Roche v-TAC

Software application to calculate arterial blood gas values from venous blood

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The new alternative to arterial sampling for blood gas measurement


Arterial blood gas is the gold standard for acid-base and blood gas testing in critical care. However, arterial punctures are complex, painful for the patient and come with a risk of side effects such as haematoma and infections.1,2

Over the recent years there has been an increasing trend towards the use of venous blood, as it is more easily accessible and sample collection is less painful for the patient.3 While clinical parameters for acid-base measurements (pH, pCO2 and bicarbonate) are largely similar between arterial and venous sampling, the venous measurement of oxygenation (pO2, sO2) is significantly different and therefore limits its use.4

Roche v-TAC software helps to overcome these limitations.


Arterial blood gas values from a venous blood sample


Roche v-TAC software calculates arterial blood gas (ABG) values from venous peripheral blood gas measurement, combined with arterial oxygen saturation (SpO2), measured by a pulse oximeter.

The precision of the v-TAC calculated values is comparable to that of repeated ABG values for blood gas parameters, including pH, pCO2, pO2 (up to 10 kPa), HCO3 and base excess (BE).5

Roche v-TAC may contribute to clinical, workflow and patient benefits

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Enable workflow improvements with easy access to blood gas testing6

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Transfer the task of blood gas testing from doctor/specialist to other staff groups, such as nurses6

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Improve the speed of providing blood gas values for timely patient monitoring that may reduce the length of stay and improve clinical compliance7

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Combine blood sampling for venous blood gas with routine blood sampling to decrease the need for separate punctures6

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Reduce the need for painful arterial blood samples and potential side effects6

How does it work? 


It is very simple to operate Roche v-TAC in daily clinical practice. The software can be used with the cobas b 123 POC system (configurations 3 and 4) and cobas b 221 system from Roche. Additionally, it can work seamlessly with blood gas analyzers from other leading manufacturers.

After implementation, the operational workflow is as follows:

  1. Collect the venous blood sample for blood gas analysis and the corresponding SpO2
  2. Select v-TAC on the blood gas analyser to activate conversion to arterial values and enter the SpO2 value
  3. The v-TAC software calculates the arterial blood gas values which instantly become available to the clinician

Scientific background


The v-TAC Software is based on an advanced algorithm and mathematical models of acid-base and blood chemistry by Rees & Andreassen.

Watch the v-TAC scientific explanatory video and learn how the v-TAC software calculates arterial blood gas values from peripheral venous blood gas measurements, combined with pulse oximetry measurement of arterial oxygen saturation.


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Learn how Roche v-TAC can help guide timely clinical decisions for COVID-19 patients.



HCO3: bicarbonate; kPa: kilopascal; pH: power of hydrogen; pCO2: partial pressure of carbon dioxide; pO2: partial pressure of oxygen; POC: point of care




  1. Word Health Organisation (2010). Article available from [Accessed May 2020]
  2. Hambsch et al. (2015). Clin Transl Sci 8, 857–870
  3. McKeever et al. (2016). Thorax 71, 210-215
  4. Byrne et al. (2014). Respirology 19, 168-175
  5. Toftegaard et al. (2009). Emerg Med J 26, 268-272
  6. Ekström et al. (2019). PLoS ONE 14(4):e0215413
  7. Kamperidis et al. (2018). Thorax 73:A250

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