Tamponades for vitreoretinal surgery

View PDF 

Gas tamponades

One of the early gases investigated as a tamponade material was sulphur hexafluoride. In the 1970s Abrams et al5 monitored the gas bubble composition as a function of time for initial injection of pure sulphur hexafluoride gas in rabbit eyes. Over a period of 96 hours the gas concentration of sulphur hexafluoride fell to around 3 per cent and with replacement by an equilibrium mixture of oxygen, nitrogen and carbon dioxide. Preferential diffusion of more mobile smaller gas molecules into the sulphur hexafluoride gas bubbles results in their initial expansion as the entrained gas pressure increases. This is an undesirable characteristic for gas tamponades where a target gas concentration is now usually set at a limit concentration to prevent bubble expansion. For sulphur hexafluoride this value is typically 14 per cent and for perfluoropropane 16 per cent. Values of gas mixture in excess of these values can result in elevated intraocular pressures.