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Introduction: The amount of oxygen in blood is an important measure of lung function. There are three ways to quantify the amount of oxygen in blood: 1) the oxygen tension (PO2); 2) the percent of hemoglobin saturated with oxygen (HbO2); and 3) the absolute content of oxygen in the blood (ContO2). PO2 is commonly measured. HbO2 and ContO2 are usually calculated from the normal human oxyhemoglobin relationship, but can be measured directly. The canine curve is similar to, but not the same as, that of humans. The purpose of this study was to compare, in dogs, direct measurements of HbO2 and ContO2 with analyzer-calculated values derived using the human oxyhemoglobin curve, and with hand-calculated values derived using a canine oxyhemoglobin curve.

Materials And Methods: Arterial and jugular venous samples from 17 healthy dogs were analyzed by an ABL 705 blood gas and electrolyte analyzer, an OSM3 co-oximeter, and a LexO2con oxygen content analyzer. HbO2 was calculated from the measured PO2 using a published formula based on normal canine data (Reeves, 1982), and compared to measured and analyzer-calculated values. ContO2 values were calculated, and compared to measured and analyzer-calculated values. Means and standard deviations were compared by analysis of variance for repeated measures. Differences were considered significant at p<0.05.

Results: Arterial HbO2 determined by the ABL 705 factory-programmed algorithm, reported by the OSM3 co-oximeter, and calculated from Reeves' canine formula were significantly different (97.1±0.57, 98.2±0.58, and 96.6±0.74, respectively). The calculated canine HbO2 was significantly lower than that measured by the OSM3 or calculated by the ABL for both arterial and jugular venous samples. Calculated and measured arterial and venous ContO2 were similar, as were arterial-venous ContO2 differences. However, values derived from the calculated canine HbO2 (canine-calculated) resulted in the greatest arterial-venous ContO2 difference.

Conclusion: ABL-calculated and canine-calculated HbO2 were similar to measured values. Likewise, ABL-calculated, canine-calculated, and OSM3-calculated ContO2 were very similar to measured values. Although some of the values generated by the different methods are statistically significantly different, these differences are unlikely to be clinically important in the healthy dog.