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

Abstract

Arterial blood gases (ABGs) are the gold standard for assessment of blood acid-base status. However, an arterial puncture is painful and has many complications. Venous blood was proposed as a surrogate for arterial blood, but it differs based on sample location and is less reliable outside the normal physiological range. An alternative method has been developed involving physiology-based models, called v-tac™ which has been shown to transform peripheral venous values to their arterialised equivalents. It has been tested in patients in the emergency and pulmonary departments and has been shown to work well within clinically acceptable limits. ABGs can be rapidly influenced by changes in ventilatory patterns. Such changes could be present at the time of blood sampling and could alter the results of the blood gas analysis. Similar responses of venous blood or v-tac to changes in ventilation have not yet been explored. In addition, differences between peripheral and central venous blood in terms of their responses to ventilatory changes or with respect to v-tac conversions has not been evaluated. This PhD project aimed to evaluate the responses of arterial, peripheral, and central venous blood to acute changes in ventilation, simulating the changes observed around the time of blood sampling. In addition, the use of v-tac following acute ventilatory changes was evaluated, as well as its ability to transform values of central venous blood to arterialised equivalents. The results show that arterial blood responds rapidly to acute changes in ventilation, while venous blood displays a more delayed and dampened response. As a consequence of using the stable venous blood, v-tac was able to accurately calculate arterialised values, thereby better representing the steady-state/baseline arterial values, when compared to the rapidly changed acid-base parameters measured in the arterial blood. This means that if there is any suspicion of a change in ventilatory pattern when collecting an arterial blood sample, it might be prudent to draw a venous blood sample and use the v-tac converted values instead of the traditional ABG, to avoid risks of patient misclassification while evaluating their acid-base status. In addition, the PhD project has shown that the performance of v-tac is as good as other models in its ability to transform central venous values. As central venous blood is evaluated most amongst the critically ill, further research needs to be done to evaluate the use of v-tac amongst the critically ill.