Why this matters: Oxygen is an essential medicine for hypoxaemia, respiratory distress, shock, trauma, cardiac arrest and many acute illnesses. Too little oxygen injures organs; too much oxygen can also harm selected patients. EMTs must assess the patient, select a delivery device, titrate to a target, monitor response and keep oxygen available during every transfer.
Safety notice: Follow local protocols and patient-specific targets. Oxygen does not replace airway opening, ventilation, circulation support or treatment of the cause. In an emergency with severe hypoxaemia or arrest, give high-concentration oxygen while preparing definitive care, then titrate when reliable monitoring is available.
Learning outcomes
- Recognise clinical and oximetry signs of hypoxaemia and respiratory failure.
- Use pulse oximetry correctly, understand limitations and confirm with ABG when needed.
- Select nasal cannula, masks, BVM, HFNC, CPAP or NIV appropriately.
- Set and reassess target saturation for general patients, hypercapnic-risk patients and children/neonates under local guidance.
- Handle oxygen cylinders, concentrators, tubing, humidification and fire risks safely.
- Document oxygen device, flow/FiO2, saturation, response and escalation.
1. Oxygen physiology in simple terms
Oxygen enters the lungs, crosses the alveoli, binds haemoglobin and is delivered by the circulation to tissues. A normal SpO2 does not guarantee adequate oxygen delivery if haemoglobin is low, circulation is poor or carbon monoxide occupies haemoglobin. Conversely, a patient may have severe respiratory distress before SpO2 falls. Assess the whole patient: work of breathing, mental state, skin, pulse, BP, lactate and urine output.
| Term | Meaning | EMT relevance |
|---|---|---|
| Hypoxaemia | Low oxygen in arterial blood. | Detected by SpO2/PaO2 and clinical signs; treat promptly. |
| Hypoxia | Inadequate oxygen at tissue level. | May occur with anaemia, shock or CO poisoning even when SpO2 looks normal. |
| FiO2 | Fraction of inspired oxygen delivered. | Room air is about 0.21; masks/devices deliver variable FiO2 depending on flow and seal. |
| SpO2 | Pulse-oximeter estimate of haemoglobin saturation. | Trend with waveform/perfusion; confirm unexpected values. |
| PaO2 | Dissolved oxygen measured on ABG. | Interpreted with FiO2, altitude, age, haemoglobin and clinical condition. |
2. Assessing the patient before oxygen
- Ensure scene safety and use PPE; identify smoke/chemical exposure and fire risk.
- Check airway patency, breathing rate/effort, chest rise, lung sounds, colour, mental state and ability to speak.
- Measure SpO2 with a reliable probe and waveform; check pulse, BP, temperature, glucose and ECG when indicated.
- Ask about COPD/hypercapnic respiratory failure, home oxygen, asthma, heart/lung disease, anaemia, pregnancy and recent sedation/opioids.
- Identify the cause: pneumonia, asthma/COPD, pulmonary oedema, PE, shock, sepsis, trauma, drowning, poisoning or cardiac arrest.
- Choose device and target, start oxygen, reassess within minutes and escalate if work of breathing or mental state worsens.
3. Recognising hypoxaemia and respiratory failure
| Finding | Possible meaning | Action |
|---|---|---|
| Low SpO2 with distress | Hypoxaemic respiratory failure. | Oxygen/ventilation, ABCDE, treat cause and seek advanced help. |
| Normal SpO2 but exhaustion | Impending ventilatory failure or severe work of breathing. | Check ETCO2/ABG, prepare BVM/NIV/advanced airway. |
| Cyanosis | Severe desaturation or dyshemoglobinaemia; can be absent in anaemia. | High-concentration oxygen, verify probe/ABG and urgent review. |
| Confusion/agitation | Hypoxia, hypercapnia, shock, glucose/toxin or sepsis. | ABCDE and glucose; do not label psychiatric without medical screen. |
| Silent chest/poor air entry | Critical asthma, obstruction, pneumothorax or fatigue. | Emergency escalation; ventilation may be needed. |
4. Oxygen delivery devices
| Device | Use | Practical checks |
|---|---|---|
| Nasal cannula | Low-flow support for a spontaneously breathing patient with mild hypoxaemia. | Correct prongs, comfort, humidification if prolonged, flow and response. |
| Simple face mask | Moderate oxygen requirement when a tight seal is possible. | Use sufficient flow to prevent rebreathing; remove for eating/communication with monitoring. |
| Venturi mask | Controlled FiO2, useful when a precise target is required. | Use the correct colour/flow combination; do not obstruct entrainment ports. |
| Non-rebreather mask | High-concentration oxygen for severe hypoxaemia, shock or pre-oxygenation. | Inflate reservoir before application; check valves, seal and cylinder supply. |
| Bag-valve-mask | Apnoea, agonal breathing or inadequate ventilation. | Requires airway opening, mask seal, oxygen/reservoir and controlled breaths. |
| High-flow nasal oxygen | Heated humidified high flow for selected hypoxaemic patients. | Needs reliable oxygen source and monitoring; does not replace a failing airway. |
| CPAP/NIV | Selected conscious patients with pulmonary oedema, COPD or respiratory failure. | Contraindicated with vomiting, severe agitation, shock or inability to protect airway. |
| Tracheostomy/ventilator circuit | Patients with established airway and ventilatory support. | Check tube patency, humidification, cuff, suction, spare tube and backup BVM. |
5. Target saturation and titration
| Patient context | Typical target approach | Why individualise? |
|---|---|---|
| Most acutely ill adults | Often 94–98% once reliable readings are available. | Avoid persistent hypoxaemia and unnecessary hyperoxia; follow local protocol. |
| Risk of hypercapnic respiratory failure | Often 88–92% pending ABG/clinician direction. | Excess oxygen can worsen CO2 retention in susceptible COPD/neuromuscular patients; never withhold emergency oxygen from a critically hypoxic patient. |
| Cardiac arrest/peri-arrest | Use high-concentration oxygen during resuscitation; titrate after ROSC and reliable measurement. | Oxygenation and ventilation must be continuously monitored. |
| Children/neonates | Age-, condition- and gestation-specific targets; use paediatric/neonatal protocol. | Both hypoxia and unregulated hyperoxia can cause harm. |
| Carbon monoxide suspicion | Give high-concentration oxygen and urgent specialist assessment. | SpO2 can be falsely reassuring; co-oximetry/ABG may be needed. |
6. Pulse oximetry technique
- Choose the correct probe and site; warm cold extremities and remove nail products where possible.
- Check the plethysmography waveform and compare displayed pulse with palpated pulse.
- Keep the hand still, shield from strong light and recheck after oxygen/device changes.
- Look for poor perfusion, motion, dysrhythmia, skin pigmentation/probe issues and venous pulsation.
- Do not rely on SpO2 alone in carbon monoxide exposure, shock, severe anaemia or an unexpected clinical picture.
Oxygen is titrated to the patient, not the monitor. A rising SpO2 with worsening fatigue, confusion or CO2 retention is not a successful outcome—reassess ventilation and the underlying cause.
7. Oxygen in common emergencies
| Emergency | Oxygen/ventilation priorities |
|---|---|
| Asthma/COPD | Titrate to target, bronchodilator protocol, assess fatigue/CO2 and escalate NIV/intubation if failing. |
| Pulmonary oedema | Upright position, oxygen if hypoxaemic, CPAP/NIV when indicated and treat cardiac cause. |
| Sepsis/shock | Oxygen for hypoxaemia, support perfusion, lactate/ABG and rapid infection management. |
| Trauma/haemorrhage | Airway/oxygenation, bleeding control, ventilation and blood/fluid pathway; prevent hypothermia. |
| Drowning | Ventilation is crucial; oxygen, BVM, airway protection, hypothermia management and observation. |
| Carbon monoxide | High-concentration oxygen, remove from source, monitor ECG/neurology and arrange co-oximetry/specialist care. |
| Cardiac arrest | 100%/maximum available oxygen during CPR, effective BVM/advanced airway and capnography, then titrate after ROSC. |
8. Cylinder, concentrator and fire safety
- Oxygen supports combustion: no smoking, flames, sparks, petroleum products or oil/grease near cylinders, regulators or masks.
- Secure cylinders upright with three points of contact; separate full and empty cylinders and check pressure before leaving.
- Open valves slowly, use the correct regulator and never force a connection. Listen for leaks.
- Keep cylinders away from heat, sunlight, impact and vehicle movement; use approved holders.
- Check concentrator power, oxygen concentration/flow, filters, alarms and backup cylinder before relying on it.
- Do not store oxygen in an unventilated ambulance compartment; follow facility fire and transport policy.
9. Humidification and airway care
Dry high-flow oxygen can irritate mucosa, thicken secretions and worsen discomfort. Use humidification when indicated by flow, duration, tracheostomy or local policy. Keep water traps below the patient, prevent condensate entering the airway, use sterile/clean water as required and change circuits only according to protocol.
10. Monitoring after oxygen starts
| Time point | What to record |
|---|---|
| Before | RR/effort, SpO2 waveform, pulse/BP, mental state, oxygen device/flow, lung signs, glucose and cause. |
| After initiation | SpO2 response, work of breathing, ability to speak, colour, comfort, pulse/BP and device function. |
| After change | New device/flow/FiO2, time, target, response and escalation decision. |
| During transfer | Cylinder reserve, battery, tubing, mask seal, continuous SpO2/ECG and backup BVM/oxygen. |
| If deterioration | ABCDE, ABG/ETCO2 when available, suction, BVM, chest assessment and urgent senior review. |
11. Clinical scenarios
Scenario 1 — COPD exacerbation: A patient is drowsy with RR 30 and SpO2 82% on room air. Give emergency oxygen, titrate toward the locally specified target, obtain ABG/ETCO2 and prepare NIV/airway support; do not withhold oxygen out of fear of CO2 retention.
Scenario 2 — Pulmonary oedema: A breathless patient is sitting upright, coughing pink froth and has low SpO2. Apply appropriate oxygen, consider CPAP/NIV if conscious and haemodynamically suitable, monitor BP/ECG and escalate.
Scenario 3 — Normal SpO2 in CO exposure: Several family members have headache and confusion after a charcoal stove was used indoors. Give high-concentration oxygen, move to fresh air, check for fire/scene safety and arrange urgent specialist assessment; pulse oximetry may be misleading.
Scenario 4 — Cylinder failure: During transfer the reservoir bag collapses and SpO2 falls. Check cylinder/regulator/tubing, switch to backup source, use BVM if ventilation is inadequate and report equipment failure.
Scenario 5 — Hypoxic child: A child with pneumonia has increased work of breathing and low SpO2. Use the correct paediatric probe/device, target the age/condition-specific range, reassess frequently and escalate for CPAP/ventilation if tiring.
12. Oxygen prescription and handover
- Indication and suspected cause of hypoxaemia.
- Target saturation/range and whether hypercapnic-risk guidance applies.
- Device, flow or FiO2, humidification and time started/changed.
- Pre/post SpO2, waveform quality, RR/work of breathing, mental state, BP/ECG and ABG/ETCO2 if available.
- Response, complications, cylinder/concentrator reserve and escalation plan.
13. Revision questions
- Why can oxygen be both lifesaving and harmful?
- What are the limitations of pulse oximetry?
- Which patients may need a lower target range while awaiting ABG?
- Why must a non-rebreather reservoir be inflated before application?
- When is NIV unsafe?
- What fire-safety rules apply to oxygen cylinders?
- Why is high-flow oxygen appropriate immediately after cardiac arrest but titrated after ROSC?
- What signs show that a patient needs ventilation rather than oxygen alone?
- What details should appear in an oxygen handover?
- How can a normal SpO2 be misleading in carbon monoxide exposure?
14. Key take-home points
- Assess airway, breathing, circulation and cause before choosing an oxygen device.
- Use reliable pulse oximetry and titrate oxygen to an appropriate target; reassess work of breathing and mental state.
- Oxygen does not correct hypoventilation—use BVM/NIV/ventilation when CO2 clearance or airway protection fails.
- Protect cylinders and concentrators from fire, impact, leaks and empty reserves.
- Document device, flow/FiO2, target and response during every handover and transfer.
Selected authoritative resources
- WHO oxygen therapy for children.
- Resuscitation Council UK ABCDE approach.
- WHO oxygen-cylinder safety.
- WHO medical oxygen standards and devices.
For EMT practice: Give oxygen early when the patient needs it, measure its effect, titrate safely and always keep a ventilation rescue plan ready.