A surgeon plans fluid-air exchange followed by gas tamponade for a superior rhegmatogenous retinal detachment. Which concentration of sulfur hexafluoride (SF6) is considered 'non-expansile' when mixed with air?
- A Approximately 8%
- B Approximately 30%
- C Approximately 18 to 20% ✓
- D Approximately 50%
Correct answer: C. Approximately 18 to 20%
Explanation
Pure SF6 doubles its volume in the eye, so a concentration that neither expands nor shrinks is roughly half of pure, about 18 to 20%, which matches residual air after a complete fluid-air exchange. Concentrations above this expand the bubble and raise intraocular pressure; below this the bubble resorbs too quickly. For B3F8 the equivalent non-expansile concentration is around 12 to 14%, a common distractor.
Reference: Ryan's Retina, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.