Retinal and choroidal blood flow response to hyperoxemia after severe hypoxemia in the newborn piglet

To investigate the effect of hyperoxemia on the ocular circulation after a severe hypoxemic insult (8% O2 until base excess reached -20 mmol/l), we randomly reoxygenated newborn piglets with 100% (study group, n = 8) or 21% O2 (control group, n = 10). Retinal (RBF) and choroidal blood flow (ChBF) were measured with radioactive microspheres. The hypoxemic insult did not change RBF, while ChBF significantly decreased. However, a marked reduction in both retinal (RDO2) and choroidal oxygen delivery (ChDO2) was observed, probably resulting in hypoxia both in the inner and outer retina. At 5 and 20 min of reoxygenation a similar hyperemic response in the retina was seen in both groups. RDO2 also increased significantly and no significant differences between the 2 groups could be demonstrated. We found no indication of retinal vasoconstriction during hyperoxemia. We speculate that the vasodilating effect of the preceding hypoxemia overrules the vasoconstrictive effect of the retinal vessels normally found during hyperoxemia.