Nitrous oxide cannot be used as the sole anaesthetic agent for surgical procedures at sea level because:

• A It is rapidly degraded by soda lime to a nephrotoxic compound
• B It has such high blood solubility that induction would take hours
• C It produces profound respiratory depression at anaesthetic doses
• D Its minimum alveolar concentration exceeds 100%, so even pure nitrous oxide will not prevent movement in 50% of patients ✓

Explanation

The MAC of nitrous oxide is approximately 104%, meaning that at sea level even 100% inspired concentration cannot reach 1 MAC in the alveoli once diluted by other gases and uptake. It therefore serves only as a carrier and adjuvant. Its blood:gas coefficient of 0.47 makes it fast rather than slow, and respiratory depression is minimal, which kills the other distractors.

Reference: Morgan and Mikhail's Clinical Anesthesiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.