Asthma vs COPD: Differences That Matter in the Field
How asthma and COPD differ in cause, reversibility and baseline, why the oxygen target changes for a COPD patient, the signs of a life-threatening attack, and where CPAP fits.
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Asthma and chronic obstructive pulmonary disease (COPD) both narrow the airways and both make a patient wheeze and fight to get air out. In an acute attack they can look almost identical, and the first treatments are much the same. The differences matter most for two things: what you expect the patient's normal to be, and how much oxygen you give.
Side by side
| Feature | Asthma | COPD |
|---|---|---|
| Usual age at onset | Often childhood or young adulthood, but can start at any age | Usually over 40 |
| Main cause | Airway inflammation set off by triggers | Long-term smoking or other inhaled exposure |
| Triggers | Allergens, exercise, cold air, infections, smoke, stress | Infections and pollution most often set off a flare |
| Reversibility | Airway narrowing largely reverses with treatment | Only partly reverses; some damage is permanent |
| Between attacks | Often normal breathing | Ongoing breathlessness, cough and sputum are common |
| Home equipment | Inhalers, sometimes a nebulizer | Inhalers, often home oxygen or a home nebulizer |
Many patients have features of both, especially older patients with long-standing asthma or a smoker who also has asthma. You do not need to settle the diagnosis to treat the attack. You do need to know the patient's history, because it changes the oxygen target and what counts as normal for them.
Oxygen: the difference that matters most
In some patients with COPD, high-flow oxygen raises the CO2, mainly by worsening the mismatch between ventilation and blood flow in the lungs, and can make them drowsy. Giving them high-flow oxygen to a saturation of 100 percent can raise their CO2 further and make them drowsy. The British Thoracic Society oxygen guideline therefore sets a target saturation of 88 to 92 percent for patients at risk of CO2 retention, and 94 to 98 percent for most other adults, including most patients with asthma.
Recognizing a life-threatening attack
In either condition, the patient who is getting worse is often the one who looks quieter. Watch for:
- A silent chest: little or no wheeze because almost no air is moving. It is a sign of severe obstruction, not improvement.
- Unable to speak in full sentences, or only a word or two at a time.
- Exhaustion, with a respiratory rate that is falling while the patient still looks unwell.
- Confusion, drowsiness or agitation, which may mean rising CO2 or falling oxygen.
- Low oxygen saturation despite treatment, cyanosis, or a slowing heart rate.
A patient with these signs needs immediate, aggressive treatment as your protocol directs, early help and early notification of the receiving facility.
Ventilation support
Many protocols use CPAP for a COPD exacerbation in a patient who is alert enough to protect the airway, because it reduces the work of breathing and can avoid intubation. Its use in severe asthma is more cautious or not included in some protocols, because trapped air in an asthmatic chest raises the risk of air leak and of low blood pressure under positive pressure. Follow your protocol for both.
If you have to assist ventilation with a bag in either condition, give the lungs time to empty. A slow rate with a long pause for exhalation lets trapped air out; bagging fast stacks breaths on top of each other and can drop the blood pressure.
Work out how long an oxygen cylinder will last at your flow rate
The short version
- Asthma and COPD both narrow the airways; an acute attack of either looks similar and is treated similarly.
- Asthma is usually reversible and the patient is often normal between attacks; COPD is partly permanent and the patient's baseline is often breathless.
- Oxygen target: 88 to 92 percent for a COPD patient at risk of CO2 retention, 94 to 98 percent for most others. Never withhold oxygen from a hypoxic patient.
- A silent chest, an inability to speak and a falling respiratory rate in a tiring patient are signs of a life-threatening attack.
- CPAP and how you ventilate are protocol decisions; if you bag, go slowly and let the air out.