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Experimental Retinal Vein Occlusion: Effect of Acetazolamide and Carbogen (95% O₂/5% CO₂) on Preretinal PO₂

From the Department of Ophthalmology, University Hospital of Geneva, Geneva, Switzerland.

PURPOSE. To evaluate the variations of preretinal oxygen partial pressure (PO₂) in normal and in ischemic postexperimental branch retinal vein occlusion (BRVO) areas, during normoxia, hyperoxia (100% O₂), and carbogen (95% O₂, 5% CO₂) breathing before and after intravenous injection of acetazolamide.

METHODS. Preretinal PO₂ measurements were obtained in intervascular retinal areas, distant from the retinal vessels of 13 anesthetized mini-pigs with oxygen-sensitive microelectrodes (10 µm tip diameter) introduced through the vitreous cavity by a micromanipulator. The microelectrode tip was placed <50 µm from the vitreoretinal interface in the preretinal vitreous. PO₂ was measured continuously for 10 minutes under systemic normoxia, hyperoxia, and carbogen breathing. A BRVO was induced with an argon green laser, and oxygen measurements were repeated under normoxia, hyperoxia, and carbogen breathing, before and after intravenous injection of acetazolamide (500 mg bolus).

RESULTS. In hyperoxia, a moderate nonsignificant preretinal PO₂ increase in both normal (PO₂ = 2.20 ± 4.16 mm Hg; n = 25) and ischemic retinas (PO₂ = 4.30 ± 3.57 mm Hg; n = 16) was measured in spite of a substantial increase in systemic PaO₂. Carbogen breathing induced a significant increase in systemic PaCO₂ and a higher systemic PaO₂ than hyperoxia. Furthermore, it significantly increased the preretinal PO₂ in normal areas (PO₂ = 19.37 ± 16.41 mm Hg; n = 26), and in ischemic areas (PO₂ = 14.94 ± 8.53 mm Hg; n = 14). Intravenous acetazolamide did not affect the preretinal PO₂. Acetazolamide induced an increase of the preretinal PO₂ to a greater extent when it was associated with carbogen breathing (PO₂ = 15.15 ± 9.15 mm Hg; n = 7) than when it was combined with hyperoxia (PO₂ = 6.96 ± 4.49 mm Hg; n = 7).

CONCLUSIONS. Carbogen breathing significantly increased preretinal PO₂ in normal and in ischemic postexperimental BRVO areas of mini-pigs. The concomitant use of acetazolamide injection and carbogen breathing or hyperoxia could restore an appropriate oxygenation of BRVO areas.

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