![]() ![]() Add 0.035 to the venous pH to estimate the arterial pH. In conditions such as DKA, it is probably reasonable to follow the pH response to treatment with VBGs. The venous pH tends to be more acidic than the arterial pH. The venous pH correlates well with the arterial pH. This is probably where the VBG is of most use but there are still limitations. However, the absolute value of pCO 2 on the VBG above this range correlates poorly with the paCO 2 and cannot be used to monitor the response to treatment in a CO 2 retainer. (100% sensitivity reported, so, at least in studies, it does not appear to miss any cases) If the pCO 2 on the VBG is above the normal arterial range (ie >45 mmHg, >6 kPa) the patient has CO 2 retention. This has an important impact on treatment. In patients with COPD we need to detect the presence of CO 2 retention. The VBG is of no value in assessing oxygenation status. The pO 2 on a VBG bears no relationship to the paO2. VBGs are useful if you know how to interpret them and have a knowledge of their limitations.Īn ABG has a number of uses, the VBG can be substituted for some of these uses but not for others. In addition, obtaining ABGs carries well known risks. VBGs are popular as it is far less painful for the patient to obtain a venous sample compared to an arterial sample. A VBG is obtained by placing a venous sample in the arterial blood gas analyser. There is currently a plague of ‘venous’ blood gases (VBG) in clinical practice. The readout from the machine quotes normal values based on the assumption that the sample analysed is arterial (an ABG). Arterial blood gas analysers are designed to measure multiple components in the arterial blood. ![]()
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