RESPIRATORY CARE · FREE NURSING NOTES

Oxygen Therapy

Methods, flow rates, precautions, nursing care and 12 explained MCQs.

25 October 2026 · Adult acute care, with separate paediatric considerations

1. Definition & indications

Oxygen therapy supplies supplemental oxygen to raise inspired oxygen concentration and correct hypoxaemia. It supports oxygen delivery while the cause is treated; it does not replace airway management, ventilation or circulation.

Indications: hypoxaemia associated with respiratory illness, shock or critical illness; indicated peri-procedural support; and special indications such as carbon monoxide poisoning. Routine oxygen is not required for every breathless patient or uncomplicated myocardial infarction/stroke with normal oxygenation.

Prescribe a target. BTS adult guidance commonly uses SpO₂ 94–98% for most acutely ill adults and 88–92% for those at risk of hypercapnic respiratory failure pending blood gases. Other guidance, including TSANZ, uses 92–96% for most adults. Follow the individual prescription and local protocol. [1,2]

Contraindications & precautions

Do not withhold oxygen needed for life-threatening hypoxaemia. Avoid unnecessary hyperoxia. COPD is not an absolute contraindication: use controlled oxygen and reassessment. Paraquat exposure and prior bleomycin treatment require specialist advice about oxygen exposure.

L/min ≠ FiO₂: flow is gas volume per minute; FiO₂ is oxygen concentration (room air ≈21%). Low-flow concentrations are approximate. A reservoir mask delivers high concentration but does not necessarily meet all inspiratory flow demand. [3,4]

2. Delivery methods & amounts

Typical adult ranges below are revision guides. Actual delivery depends on equipment, fit and breathing. Always check the manufacturer instructions and response. [1–5]

Nasal cannula

1–6 L/min · approximately 24–44% FiO₂

Indications: Mild hypoxaemia; allows eating and speech.

Contraindications / limitations: Blocked/injured nose or insufficient oxygenation requires another device.

Side effects: Dryness, epistaxis, pressure injury at ears/nares.

Device care: Check prong placement and skin. FiO₂ changes with breathing pattern.

Simple face mask

5–10 L/min · approximately 35–60% FiO₂

Indications: Moderate oxygen requirement in a spontaneously breathing patient.

Contraindications / limitations: Do not run below 5 L/min: CO₂ may accumulate. Avoid in vomiting or unprotected airway.

Side effects: Claustrophobia, skin pressure, CO₂ rebreathing at inadequate flow.

Device care: Keep exhalation ports open; arrange prescribed alternative support for meals.

Partial-rebreather mask

Usually 6–10 L/min · approximately 40–70% FiO₂; device dependent

Indications: Selected reservoir-oxygen use according to local practice.

Contraindications / limitations: Not precise FiO₂; unsuitable for apnoea or inability to protect airway.

Side effects: Bag collapse, variable delivery, CO₂ rebreathing and pressure injury.

Device care: Inflate reservoir first; adjust flow to prevent collapse during inspiration. Follow device instructions.

Non-rebreather reservoir mask

10–15 L/min; commonly 15 L/min in emergencies · approximately 60–90% FiO₂

Indications: Severe hypoxaemia while urgent assessment proceeds.

Contraindications / limitations: Does not ventilate an apnoeic patient. Poor seal or faulty valves reduces delivery.

Side effects: Supply failure, reservoir collapse, pressure injury and hyperoxia.

Device care: Pre-inflate reservoir; check valves and oxygen supply. Bag must not collapse on inspiration. Do not assume 100% FiO₂.

Venturi mask

Usually 24–60% FiO₂ · set flow printed on the selected adapter

Indications: Controlled oxygen when a specified concentration is needed.

Contraindications / limitations: Do not obstruct entrainment ports or choose an arbitrary adapter/flow pairing.

Side effects: Discomfort, skin pressure; incorrect concentration if air ports are blocked.

Device care: Read adapter instructions; colour codes vary. Ensure total gas flow meets inspiratory demand.

Heated humidified HFNC

Adult systems commonly 20–60 L/min · FiO₂ 21–100%

Indications: Selected acute hypoxaemic respiratory failure with close monitoring.

Contraindications / limitations: Cannot replace airway protection or delay intubation; major nasal/facial injury may prevent fitting.

Side effects: Discomfort, nasal injury, heat intolerance, possible air leak; delayed escalation.

Device care: Set flow and FiO₂ separately. Check correct-size prongs, heated humidifier, alarms and respiratory effort.

Tracheostomy collar / T-piece

FiO₂ set by blender/entrainment system; flow must meet demand

Indications: Spontaneously breathing patient with an artificial airway.

Contraindications / limitations: No universal L/min-to-FiO₂ conversion. Blocked tube or apnoea needs airway/ventilation management.

Side effects: Dry secretions and obstruction, contamination, condensate aspiration.

Device care: Deliver to the stoma; provide appropriate humidification, assess tube patency and drain water away from patient.

Face tent

Variable FiO₂; commonly humidified flow ≥10 L/min, equipment dependent

Indications: Selected mask intolerance or facial injury when a loose interface is suitable.

Contraindications / limitations: Not reliable for precise concentration or unstable severe hypoxaemia.

Side effects: Variable delivery, wet skin and contamination.

Device care: Check position and clinical response; follow manufacturer setup.

CPAP, bilevel NIV & invasive ventilation

These provide respiratory support rather than a single fixed oxygen flow. FiO₂ and airway pressures are separately prescribed. NIV benefits selected COPD exacerbations with respiratory acidosis and cardiogenic pulmonary oedema. Arrest, inability to protect the airway, vomiting, major facial trauma or severe instability may require invasive airway management. Watch for mask injury, air leak, gastric distension, aspiration, hypotension and barotrauma. [6]

Infants, children, oxygen hoods & tents

Adult settings must not be applied automatically to children. Nasal-prong settings depend on age, size and equipment. Hoods require adequate fresh-gas flow to clear CO₂ and measurement of concentration near the infant; one flow is not safe for every hood. WHO discourages routine head boxes/tents where efficient alternatives are available. Premature infants need neonatal targets to reduce hyperoxia-related injury. Nasal/nasopharyngeal catheters need trained insertion and local protocols. [7]

Escalate immediately: apnoea, exhaustion, deteriorating consciousness, shock or persistent desaturation may require ventilation. Repeated mask changes must not delay emergency care.

3. Nursing care: before, during & after

Before

Identify patient, explain treatment and perform hand hygiene.
Assess airway, respiratory effort/rate, SpO₂, pulse, blood pressure, consciousness and skin.
Check target, device and initial setting; identify hypercapnia risk. Start emergency oxygen according to protocol and document promptly.
Check source, flowmeter, connections, cylinder reserve and backup for transport.
Position upright when appropriate; prepare the correct interface and prescribed humidification.

During

Fit the interface and confirm gas delivery.
Reassess after starting or changing support; continuously monitor unstable patients.
Check skin, mouth and nose; provide pressure protection and oral care.
Monitor ventilation as well as saturation. Obtain indicated blood gases; drowsiness needs urgent review.
Check reservoirs, ports, tubing and humidifiers. Use approved water and infection-control practice.
Record device, flow/FiO₂, target, observations, response and escalation.

After / weaning

Reduce support according to the prescribed plan once stable and reassess each change. Do not abruptly remove needed oxygen solely because CO₂ retention is suspected. After stopping, assess room-air saturation and symptoms; BTS advises checks around 5 minutes and again at 1 hour if stable. Restart the lowest effective support and seek review if below target. Clean/dispose of equipment, inspect skin and document response. [1]

Fire safety: no smoking, flames, sparks or oil/grease. Secure cylinders and use approved water-based products. Oxygen supports combustion; it is not itself flammable.

4. General adverse effects

Hyperoxia: excessive exposure can cause lung injury and absorption atelectasis. Use the lowest concentration meeting the target.
Hypercapnia: susceptible patients may retain CO₂; assess ventilation and blood gases.
Dryness, bleeding and pressure injury: assess contact points and provide skin/mouth care and suitable humidification.
Infection: prevent contaminated equipment and humidifiers.
Fire or interrupted supply: enforce precautions and verify oxygen availability during transfers.

SpO₂ alone does not measure CO₂ or exclude carbon monoxide poisoning. Use clinical assessment and indicated blood gases/co-oximetry. [1,4,5]

5. Practise: 12 original MCQs

Choose an option to reveal the answer and rationale.

1. A simple mask is running at 2 L/min. Priority?

2. Best device for a specified 28% concentration?

3. NRB reservoir collapses during inspiration. Action?

4. Usual initial target for hypercapnia risk pending blood gases?

5. An apnoeic patient has an NRB. What is missing?

6. HFNC requires:

7. Tracheostomy with thick secretions: check first?

8. Appropriate lubricant near oxygen?

9. All breathlessness with normal oxygenation requires oxygen.

10. Drowsiness after increased oxygen needs:

11. Standard cannula FiO₂ is:

12. After oxygen discontinuation:

Sources & scope

Educational revision; follow the individual prescription, local policy and equipment instructions. Adult and paediatric settings are not interchangeable. References checked 25 October 2026.

Original revision text and questions. No third-party photographs or textbook diagrams reproduced.