OBI Medical
FAQ
  • Q: How does v-TACTM work?

    A: v-TACTM is a method implemented in software. The principle of the method is as follows. Peripheral venous blood differs from arterial blood by its content of oxygen and carbon dioxide. Arterial blood values can therefore be calculated by removing CO2 and adding O2 in a constant ratio (RQ) that reflects the metabolism of tissue. The method simulates the addition of oxygen to the peripheral venous blood until simulated oxygen saturation matches that measured non-invasively from a pulse oximeter. The amount of oxygen added in this simulation is then used to calculate the amount of CO2 removed, and consequently the complete arterial oxygen and acid-base status can be determined.

  • Q: Does v-TACTM replace existing blood gas instruments?

    A: No, v-TACTM does not replace existing blood gas instruments. In fact, v-TACTM software works with existing blood gas instruments on the market. 

  • Q: Does v-TACTM work with all existing blood gas instruments?

    A: v-TACTM software works with existing blood gas analysers on the market, as long as the instrument is capable of transmitting the blood gas values over a known and supported protocol.

  • Q: Is v-TACTM still useful and validated if there is a condition of excess acid, such as diabetic ketoacidosis, lactic acidosis or salicylate poisoning?

    An excess of acid will present itself as a negative base excess in the blood. Our mathematical models account for changes in base excess. The v-TACTM method assumes that the value of base excess is the same in the arterial and venous blood samples. Systemic, whole-body changes in acid-base balance resulting in acid production will result in negative base excess in blood measured at any site. Systemic changes are therefore not a problem for the method.

    There may, however, be local differences of BE in arterial and venous blood in some conditions. For example, mixed venous or central venous blood drains from many organs. These organs may produce quite varying quantities of acid and, in this case, arterial and mixed or central venous blood will not have the same BE.

    For peripheral venous samples it is unlikely that there are large differences between arterial and venous BE values due to local acid production. This is particularly true if the peripheral venous site is warm and well perfused, which is easily identifiable by clinical inspection or by the presence of a pulse oximetry signal. In a warm, well-perfused extremity, the likelihood of local tissue anaerobic metabolism is small, and BE values should be the same in both arterial and venous blood at this site. 

    Use of the v-TACTM method is therefore not limited to patient acid-base status when using peripheral venous blood. 

  • Q: Does v-TACTM work for patients in a state of "warm shock"?

    In patients with warm shock it is common for blood to pass quickly by some tissue without substantial metabolism taking place. If this is the case, then the peripheral venous blood sample will be very close to the arterial, both in terms of O2 and CO2. As v-TACTM works on mathematically adding O2 and removing CO2, and this occurs in ratio, then the method will still work in patients experiencing shock. The advantage of the method in this case is that one does not need to consider whether the patient is in shock or not (in terms of interpreting the venous blood gasses), as the nature of the method automatically compensates for this. Many data sets have been seen where this is true, even in patients without shock.

  • Q: Does v-TACTM work for patients in a state of "cold shock"?

    A: In patients in a state of cold shock, the peripheral circulation shuts down, while the body tries to maintain circulation in the central system. In such cases, the peripheral limb will not be well perfused and peripheral arterial blood will not be representable for central arterial blood, meaning SpO2 cannot be measured either using a pulse oximeter. In patients with cold shock, v-TACTM is not recommended.

  • Q: Is v-TACTM sensitive to variation in the measured SpO2?

    A: v-TACTM is generally very robust to variation in the SpO2 measurement. If SpO2 is overestimated compared to the real value (saO2), the calculated pH will be +0.0015 per +1%, while the pCO2 will be -0.3 [mmHg] (-0.04 [kPa]) per +1%. The opposite if SpO2 is -1%. For pO2, the impact on the v-TACTM calculated arterial values will depend on the actual level of SpO2. At SpO2 levels ≤ 96% v-TACTM is robust to variation in SpO2. Request data plots for more information. 

  • Q: Does v-TACTM work if the patient is a smoker?

    A: Yes, the v-TACTM method works also if the patient is a smoker. However, heavy smoking may cause fCOHb to elevate up to approximately  0.10 (severe CO poisening up to 0.20 or more), and this may affect the SpO2 reading. Clinical studies report possible false-high SpO2 readings due to smoking of (mean) +3% at fCOHb levels > 0.02. A 3% false-high SpO2 reading will affect the pH with approximately +0.004 and the pCO2 with approximately -0.75 [mmHg] (-0.10 [kPa]). The impact on pO2 vary depending on the actual SpO2 level. Request data plots for more information.

  • Q: Does v-TACTM work also for patients with high or low temperatures?

    A: v-TACTM converts the venous blood gas results to arterial blood gas results based on the same temperature for which the venous blood gas results were measured. Normal practice is to measure blood gas at 37 degrees Celsius, meaning that if the patient has a low or high temperature, the blood gas analyser will warm up or cool the blood to 37 degrees Celsius before analysis. In some cases, the patient temperature may be entered manually, in which case the blood gas instrument calculates at this temperature. v-TACTM has been validated with 37 degrees Celsius.

  • Q: Is v-TACTM sensitive to air bubbles in the blood sample?

    A: Air bubbles may cause in-accuracy in the venous blood gas analysis for the same reasons that apply for arterial blood gas. Therefore, the syringe should be emptied of air bubbles as quickly as possible.

  • Q: Does v-TACTM work on children?

    A: v-TACTM has been validated on adults age 18 and above. OBI Medical is working on validating the method on children. Contact OBI Medical for more information.

  • Q: What is the advantage of v-TACTM compared to capillary blood gas?

    A: Capillary blood sampling is available for obtaining arterialized venous blood. This method, however, involves ‘mechanical’ rather than ‘mathematical’ arterialization, performed by administering local vasodilation cream or warming the sampling site, which, in contrast to the v-TACTM method, makes clinical application cumbersome and time-consuming. In addition, venous blood is routinely taken for other purposes, whereas capillary sampling is not routine. Application of the v-TACTM method may therefore not require extra punctures, risk of blood spill etc.

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