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Someone is severely breathless, blue around the lips or fingertips, confused, drowsy or unrousable, or their oxygen level drops suddenly and stays low.
Do not wait to "see if it improves." If you use home oxygen, keep it running while you call. This page is general information, not a substitute for emergency care.
The two jobs of breathing
Every breath does two jobs, and they can fail independently:
- Oxygenation — moving oxygen from the air into the blood. When this fails, blood oxygen falls (hypoxaemia). This is what a pulse oximeter measures.
- Ventilation — moving air in and out to clear carbon dioxide (CO₂). When this fails, CO₂ rises in the blood (hypercapnia). A pulse oximeter does not measure this.
Understanding the difference matters, because someone can have a "normal" oxygen reading while carbon dioxide is quietly climbing — and, in some people, too much oxygen can actually make the CO₂ problem worse (see below).
What is oxygen saturation (SpO₂)?
Oxygen saturation is the percentage of the haemoglobin in your red blood cells that is carrying oxygen. A pulse oximeter — the clip on your finger — estimates this and shows it as SpO₂, along with your pulse rate.1
| Reading | What it usually means |
|---|---|
| 95–100% | Normal for most healthy adults at sea level. |
| 92–96% | A common target range for many people who are unwell — your team may set your own target. |
| 88–92% | The target range set for some people with COPD or other conditions who are at risk of carbon-dioxide retention. For them, a higher number is not safer. |
| Below your target | Needs attention — follow your action plan and seek advice; a sudden or large drop is an emergency. |
These are general figures. Your own safe range is set by your treating team and written into your plan — always follow that rather than a generic number.
Measuring it well at home
Pulse oximeters are useful but easily fooled. For a reliable reading: warm your hands, sit still and rest for a minute, remove nail polish or false nails, and let the number settle. Readings can be falsely low with cold hands, poor circulation, movement or a weak pulse signal, and can be falsely reassuring in some situations. Trust how the person looks and feels as much as the number.
When breathing fails: the two types
Doctors describe two patterns of respiratory failure, and physiotherapy has a role in both:
| Type 1 (low oxygen) | Type 2 (low oxygen + high CO₂) | |
|---|---|---|
| Problem | Oxygenation fails | Ventilation fails — CO₂ builds up |
| Typical causes | Pneumonia, pulmonary oedema, PE, ARDS | Severe COPD, chest-wall or neuromuscular weakness, over-sedation, obesity hypoventilation |
| How it feels | Breathless, fast breathing, sometimes blue lips | Headache (worse in the morning), drowsiness, flushed warm skin, tremor/flap, confusion |
| Support that helps | Controlled oxygen; treat the cause | Non-invasive ventilation (BiPAP), careful oxygen, airway clearance |
Signs carbon dioxide may be rising (hypercapnia)
Because you cannot see CO₂ on a finger monitor, learn the warning signs: a morning headache, unusual daytime sleepiness or difficulty staying awake, warm flushed skin, a fine tremor or "flapping" of the outstretched hands, and confusion. If these appear — especially in someone with COPD or on home oxygen — seek medical advice promptly; if they are drowsy or hard to rouse, call an ambulance.
Why more oxygen isn't always better
For most people, if oxygen is low, giving oxygen helps. But a minority — particularly some people with advanced COPD — rely on a lower oxygen level to keep their breathing drive, and giving too much oxygen can let carbon dioxide climb dangerously. This is why these patients are given a target range (often 88–92%) and why you should never turn your home oxygen up on your own. Set it to the flow you were prescribed and call your team if it isn't enough.2
How physiotherapy & breathing support help
Cardiorespiratory physiotherapy improves both oxygenation and ventilation without always needing more oxygen:3
- Positioning — sitting upright or leaning forward, or lying on one side, can noticeably improve oxygen levels.
- Breathing retraining & pacing — slower, controlled breathing improves the efficiency of each breath. See Breathing Retraining.
- Airway clearance — clearing retained secretions opens up lung units so oxygen can get in. See Principles of Airway Clearance.
- Home oxygen — used safely, at the prescribed flow. See Oxygen in the Home.
- Non-invasive ventilation (CPAP/BiPAP) — supports ventilation and lowers carbon dioxide. See NIV (CPAP & BiPAP).
Cardiorespiratory physiotherapists assess every patient against six core problems: reduced lung volume, sputum retention, increased work of breathing, impaired gas exchange, reduced exercise tolerance and pain. Low oxygen and rising carbon dioxide are the face of impaired gas exchange — and often overlap with the others. See Cardiorespiratory Physiotherapy, Breathlessness and Decreased Exercise Tolerance.
References & evidence base
- O’Driscoll BR, Howard LS, Earis J, et al. BTS guideline for oxygen use in adults in healthcare and emergency settings. Thorax 2017;72(Suppl 1):ii1–ii90.
- Beasley R, Chien J, Douglas J, et al. Thoracic Society of Australia and New Zealand oxygen guidelines for acute oxygen use in adults. Respirology 2015;20(8):1182–1191.
- Global Initiative for Chronic Obstructive Lung Disease. Global strategy for the diagnosis, management and prevention of COPD: 2026 report. GOLD; 2026. Available at: goldcopd.org
References are numbered in citation order (Vancouver/BMJ style) and were current at the time of writing. Guidelines are living documents — verify against the latest version before clinical use.
Corrections: If something on this page is wrong, out of date or unclear, we want to know. Email reception@inspireclinic.au with the page name and what you believe is incorrect. Substantive corrections are made promptly, and the guide’s version and last-updated date are changed to reflect it.