Synopsis
Prescribe oxygen as a titrated treatment with an explicit saturation target, appropriate device and reassessment plan, including safe management of patients at risk of hypercapnic respiratory failure.
- Oxygen treats hypoxaemia, not breathlessness. Prescribe a target saturation, device/flow and monitoring plan rather than a fixed dose with no endpoint.
- For most acutely ill adults, target SpO2 94–98%. For known COPD or another risk of hypercapnic respiratory failure, target 88–92% pending blood gases.
- Risk factors for hypercapnia include prior hypercapnic failure, severe COPD, morbid obesity, neuromuscular disease, chest-wall deformity, cystic fibrosis and fixed airflow obstruction in bronchiectasis.
- Critical illness or SpO2 below about 85% usually starts with a reservoir mask at 15 L/min while help and blood gases are obtained; titrate down promptly once reliable data are available.
- A 24% or 28% Venturi mask provides controlled FiO2 and is often the initial device in COPD/hypercapnia risk; use the manufacturer-marked minimum flow, not a guessed universal flow.
- Repeat blood gases after 30–60 minutes in patients at risk of hypercapnic failure, even if the first PaCO2 is normal, and sooner if consciousness or breathing worsens.
- If PaCO2 rises or pH falls, reduce oxygen to the minimum that maintains 88–92% and assess for NIV; never stop oxygen abruptly.
- A simple face mask must run at least 5 L/min to avoid CO2 rebreathing; nasal cannulae provide variable FiO2 and are useful for lower, titratable requirements.
- Carbon monoxide poisoning is an exception: pulse oximetry is unreliable; give 100% oxygen via reservoir mask irrespective of the apparent SpO2 while measuring co-oximetry and obtaining toxicology advice.
- Every transfer needs enough oxygen supply, a functioning delivery system, continued monitoring and a handover of target, device and remaining cylinder time.