Retinal oxygen saturation in patients with systemic hypoxemia

To assess spectrophotometric oximetry across a broad range of arterial saturation levels and to study the effect of chronic systemic hypoxemia on retinal oxygen extraction. The study included 16 patients with Eisenmenger syndrome, a cyanotic cardiac defect, and 17 healthy volunteers. Oxygen saturation in selected major retinal arteries and veins was assessed using noninvasive spectrophotometric oximetry. Arterial blood gases were determined within 1 day of the ophthalmic examination in blood samples from the femoral artery. The retinal arterial oxygen saturation of 81% ± 9% (mean ± SD) in patients with Eisenmenger syndrome was subnormal and demonstrated more interindividual variation than the 93% ± 3% observed in healthy subjects (P < 0.001). A comparable difference was found for the respective retinal venous oxygen saturations of 44% ± 12% and 59% ± 5% (P < 0.001). Fractional arteriovenous oxygen extraction was comparable between the two groups (37% ± 6% and 34% ± 5%, respectively; P = 0.29). Retinal and femoral artery oxygen saturation were correlated (ρ = 0.82; P < 0.001), the former approximating the latter at least as well as fingertip oximetry. When compared to arterial blood gas analysis of blood samples drawn by arterial puncture, the gold standard in the field, fundus oximetry was found to be in good overall agreement with the arterial blood samples. Blood flow measurements will be needed to determine whether the systemic hypoxia is completely compensated, as suggested by oxygen extraction being comparable between the two groups.