Calculated arterial blood gas values from a venous sample and pulse oximetry: Clinical validation

BACKGROUND: Arterial blood gases (ABG) are essential for assessment of patients with severe illness, but sampling is difficult in some settings and more painful than for peripheral venous blood gas (VBG). Venous to Arterial Conversion (v-TAC; OBIMedical ApS, Denmark) is a method to calculate ABG values from a VBG and pulse oximetry (SpO(2)). The aim was to validate v-TAC against ABG for measuring pH, carbon dioxide (pCO(2)) and oxygenation (pO(2)). METHODS: Of 103 sample sets, 87 paired ABGs and VBGs with SpO(2) from 46 inpatients eligible for ABG met strict sampling criteria. Agreement was evaluated using mean difference with 95% limits of agreement (LoA) and Bland-Altman plots. RESULTS: v-TAC had very high agreement with ABG for pH (mean diff((ABG–v-TAC)) -0.001; 95% LoA -0.017 to 0.016), pCO(2) (-0.14 kPa; 95% LoA -0.46 to 0.19) and moderate to high for pO(2) (-0.28 kPa; 95% LoA -1.31 to 0.76). For detecting hypercapnia (PaCO(2)>6.0 kPa), v-TAC had sensitivity 100%, specificity 93.8% and accuracy 97%. The accuracy of v-TAC for detecting hypoxemia (PaO(2)<8.0 kPa) was comparable to that of pulse oximetry. Agreement with ABG was higher for v-TAC than for VBG for all analyses. CONCLUSION: Calculated arterial blood gases (v-TAC) from a venous sample and pulse oximetry were comparable to ABG values and may be useful for evaluation of blood gases in clinical settings. This could reduce the logistic burden of arterial sampling, facilitate improved screening and follow-up and reduce patient pain.