O2 content of blood sampled from different venous compartments of the rat.

Male Sprague-Dawley rats (n = 18) weighing 548 +/- 30 g were anesthetized with pentobarbital sodium (40-65 mg/kg body wt ip), intubated via tracheotomy, and mechanically ventilated. After exposure of the great vessels in the thorax, blood was withdrawn from the pulmonary artery (PA), right ventricle (RV), right atrium (RA), inferior vena cava (IVC), and ascending aorta. The O2 content of these blood samples was determined by direct measurements and/or was calculated from the measured hemoglobin concentration, percent of O2 saturation, and PO2. Ventilatory rates and the inspired fraction of O2 were manipulated to vary the mixed venous O2 content (CvO2) of blood withdrawn from the PA from 1.4 to 12.9 ml O2/dl blood (vol%). Our results demonstrate that O2 contents of blood withdrawn from the PA, RV, and RA are not significantly different from one another (CPAO2 - CrvO2 = -0.02 +/- 0.25 and CPAO2 - CRAO2 = -0.07 +/- 0.41 vol%, n = 28, P greater than 0.05); however, the O2 content of blood withdrawn from the IVC is significantly lower than that withdrawn from the PA (CPAO2 - CIVCO2 = 2.11 +/- 0.34 vol%, P less than 0.001). In addition, the directly measured O2 contents were equivalent to those that were calculated. These results suggest that the O2 content of blood found in the RA and RV of the rat are indicative of the O2 content of blood found in the PA. Thus blood sampled from these areas can be used to estimate mixed venous oxygenation.