Interaction of intraocular air and sulfur hexafluoride with nitrous oxide: a computer simulation.

The diffusion dynamics of intravitreal gas bubbles injected during retinal reattachment procedures were studied using a mathematical model. This model predicts the effect of 70 per cent nitrous oxide anesthesia on the volume of the intravitreal bubble. The calculations indicate that when 70 per cent nitrous oxide administration is continued following intravitreal gas injection, there is a rapid, almost threefold increase in the volume of the injected bubble. When nitrous oxide is discontinued at the time of intravitreal injection, a maximum initial bubble expansion of only 35 per cent occurs. If nitrous oxide is discontinued 15 minutes prior to intravitreal injection, the mathematical model indicates that, at most, there will be a 15 per cent expansion of the bubble volume. The model calculations indicate that there is little difference in intravitreal bubble volume whether air of 100 per cent oxygen is used during the anesthetic. The two major factors that influence intravitreal bubble volume are the mixture of air or SF6 injected and the pattern of nitrous oxide use during anesthesia. These factors can be controlled. The importance of bubble volume changes on intraocular pressure and retinal blood flow also depend on other factors such as scleral rigidity, blood pressure, the presence of glaucoma, and the size of the injected gas bubble relative to the total vitreal volume.