Oxygen !
Essential medical gas that corrects hypoxaemia. It is adjusted to a saturation target: too much harms the lung and the preterm retina.
Updated 2026-11-01
Also called: Medical oxygen, O2
Mechanism of action
Raising the inspired oxygen fraction raises its partial pressure in the alveolus and arterial blood; haemoglobin becomes more saturated and carries more oxygen to the tissues, where mitochondrial cytochrome c oxidase uses it as the final electron acceptor to make ATP. In a hyperbaric chamber much more oxygen dissolves in plasma and carbon monoxide leaves haemoglobin faster.
- Alveolar oxygen partial pressure rises
- Haemoglobin saturation increases
- More oxygen reaches the tissues
- Mitochondria use it to make ATP
Pharmacokinetics
- Absorption
- By diffusion from the alveolus; depends on ventilation and gas exchange.
- Distribution
- Bound to haemoglobin, with a small part dissolved in plasma (much more under hyperbaric conditions).
- Elimination
- Consumed in metabolism and eliminated as CO2 and water.
Indications
- Hypoxaemia in COPD, including long-term home oxygen Chronic obstructive pulmonary disease (COPD) →
- Acute hypoxaemia from pneumonia, severe asthma attacks or other causes of respiratory failure Acute respiratory failure (hypoxaemic and hypercapnic) →
- Carbon monoxide poisoning, including hyperbaric therapy Carbon monoxide poisoning →
- Decompression sickness and gas embolism (hyperbaric therapy) Decompression sickness and diving injuries →
- Anaesthesia and resuscitation, and when nitrous oxide is stopped
Adverse effects
Common
- Dry or bloody nose
- Irritation of mucosa and eyes with dry gas
- Tiredness and morning headache (home oxygen)
Contraindications
- No absolute contraindications when there is hypoxaemia; excess without need is avoided
Key interactions
- Opioids, sedatives and anaesthetics
- They depress ventilation: on oxygen, saturation can look fine while CO2 rises, so breathing is watched too.
What is monitored
- Pulse oximetry saturation against a defined target
- Arterial blood gases when hypercapnia is a risk
- Respiratory rate and level of consciousness
- In preterm infants: tight saturation control and retinopathy screening
Administration and safety
- Prescribed with a device (cannula, mask) and a saturation target; adjusted to the response.
- Humidify oxygen when given for long periods.
- Use only equipment cleaned for oxygen service and regulators designed for oxygen.
- Cylinders secured and upright, away from flames and heat sources.
Nursing care
- Assess saturation, respiratory rate, work of breathing and mental state.
- Teach the patient and family not to smoke or light flames or flammable materials nearby.
- Check the skin under the cannula or mask (ears, nose) and the humidification.
- Report if saturation does not reach the target or drowsiness appears.
Pregnancy and breastfeeding
Used when there is maternal hypoxaemia, which also puts the fetus at risk.
Test yourself
Think of the answer, then tap the question to see it.
Which eye complication is linked to excess oxygen in the preterm newborn?
Retinopathy of prematurity, from abnormal vascularisation of the immature retina.
What is absorption atelectasis?
The collapse of poorly ventilated alveoli when concentrated oxygen replaces nitrogen, which is poorly soluble and keeps alveoli open; the oxygen is absorbed and the alveolus empties.
Why does hyperbaric oxygen help in carbon monoxide poisoning?
It greatly increases the oxygen dissolved in plasma and speeds the release of CO from haemoglobin.
Related drugs
Related conditions
- Chronic obstructive pulmonary disease (COPD)
- Acute respiratory failure (hypoxaemic and hypercapnic)
- Carbon monoxide poisoning
- Decompression sickness and diving injuries
← Back to the class: Medical gases
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Oxygen Therapy | Hyperbaric Oxygen Therapy | MedlinePlus (MedlinePlus (U.S. National Library of Medicine), 2026); DailyMed - OXYGEN gas (DailyMed (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 24 (McGraw Hill, 2023); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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