NITROUS OXIDE

Inhalation gas with weak anaesthetic action but strong analgesic action

Dosage Forms

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Medical Gas

99.999%

Uses

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  • Maintenance of anaesthesia in combination with other anaesthetic agents and muscle relaxants
  • Analgesia for obstetric practice
  • Emergency management of injuries
  • Postoperative physiotherapy
  • Refractory pain in terminal illness

Dose and Duration

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Anaesthesia

Adult and child: nitrous oxide mixed with 25–30% oxygen

Analgesia

Adult and child: 50% nitrous oxide with 50% oxygen

Contraindications

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  • Middle ear occlusion
  • Arterial air embolism
  • Decompression sickness
  • Chronic obstructive airway disease
  • Emphysema
  • Demonstrable collection of air in pleural, pericardial or peritoneal space

Side Effects

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  • Nausea, vomiting
  • Megaloblastic anaemia
  • Reduced white cell formation on prolonged use
  • Peripheral neuropathy

Interactions

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  • Beta blockers e.g. atenolol, propranolol (possible severe hypotension and heart failure)
  • Chlorpromazine, fluphenazine, haloperidol (enhanced hypotensive effect)
  • Methotrexate (increased antifolate effect)
  • Verapamil (enhanced hypotensive effect and atrioventricular delay)

Pregnancy

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  • Can be used

Breast-feeding

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  • Can be used

⚠️ Caution

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  • May depress neonatal respiration if used in 3ʳᵈ trimester
  • Minimise staff exposure
  • Give additional oxygen for several minutes after stopping the flow of nitrous oxide to reduce risk of hypoxia
  • Do not give continuously for longer than 24 hours or more frequently than every 4 days without haematology monitoring and close supervision