Nitrous oxide diffuses into closed gas spaces faster than nitrogen can exit. Which of the following surgical scenarios is an ABSOLUTE contraindication to N2O use because of this property?

• A Laparoscopic cholecystectomy
• B Middle ear surgery with tympanoplasty
• C Open inguinal hernia repair
• D Vitreoretinal surgery with intraocular SF6 gas tamponade ✓

Explanation

N2O has a blood:gas partition coefficient of 0.47 and diffuses into closed gas spaces 34 times faster than nitrogen exits. Intraocular gas tamponades (SF6, C3F8) used in vitreoretinal surgery represent an absolute contraindication; N2O diffusion into the gas bubble can cause dangerous intraocular pressure elevation and graft failure. Middle ear surgery is a relative contraindication (risk of tympanic membrane disruption). Laparoscopic surgery is a relative consideration but not absolute. N2O must be avoided for at least 5–10 weeks after intraocular gas injection.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.