PaO2/FiO2 as the primary measure of ARDS severity. We seek to determine the threshold values for SpO2/FiO2 (S/F) and PAO2/FiO2 (PA/F) that correlate with P/F ratios consistent with ARDS (mild 201– 300; moderate 101–200; severe ≤100 mmHg)
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