Nitrous oxide (N2O) is contraindicated in a patient with pneumocephalus following posterior fossa surgery. The minimum interval before N2O can be safely re-introduced after craniotomy closure is approximately:

• A 2–3 hours
• B 12–24 hours
• C 2–3 weeks
• D 3–5 days ✓

Explanation

Pneumocephalus resolves at a rate determined by nitrogen reabsorption; air introduced intracranially is absorbed within 3–5 days. Introducing N2O before this window causes it to diffuse into the gas-filled space (N2O is 34 times more soluble than nitrogen), rapidly expanding pneumocephalus and raising intracranial pressure. Air in other closed spaces (e.g., pneumothorax, bowel) resolves faster, but intracranial air persists longer due to the rigid skull. Waiting 2–3 weeks is unnecessarily conservative for routine cases.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.