Mathematically arterialised venous blood is a stable representation of patient acid–base status at steady state following acute transient changes in ventilation

Abstract

Hyper- or hypoventilation are commonly occurring stress responses to arterial puncture around the time of blood sampling and have been shown to rapidly alter arterial blood acid–base parameters. This study aimed to evaluate a physiology-based mathematical method to transform peripheral venous blood acid–base values into mathematically arterialised equivalents following acute, transient changes in ventilation. Data from thirty patients scheduled for elective surgery were analysed using the physiology-based method. These data described ventilator changes simulating ‘hyper-’ or ‘hypoventilation’ at arterial puncture and included acid–base status from simultaneously drawn blood samples from arterial and peripheral venous catheters at baseline and following ventilatory change. Venous blood was used to calculate mathematically arterialised equivalents using the physiology-based method; baseline values were analysed using Bland–Altman plots. When compared to baseline, measured arterial and calculated arterialised values at each time point within limits of pH: ± 0.03 and PCO 2 : ± 0.5 kPa, were considered ‘not different from baseline’. Percentage of values considered not different from baseline were calculated at each sampling timepoint following hyper- and hypoventilation. For the physiological method, bias and limits of agreement for pH and PCO 2 were -0.001 (-0.022 to 0.020) and -0.02 (-0.37 to 0.33) kPa at baseline, respectively. 60 s following a change in ventilation, 100% of the mathematically arterialised values of pH and PCO 2 were not different from baseline, compared to less than 40% of the measured arterial values at the same timepoint. In clinical situations where transient breath-holding or hyperventilation may compromise the accuracy of arterial blood samples, arterialised venous blood is a stable representative of steady state arterial blood.

Comparison of mathematically arterialised venous blood gas sampling with arterial, capillary, and venous sampling in adult patients with hypercapnic respiratory failure: a single-centre longitudinal cohort study

“…Data are lacking on the prevalence or impact. It was postulated recently that the v-TAC conversion from venous blood could mitigate the acute changes in the arterial baseline induced by a transient change in breathing pattern 19. We, therefore, conducted a post hoc analysis of our data set to consider the potential effect of transient changes in breathing pattern.…”

Venous to v-tac™: Challenging the routine use of a traditional ABG

“…The method evaluated further in this PhD project is the one by Rees et al (commercially called Roche v-TAC ™ , referred to as 'v-tac' in the dissertation) (43) which calculates arterial equivalents from peripheral venous blood and has been suggested for use in the ED (44,45) and pulmonary departments (46). This method employs physiology-based mathematical models, where it assumes good perfusion at the tissues, with little or no anaerobic metabolism across the tissue bed (details of the method are described in papers III and IV (3,4)). v-tac has been evaluated on acute patients (45,47), patients with COPD (44,48,49), respiratory failure (50) and those undergoing NIV treatment (47), and has been shown to function well within 2 standard deviations (SD) of ± 0.026 and ± 0.5 kPa for pH and PCO2 (48) when compared to measured arterial values; well within the limits of what Rang et al (37) reported as clinically acceptable.…”