Nitrous Oxide

What it is and how it works

Nitrous oxide is a weak inhalational anaesthetic with marked analgesic properties, thought to act mainly through NMDA-receptor antagonism and release of endogenous opioids; it has rapid onset and offset because of its low blood solubility.

Indications

Maintenance of general anaesthesia in combination with other anaesthetic agents and oxygen; analgesia and sedation for short painful procedures.

Dosage and administration (summary)

Administered by inhalation through a calibrated anaesthetic machine in concentrations individualised by the anaesthetist, always with at least 25–30% oxygen.

Contraindications

Pneumothorax, air embolism, decompression sickness, bowel obstruction, recent intraocular injection of gas (e.g. SF6 or C3F8), middle-ear surgery, severe head injury with impaired consciousness, and vitamin B12 deficiency.

Warnings and precautions

Expands gas-filled body cavities. Prolonged or repeated exposure inactivates vitamin B12, causing megaloblastic anaemia and neuropathy (myeloneuropathy). Diffusion hypoxia can occur at the end of administration, so oxygen should be given; occupational exposure must be minimised by scavenging.

Pregnancy

Avoid prolonged exposure in early pregnancy; widely used for analgesia in labour.

Storage and supply

Store cylinders upright in a well-ventilated, dry area away from heat and combustible materials, in accordance with medical gas regulations.

Source: reference summary prepared from the EU SmPC/EPAR, BNF and WHO Model Formulary. The approved product information in Iran governs.