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Experimental retinal vein occlusion: effect of acetazolamide and carbogen (95% O2/5% CO2) on preretinal PO2.

Research paper by Jean-Antoine C JA Pournaras, Ioannis K IK Petropoulos, Jean-Luc JL Munoz, Constantin J CJ Pournaras

Indexed on: 29 Sep '04Published on: 29 Sep '04Published in: Investigative ophthalmology & visual science



Abstract

To evaluate the variations of preretinal oxygen partial pressure (Po(2)) in normal and in ischemic postexperimental branch retinal vein occlusion (BRVO) areas, during normoxia, hyperoxia (100% O(2)), and carbogen (95% O(2), 5% CO(2)) breathing before and after intravenous injection of acetazolamide.Preretinal Po(2) measurements were obtained in intervascular retinal areas, distant from the retinal vessels of 13 anesthetized mini-pigs with oxygen-sensitive microelectrodes (10 microm tip diameter) introduced through the vitreous cavity by a micromanipulator. The microelectrode tip was placed <50 microm from the vitreoretinal interface in the preretinal vitreous. Po(2) 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).In hyperoxia, a moderate nonsignificant preretinal Po(2) increase in both normal (DeltaPo(2) = 2.20 +/- 4.16 mm Hg; n = 25) and ischemic retinas (DeltaPo(2) = 4.30 +/- 3.57 mm Hg; n = 16) was measured in spite of a substantial increase in systemic Pao(2). Carbogen breathing induced a significant increase in systemic Paco(2) and a higher systemic Pao(2) than hyperoxia. Furthermore, it significantly increased the preretinal Po(2) in normal areas (DeltaPo(2) = 19.37 +/- 16.41 mm Hg; n = 26), and in ischemic areas (DeltaPo(2) = 14.94 +/- 8.53 mm Hg; n = 14). Intravenous acetazolamide did not affect the preretinal Po(2). Acetazolamide induced an increase of the preretinal Po(2) to a greater extent when it was associated with carbogen breathing (DeltaPo(2) = 15.15 +/- 9.15 mm Hg; n = 7) than when it was combined with hyperoxia (DeltaPo(2) = 6.96 +/- 4.49 mm Hg; n = 7).Carbogen breathing significantly increased preretinal Po(2) 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.