Nitrous Oxide Limits — ORE Part 1 MCQ
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Correct answer: D — 70% N₂O (with minimum 30% O₂)
Explanation lettering: B = shown as A · C = shown as B · D = shown as C · A = shown as D
The maximum permitted concentration of nitrous oxide in inhalation sedation is 70%, paired with a minimum of 30% oxygen. This limit is mechanically enforced by the fail-safe systems built into all approved dental sedation equipment and is essential to prevent patient hypoxia. The 30% oxygen minimum ensures patients receive oxygen levels above ambient air (21%). Whilst 50% N₂O is commonly used clinically for routine sedation, option A specifies the regulatory maximum. Options B, D, and E (90%, 100%, 80%) represent unsafe concentrations that would result in inadequate oxygenation. Option C (50%) is correct for typical clinical titration but does not represent the maximum permitted.
Reference: Malamed SF. Nitrous oxide-oxygen administration: when safety features no longer are safe. J Dent Educ. 2012 Aug;76(8):1018-24. PMID: 22298554. https://pubmed.ncbi.nlm.nih.gov/22298554/