The effects of enflurane on ocular blood flow

Although general anesthesia is frequently chosen for eye surgery or experimental studies of ocular blood flow, there are few data available describing its effects on ocular blood flow. In a previous study in cats, we reported that enflurane produced significant increases in preretinal oxygen tension, indicating an increase in oxygen availability in the retina. To examine whether this effect was due to an increase in retinal or choroidal blood flow, we used radioactively labeled 15 microns microspheres of Ce 141, Sn 113, Ru 103, or Nb 95, to measure ocular blood flow in cats during enflurane anesthesia. In 10 adult cats, retinal blood flow measured 75 +/- 13, 90 +/- 9 and 88 +/- 11 ml x 100 g-1 x min-1 (mean +/- S.E.M.) at 0.5, 1.0, and 1.5 MAC enflurane, respectively (1 MAC is the concentration at which 50% of subjects do not move in response to a standardized stimulus). Corresponding values for choroidal blood flow were 1275 +/- 124, 876 +/- 106 and 842 +/- 102 ml x 100 g-1 x min-1 (mean +/- S.E.M.) at 0.5, 1.0, and 1.5 MAC enflurane, respectively. The decrease in choroidal blood flow was significant between 0.5 and 1.0 MAC. These results differ from those in our previous investigation of the effects of halothane on ocular blood flow. With halothane, retinal blood flow increased and choroidal blood flow decreased throughout the entire dose range (0.5, 1.0, and 1.5 MAC). We conclude that inhalational anesthetic agents produce significant but different effects upon ocular blood flow.