The effect of raised inspired carbon dioxide on developing rat retinal vasculature exposed to elevated oxygen.

Hyperoxia is a risk factor for retinopathy of prematurity (ROP), a blinding disease in infants. However, ROP develops in human infants without raised arterial oxygen levels, such as in cyanotic congenital heart disease. In these infants raised pCO2 may be a risk factor. We investigated the effect of inspired CO2 on oxygen induced retinopathy in the rat. 56 newborn Sprague-Dawley rats were exposed to high cyclical O2 for seven days. In a control group, 27 rats were exposed to negligible CO2 by the use of soda lime. In the high CO2 group, 29 rats were exposed to elevated CO2 by omitting soda lime from their chambers. Rats in both groups had a recovery period of three days in room air following cyclical O2 exposure. On the eleventh day all rats were sacrificed after intracardiac injections of fluorescein under deep anesthesia and the retinae were dissected and flat mounted for fluorescent microscopy. The ratio of vascularized:total retinal area was calculated using computer assisted image analysis. In the high CO2 group 62% +/- 7% SD of the retina was vascularized vs. 81% +/- 7% in low CO2 group (p < 0.001). Elevated inspired CO2 results in pronounced retardation of retinal vascular development in neonatal rats exposed to fluctuating raised oxygen.