Renal vein oxygen saturation in renal artery stenosis

Renal vein oxygen-saturation was measured in 56 patients with arterial hypertension and unilateral stenosis or occlusion of the renal artery. Oxygen-saturation in blood from the ischaemic kidney (84.4%, range 73-93%) was significantly higher than that from the 'normal' contralateral kidney (81.2%, range 70-90%, P less than 0.001). In only six patients, the ischaemic kidney revealed a venous oxygen-saturation below the contralateral value (mean difference ischaemic-normal kidney 3.2%, range -6 to 15%). The results indicate that the oxygen uptake in the chronic ischaemic kidney is more decreased than its blood flow. This is probably due to decreased filtration fraction and filtered sodium with subsequent reduction in absolute tubular re-absorption of sodium ions.