Can you achieve “arterialization” of the venous blood in a dog with normal cardiovascular status by heating its paw to 37C (=98.6F) for measurement of blood gas variables?
In both human and veterinary medicine, venous blood samples have been used to estimate acid-base balance as an alternative to arterial blood samples. In human medicine, a technique called “arterialization” of the dorsal hand vein is established, where warming the hands to 42-43°C (=107-109.4F) for 10-15 minutes makes venous blood more similar to arterial blood.
Shiroshito et al., JVIM 2023 (Tokyo University of Agriculture and Technology) performed a study on eight healthy dogs to compare the accuracy of cephalic and saphenous venous blood samples, “arterialized” by continuous heating of the paws to 37°C by an incandescent lamp, with arterial blood for measuring blood gas variables. This experiment was performed at baseline and after they experimentally induced metabolic and respiratory acid-base disorders. The study found good agreement of arterialized cephalic/saphenous blood with arterial blood in terms of pH, [HCO3], and BE values, while significant difference and poor agreement between arterial and saphenous/cephalic with respect to PO2 values. Cephalic and saphenous PCO2 measurements were slightly higher (by around 3-4 mm Hg) compared to arterial PCO2. This difference was within clinically acceptable limits for pH, [HCO3], and BE, but slightly higher for PCO2. The PO2 difference was clinically unacceptable.
VETEMCRIT comments: This study had a robust design, however the main limitation was the fact that the authors did not compare the arterial samples with regular (i.e. “non-heated”) blood samples to identify the true impact of “arterilization” on the venous blood gas results. Furthermore, the utilization of general anesthesia could have potentially enhanced the connection between arterial and “arterialized” venous blood parameters. This might have been achieved by diminishing vasoconstriction through the suppression of central thermoregulation. Consequently, this could have prompted the natural “arterialization” of venous blood. As a result, the robust correlation observed in this study between arterial blood and “arterialized” venous samples could be attributed to the combined effects of various factors. In addition, there was a very poor correlation between “arterialized” venous and true arterial blood PO2 levels, therefore this technique can’t be recommended in patients who need an accurate assessment of arterial blood oxygenation (e.g. pets with respiratory distress including those receiving mechanical ventilation).
My personal take-away: Heating paws before getting a venous sample for blood gas analysis may not be warranted at this time since the variable of interest on the ARTERIAL blood gas is usually PaO2 that had a very poor correlation with the venous “arterialized” sample. A regular venous sample is usually sufficient for acid-base analysis in clinical patients unless PO2 has to be accurately evaluated. Also, remember that pets in shock will have an increased gap between venous and arterial pCO2 (e.g. normal gap is about 2-5 mm Hg, while the shock state may lead to the gap approaching 5-30 mm Hg).
The link to the full paper: https://onlinelibrary.wiley.com/doi/full/10.1111/jvim.16745
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