EFFECT OF SAMPLING SITE ON FEMORAL VENOUS-BLOOD GAS VALUES

To examine whether the tip of the femoral vein catheter used for sampl ing femoral venous PO2 during cycling exercise is contaminated by skin or saphenous vein blood, we studied 6 healthy volunteers [21.7 +/- 0. 7 (SD) yr] during three identical incremental exercise tests while bre athing room air on the same day. Femoral venous blood was sampled simu ltaneously from two catheters inserted into the femoral vein but advan ced in opposite directions (7 cm distally and 5 cm proximally). Blood sampling for measurements of PO2, PCO2, pH, hemoglobin concentration, and oxyhemoglobin saturation was done simultaneously from both cathete rs in duplicate at rest, at 60% of maximum workload (60% W), and at ma ximum symptomlimited exercise (100% W). Temperature was measured with a thermistor probe placed in the proximal catheter. At rest, distal PO 2 was significantly lower than that measured proximally (24.9 +/- 4.3 vs 30.8 +/- 6.1 mmHg, respectively; P < 0.004), but no differences wer e found during exercise (60% W, 23.6 +/- 3.4 vs. 24.5 +/- 3.6 mmHg; 10 0% W, 26.0 +/- 3.6 vs. 25.5 +/- 2.8 mmHg, respectively). Comparison of blood temperatures between proximal and distal sites of sampling in t wo subjects showed negligible differences. Intrasubject coefficient of variation of distal femoral venous PO2 over the three bouts of exerci se was 11.5% (2.9 mmHg) at rest, 5.9% (1.4 mmHg) at 60% W, and 5.6% (1 .5 mmHg) at 100% W. Mean differences in distal PO2 between duplicate s amples were 0.5 +/- 1.4 mmHg at rest, 0.1 +/- 0.8 mmHg at 60% W, and 0 .6 +/- 0.9 mmHg at 100% W. We conclude that the site of femoral venous sampling may influence the analysis of muscle O-2 transport at rest b ut not at greater than or equal to 60% maximal O-2 uptake, suggesting negligible contributions to O-2 indexes from nonexercising tissues und er these conditions.