[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Inhaled anaesthetics](https://durgical.com/en/pharmacology/classes/inhaled-anaesthetics/) › Nitrous oxide

[Pharmacology](https://durgical.com/en/pharmacology/) · [Inhaled anaesthetics](https://durgical.com/en/pharmacology/classes/inhaled-anaesthetics/)

# Nitrous oxide

Weak anaesthetic gas but a good analgesic, combined with oxygen and other anaesthetics. It expands air-filled spaces and inactivates vitamin B12.

Updated 2026-11-01

- Class: [Inhaled anaesthetics](https://durgical.com/en/pharmacology/classes/inhaled-anaesthetics/)
- Receptor: NMDA glutamate receptor (and two-pore-domain potassium channels)
- ATC code: N01AX13
- WHO Model List of Essential Medicines

Also called: Dinitrogen monoxide, N2O

## Mechanism of action

Nitrous oxide is a colourless gas, poorly soluble in blood, that mainly blocks the NMDA receptor and activates some two-pore-domain potassium channels; unlike halogenated agents, it barely acts on the GABA-A receptor. It is a weak anaesthetic, so it is not enough on its own for surgery, but it is a good analgesic and reduces the amount of other anaesthetics needed. Its rapid uptake concentrates a halogenated agent given at the same time and speeds induction (second gas effect).

- Inhaled, it equilibrates very quickly because of low solubility
- Blocks the NMDA receptor: analgesia and weak anaesthesia
- Adds to the halogenated agent (lower MAC)
- When stopped, it floods the alveoli and dilutes oxygen

## Pharmacokinetics

**Absorption**
Through the lungs; very poorly soluble in blood: fast onset and recovery.

**Metabolism**
Practically not metabolised.

**Elimination**
Almost all is exhaled unchanged through the lungs.

## Indications

- Adjunct to general anaesthesia with other anaesthetics
- Inhaled analgesia and sedation for brief procedures, mixed with oxygen

## Adverse effects

### Common

- Raised intracranial blood flow and pressure
- Raised venous tone and pulmonary vascular resistance
- Blunted ventilatory response to hypoxia

### Serious (rare, important)

- Diffusion hypoxia when stopped if 100% oxygen is not given
- Expansion of air-filled spaces: pneumothorax, blocked middle ear, obstructed bowel loop, intraocular or intracranial gas bubbles, air embolism
- Vitamin B12 inactivation with megaloblastic anaemia and neuropathy, especially with malnutrition, B12 deficiency or alcoholism and with recreational use

## Contraindications

- Pneumothorax, bowel obstruction, blocked middle ear, intraocular gas bubble or intracranial air
- Vitamin B12 deficiency, malnutrition or alcoholism (high risk of B12 toxicity)
- Pulmonary hypertension (it worsens it)

## Key interactions

**Halogenated anaesthetics**
Lowers the concentration needed and speeds induction (second gas effect).

**Opioids**
Together they usually lower blood pressure and cardiac output.

## What is monitored

- Oxygen saturation during and after use
- Inspired oxygen concentration (always adequate)
- With repeated exposure: blood count and signs of neuropathy

## Administration and safety

- Always mixed with enough oxygen; never as the only gas.
- At the end, give 100% oxygen for a few minutes to prevent diffusion hypoxia.

## Nursing care

- Before: rule out pneumothorax, bowel obstruction, recent ear surgery or eye surgery with gas.
- During and after: watch saturation and level of consciousness.
- Ask about symptoms of B12 deficiency (tingling, weakness) and recreational use.

## Pregnancy and breastfeeding

It has little effect on uterine muscle; its effect on vitamin B12 and DNA synthesis is a concern with repeated exposure, so it is kept to brief uses.

## Memory aid

Nitrous oxide: «laughing gas that inflates bubbles and switches off B12».

## Test yourself

Think of the answer, then tap the question to see it.

## Why is 100% oxygen given when nitrous oxide is stopped?

Because nitrous oxide leaves the blood quickly into the alveoli and dilutes the oxygen: diffusion hypoxia.

## Why is nitrous oxide contraindicated in pneumothorax?

It enters the air space faster than nitrogen leaves, raising its volume or pressure and worsening the pneumothorax.

## How does nitrous oxide cause megaloblastic anaemia?

It oxidises the cobalt of vitamin B12 and inactivates it as the cofactor of methionine synthase, which disturbs DNA synthesis.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/nitrous-oxide/)

## Related drugs

- [Sevoflurane](https://durgical.com/en/pharmacology/sevoflurane/)
- [Oxygen](https://durgical.com/en/pharmacology/oxygen/)
- [Ketamine](https://durgical.com/en/pharmacology/ketamine/)

[← Back to the class: Inhaled anaesthetics](https://durgical.com/en/pharmacology/classes/inhaled-anaesthetics/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 24 (McGraw Hill, 2023); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=N01AX13) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/pharmacology/nitrous-oxide/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/nitrous-oxide/