Leveraging the venous to arterial conversion (v-TAC) algorithm in blood gas testing to help improve patient care

Blood gas analysis is a crucial diagnostic that enables clinicians to understand respiratory, circulatory, and metabolic diseases. It offers insights into the patient's partial pressure of oxygen (pO2) and partial pressure of carbon dioxide (pCO2) as well as pH balance, which is also critical for ventilator therapy or treatment with supplemental oxygen.¹

Both arterial blood gas (ABG) and venous blood gas (VBG) analysis are used by clinicians to make clinical decisions. However, ABG is considered the gold standard method for blood gas analysis due to its superiority over VBG specifically for making decisions based on pCO2 and pO2 levels.¹

Yet, ABG draws are very challenging. While important for aiding diagnosis and a variety of treatment interventions including non-invasive ventilation, arterial punctures can only be performed by physicians or trained healthcare providers and may only be available to patients eligible for the procedure. This can lead to complex workflows and significant delays in treatment.² Furthermore, compared to VBG sampling, ABG sampling is more invasive and painful, potentially leading to bleeding, hematoma, thrombosis, and infection, and has lower first-draw success rates.^3,4

To address the problems associated with arterial punctures, a method known as the venous to arterial conversion (v-TAC) algorithm has been developed. v-TAC software calculates ABG values from peripheral VBG measurements and arterial oxygen saturation (SpO2) measurements using pulse oximetry in hemodynamically stable patients (age 18 and above). 

Since venous sampling and pulse oximetry are less invasive and less complex procedures to perform than arterial sampling, lab professionals should consider implementing v-TAC for calculating ABG. v-TAC offers a significant advantage that helps reduce the need for arterial punctures, helping improve the patient experience while not compromising the quality and accuracy of the obtained information for diagnosis.

While VBG has utility for specific indications, ABG is the recommended method for making decisions based on pCO2 and pO2 levels. ABG remains the gold standard, critical for fast and accurate diagnosis and treatment strategies for patients, especially those in critical respiratory situations.^1,5

Based on clinically validated studies, v-TAC may offer considerable advantages for lab professionals and healthcare organizations overall:^1,3,6-9

• Rapid patient screening in the emergency department, cardio-respiratory, and pulmonary wards: VBG draws and pulse oximetry measurements are quicker to perform than ABG and do not need physician intervention. v-TAC could enable more rapid patient screening, especially in settings that require fast decision making.

• Accurately evaluating pCO2 and pO2 and monitoring patient’s treatment response: VBG alone does not accurately measure pCO2 and pO2. v-TAC can better inform on these blood gas levels, from the initial diagnosis to the monitoring of the patient’s response.

• Reducing the use of arterial lines: Many healthcare organizations do not have the resources to consistently utilize arterial lines in patients. v-TAC could offer an alternative approach by using VBG sampling and pulse oximetry in instances where arterial lines are only present for arterial blood gas sampling.

• Decreasing the need for repeated arterial punctures: To help reduce patient discomfort, v-TAC could decrease the need for multiple arterial punctures and potential associated side effects.

• Improving operational workflow and cost savings for healthcare organizations: VBG sampling and pulse oximetry can be performed quickly by other healthcare personnel, such as nurses. Furthermore, arterial punctures have lower first-draw success rates and this can all lead to lengthy workflows and delays in patient treatment. v-TAC can help streamline workflows, and at the same time, provide a more accurate profile of the patient’s blood gas values. This can ultimately lead to cost savings for health systems.

Several clinical studies among different patient populations and settings have validated the use of v-TAC.

Ekström and colleague's findings indicate that v-TAC shows very high agreement with ABG for assessing pH and pCO2 levels, outperforming VBG across all measures. While less accurate for pO2, v-TAC’s agreement with ABG was comparable to or better than consecutive ABGs, suggesting its potential utility in routine acid-base and blood gas evaluations, with a reduced need for arterial sampling.¹

Another study published in 2023 in adult patients with hypercapnic respiratory failure compared v-TAC with ABG, capillary, and venous sampling.³ Similar values were found between v-TAC and ABG for pCO2 and pH values. Additionally, the investigators found that v-TAC sampling had the highest first-time success rate of 88% and was significantly less painful than ABG sampling.³ 

In a recent meta-analysis evaluating the performance and reliability of v-TAC among 811 samples from 12 studies conducted in a variety of settings, Shastri and associates found that v-TAC had a similar agreement in arterial values for pH, pCO2, and pO2, pointing to the possibility of using v-TAC to replace arterial punctures for evaluating ABG.⁹

Arterial draws for blood gas measurements are an integral part of diagnostics. They are the gold standard within health systems but can be challenging to perform.^1,5 These challenges can potentially interrupt efficient operational workflow and lead to delays in treatments within all healthcare settings, from the ICU and hospitals to emergency rooms and point-of-care settings. v-TAC can help fill this gap by offering healthcare organizations a method to accurately measure blood gas values without the need for ABG sampling and still provide crucial information to clinicians to make better and faster patient treatment strategies.

With v-TAC, there is an opportunity to forgo arterial sampling, using VBG coupled with pulse oximetry to calculate ABG values. By doing so, lab leaders can incorporate this software with their existing blood gas analyzers (where applicable) and offer clinicians and other healthcare providers a less-invasive, effective method for analyzing blood gas. This method has the potential to replace ABG tests and improve the quality of patient care.

Watch the recent ASPIRE webinar with Professor Stephen Rees to learn more about calculating v-TAC from physiology-based mathematical models.