Entonox Contraindications — MFDS Part 1 MCQ

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ModeratePharmacologyEntonox ContraindicationsMFDS Part 1

A cooperative adult is being assessed for self-administered Entonox (50% nitrous oxide and 50% oxygen) during a short dental procedure. Which history is a contraindication because nitrous oxide can enlarge a closed gas space?

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Correct answer: D — A current pneumothorax

A current pneumothorax is a contraindication to Entonox. Nitrous oxide enters enclosed gas spaces rapidly, increasing their volume or pressure and potentially enlarging a pneumothorax and worsening lung collapse. The same principle applies to conditions such as bowel obstruction, severe bullous emphysema, decompression illness and recent intraocular gas injection. Controlled hypertension, uncomplicated type 2 diabetes and well-controlled asthma without current respiratory compromise are not contraindications in themselves. Dental phobia is a potential indication for conscious sedation or analgesia, provided the patient can understand instructions, cooperate and self-administer the gas safely. Therefore, A is the single best answer.

Reference: University Hospitals Sussex NHS Foundation Trust. Entonox, section 'Is Entonox unsafe to take if you have certain medical conditions?', reviewed 26 January 2025. https://www.uhsussex.nhs.uk/resources/entonox/