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

Date Published: April 12, 2019

Publisher: Public Library of Science

Author(s): Magnus Ekström, Anna Engblom, Adam Ilic, Nicholas Holthius, Peter Nordström, Ivar Vaara, Raffaele Serra.


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 (SpO2). The aim was to validate v-TAC against ABG for measuring pH, carbon dioxide (pCO2) and oxygenation (pO2).

Of 103 sample sets, 87 paired ABGs and VBGs with SpO2 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.

v-TAC had very high agreement with ABG for pH (mean diff(ABG–v-TAC) -0.001; 95% LoA -0.017 to 0.016), pCO2 (-0.14 kPa; 95% LoA -0.46 to 0.19) and moderate to high for pO2 (-0.28 kPa; 95% LoA -1.31 to 0.76). For detecting hypercapnia (PaCO2>6.0 kPa), v-TAC had sensitivity 100%, specificity 93.8% and accuracy 97%. The accuracy of v-TAC for detecting hypoxemia (PaO2<8.0 kPa) was comparable to that of pulse oximetry. Agreement with ABG was higher for v-TAC than for VBG for all analyses. 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.

Partial Text

Arterial blood gases (ABG) are essential in everyday clinical care for evaluating acid-base status (pH), level of carbon dioxide (PaCO2) and oxygenation (PaO2) in patients with cardio-respiratory disease and severe illness. ABG is the current gold standard for assessing the need for acid-base correction, ventilator therapy and treatment with supplemental oxygen.[1–3]

Between 21 Aug and 31 Oct 2017, a total 103 complete sample sets of consecutive ABG and VBG were collected. When evaluated against the quality criteria, 16 sets were excluded due to unphysiological values (n = 5), air bubbles in the syringe (n = 4), time between ABG and VBG > 5 min (n = 4), hyperventilation between the tests (n = 2) or SpO2 < 75% (n = 1). The main findings are that v-TAC has very high agreement with an ABG for level of pH and level of pCO2 and moderate to high agreement for pO2. v-TAC was more accurate than VBG for all measures.   Source:


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