The effect of carbon dioxide on oxygen-induced retinopathy in the neonatal rat

Purpose. Hypercarbia has been suggested as a risk factor for retinopathy of prematurity. We investigated the effect of raised inspired carbon dioxide on oxygen-induced retinopathy in the neonatal rat. Methods. Newborn rats raised in expanded litters (n = 25 each) were exposed to cycles of hyperoxia (80% O₂) and hypoxia (10% O₂) for 7 days, followed by room air recovery for 5 days. During cyclic oxygen exposure, 3 Litters (n = 75) were exposed to 10% CO₂ (PaCO₂ 78 mm Hg ± 6; mean ± SD) and 3 litters (n = 75) were exposed to 0.2% CO₂ (PaCO₂ 45 mm Hg ± 7). Animals were sacrificed on day 13 and retinae were analyzed using fluorescein perfusion and ADPase staining techniques. Results. Neovascularization occurred in 85% of rats exposed to high CO₂ compared to 52% of rats exposed to low COP (p = 0.001). The severity of neovascularization, in clock hours, was also greater in the rats exposed to high CO₂ (p < 0.001). Conclusions. Exposure to high CO₂ results in an increased incidence and severity of neovascularization in a rat model for oxygen-induced retinopathy. Our results support the suggestion that hypercarbia may be a risk factor for retinopathy of prematurity.