Mixed venous and arterial blood in bovine coccygeal vessel samples for blood gas analysis

Bovine coccygeal (median, caudal) vessel samples are not always Venous in origin but may be arterial or a mixture of venous and arterial blood. Results of blood gas analysis of blood samples collected from 39 cows were consistent with typical venous, mixed venous-arterial, or typical arterial blood. This observation was made while establishing reference intervals for a new blood gas instrument. The pO(2) and the oxygen saturation of hemoglobin (SO,) were most reflective of the amount of arterial blood contamination in the sample, but pCO(2) and pH also were altered. The pO(2) values ranged from 21 to 127 mm Hg, and SO2 ranged from 35% to 100%. The mean pCO(2) in venous type samples was 46.3 mm Hg compared to 36.7 mm Hg in arterial type samples. The mean pH in venous type samples was 7.42 compared to 7.47 in arterial type samples.