Mathematical Arterialization of Capillary Blood for Blood Gas Analysis in Critically III Patients

Background: In clinical practice, capillary blood taken from hyperemized earlobes (CBG(E)) or fingertips (CBG(F)) is frequently used as substitute for arterial blood (ABG) for blood gas analysis. While there is a close agreement between ABG and CBG(E)/CBG(F) regarding pH and pCO(2), pO(2) is often underestimated by CBG. Recently, a software tool (v-TAC (R); Roche Diagnostics, Risch-Rotkreuz, Switzerland) has been developed to calculate ABG values based on a peripheral venous blood gas analysis supplemented with peripheral oxygen saturation. Objective: Here we investigate whether v-TAC can also be used to calculate ABG values from capillary blood samples. Methods: Patients (n = 85) with an indwelling arterial line were included in the study. A reference ABG sample (ABG(1)) was obtained, followed by CBG(E), CBG(F), and finally a second ABG (ABG(2)). Results of CBG(E)/CBG(F) before and after mathematical arterialization by v-TAC (aCBG(E)/aCBG(F)) were compared to ABG(1). Results: After mathematical arterialization by v-TAC, the mean bias in pO(2) between ABG(1) and CBG(E) went down from 5.24 mm Hg (95% limit of agreement [95% Loa -14.19 to 24.67) to 0.18 mm Hg (95% LoA: -11.84 to 12.20) and was in a similar range as the mean bias between ABG(1) and ABG(2) (0.39 mm Hg [95% LoA: -13.46 to 14.24]). Differences in pH and pCO(2) between arterial and capillary samples were small before and after mathematical arterialization. Very similar results were obtained when using fingertip instead of earlobe capillary blood. Conclusion: In summary, v-TAC can be used for mathematical arterialization of capillary blood samples for blood gas analysis resulting in increased diagnostic accuracy for pO(2). (C) 2022 S. Karger AG, Basel

Automated summary

The study investigated whether the v-TAC software tool can be used to calculate ABG values from capillary blood samples. The results showed that after mathematical arterialization by v-TAC, the discrepancy in pO(2) between capillary blood and arterial blood was significantly reduced and comparable to the discrepancy between two arterial blood samples. The differences in pH and pCO(2) were small, and similar results were obtained when using fingertip blood instead of earlobe blood.