Acute breathlessness
Oxygen to target, sit them up, then work out which of the common causes you are dealing with. A quiet, tired patient who was breathless is about to arrest.
A 64-year-old woman is brought in gasping. She sits bolt upright, RR 34, SpO₂ 82% on air, pulse 118, BP 176/98. Crackles to both mid-zones. Her son says she has "sugar and BP" and has been sleeping on three pillows for a week.
What do you do in the first 15 minutes?
- Sit up, oxygen to target94–98% for most. 88–92% if at risk of CO₂ retention (COPD, obesity, neuromuscular).
- Look for the peri-arrest signsSilent chest, exhaustion, drowsy, cyanosed, SpO₂ falling despite oxygen.
- Listen and decide the patternWheeze, crackles, one side quiet, or a clear chest.
- Blood gas, ECG, chest X-rayPortable X-ray if too unwell to move.
- Start treatment for the likely causeDo not wait for every result.
- Reassess in 15–30 minutesRR, SpO₂, work of breathing, gas.
- Senior earlyEspecially if you are thinking NIV, ICU or a chest drain.
- SpO₂ below target despite oxygen
- Drowsy, exhausted or a silent chest
- pH below 7.35 with a high CO₂
- BP below 90 systolic
- Suspected tension pneumothorax or massive PE
- Tension pneumothorax
- Anaphylaxis (rash, swelling, recent drug or food)
- Massive PE (clear chest, low BP)
- DKA or sepsis breathing (acidosis)
- Upper airway obstruction (stridor)
- Cardiac tamponade
| Oxygen target, most adults | SpO₂ 94–98% |
| Oxygen target, CO₂ retainers | SpO₂ 88–92% |
| Respiratory rate | Above 30 or below 8 is dangerous |
| Type 1 failure | PaO₂ below 60 mmHg (8 kPa), PaCO₂ normal or low |
| Type 2 failure | PaCO₂ above 45 mmHg (6 kPa) |
| Acidotic type 2 | pH below 7.35 with high CO₂: senior and NIV decision |
| Tension pneumothorax | Decompress before the X-ray |
Check every dose against a current drug reference and your hospital protocol.
On this page
Give oxygen, but give it to a target
Reservoir mask at 15 L/min for anyone critically ill. Then titrate to 94–98%, or to 88–92% if they may retain CO₂, and check a gas.
- Do not withhold oxygen from a hypoxic COPD patient. Give controlled oxygen (Venturi 24–28%) and check the gas in 30–60 minutes.
- Too much oxygen in a CO₂ retainer can push the CO₂ up and make them drowsy. Too little kills faster.
Find the pattern at the bedside
- Asthma
- COPD exacerbation
- Anaphylaxis (look for rash, swelling)
- Cardiac asthma (pulmonary oedema can wheeze)
- Pulmonary oedema (both bases, raised JVP, pink froth)
- Pneumonia (focal, fever, bronchial breathing)
- Interstitial lung disease (fine, chronic)
- Pneumothorax (hyper-resonant)
- Pleural effusion (stony dull)
- Collapse
- Pulmonary embolism
- Metabolic acidosis (DKA, sepsis, kidney failure, poisoning)
- Anaemia
- Anxiety (only after excluding the rest)
Read the blood gas in four steps
- OxygenPaO₂ below 60 mmHg (8 kPa) is respiratory failure. Always note the FiO₂.
- pHBelow 7.35 acidosis, above 7.45 alkalosis.
- CO₂Above 45 mmHg (6 kPa): type 2 failure. Acidotic type 2 needs a senior now.
- Bicarbonate and base excessLow in metabolic acidosis (DKA, sepsis, kidney failure). High bicarbonate means the high CO₂ is chronic.
| Pattern | Usual causes | What it means for you |
|---|---|---|
| Type 1: low O₂, normal or low CO₂ | Pneumonia, pulmonary oedema, PE, asthma early | Oxygen to 94–98%, treat the cause |
| Type 2: low O₂, high CO₂, normal pH | COPD (chronic) | Controlled oxygen, target 88–92% |
| Type 2 with acidosis | COPD exacerbation, tired asthmatic, obesity, opioids | Senior now: NIV or ICU |
| Low CO₂, low bicarbonate, acidosis | DKA, sepsis, kidney failure, poisoning | Breathing fast to blow off acid: treat the cause |
A normal or rising CO₂ in an asthmatic is not reassuring. It means they are tiring. Call for help.
First treatment by cause
| Cause | First steps | Guide |
|---|---|---|
| Asthma | Salbutamol back-to-back, ipratropium, steroid, magnesium if severe | Asthma |
| COPD | Nebulisers, steroid, antibiotic if purulent sputum, NIV if acidotic | COPD |
| Pulmonary oedema | Sit up, oxygen, IV furosemide, GTN if BP allows | Heart failure |
| Pneumonia | Oxygen, antibiotics within the hour if septic, CURB-65 | Pneumonia |
| Pulmonary embolism | Anticoagulate if no contraindication; thrombolysis if shocked | PE |
| Pneumothorax | Tension: decompress now. Otherwise size and symptoms decide | Pneumothorax |
| Anaphylaxis | IM adrenaline | Anaphylaxis |
Investigations
| Test | Why |
|---|---|
| Blood gas | Type of failure, pH, lactate, potassium |
| ECG | Ischaemia, arrhythmia, right heart strain |
| Chest X-ray | Oedema, consolidation, pneumothorax, effusion |
| CBC, urea, creatinine, electrolytes | Infection, anaemia, kidney function before diuretics |
| Troponin, BNP if available | Heart failure, ischaemia |
| Blood sugar, ketones | DKA breathing |
| D-dimer or CT pulmonary angiogram | Only after Wells score; see the PE guide |
| Bedside ultrasound | B-lines, effusion, pneumothorax, pericardial fluid, if you are trained |
Common mistakes
- Taking oxygen off a hypoxic COPD patient because "they retain CO₂".
- Calling a fast breather "anxious" before checking the gas and sugar.
- Giving furosemide to a breathless patient who is actually septic and dry.
- Sending a patient to the X-ray room alone while hypoxic.
- Missing the tiring asthmatic with a normal CO₂.
Frequently asked questions
What are the common causes of sudden shortness of breath?
In adults in the emergency: asthma, COPD exacerbation, pulmonary oedema, pneumonia, pulmonary embolism, pneumothorax and anaphylaxis. Metabolic acidosis (DKA, sepsis, kidney failure) also makes people breathe fast with a clear chest.
What is the first treatment for shortness of breath in the ER?
Sit the patient up and give oxygen to a target saturation (94–98%, or 88–92% if they retain CO₂), then treat the likely cause found from the chest examination, ECG, gas and X-ray.
What is the difference between type 1 and type 2 respiratory failure?
Type 1 is low oxygen with a normal or low CO₂. Type 2 is low oxygen with a high CO₂ (above 45 mmHg or 6 kPa), often from COPD or tiring.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A COPD patient has SpO₂ 80% on air. A nurse is worried oxygen will stop him breathing. What should you do?
Answer: Controlled oxygen, target 88–92%. Never leave a COPD patient hypoxic. Give controlled oxygen to 88–92% and check the gas in 30–60 minutes.
- 15 L/min non-rebreather and leave: Uncontrolled oxygen can raise CO₂.
- Give IV furosemide: Not the problem.
- Nasal cannula 6 L/min without monitoring: Uncontrolled.
- Withhold oxygen: Hypoxia kills faster.
2. A breathless patient has RR 32, a clear chest, SpO₂ 99% and glucose 26 mmol/L (468 mg/dL). What is the likely cause?
Answer: Ketoacidosis. Fast deep breathing with a clear chest and normal saturations suggests metabolic acidosis. Check ketones and a gas.
- Anxiety: Exclude causes first.
- Pneumonia: Clear chest.
- Pulmonary embolism: Possible, but high sugar points to DKA.
- Asthma: Chest is clear.
3. A blood gas shows pH 7.28, PaCO₂ 68 mmHg (9 kPa) and bicarbonate 34 mmol/L. What does it show?
Answer: Acute-on-chronic type 2 failure. High CO₂ with acidosis is acute respiratory acidosis; raised bicarbonate shows chronic compensation. This pattern needs senior review and possibly NIV.
- Respiratory alkalosis: pH is low.
- Metabolic acidosis: CO₂ is high and bicarbonate raised.
- Type 1 respiratory failure: CO₂ is high.
- Normal gas: Abnormal.
4. A 70-year-old has sudden severe breathlessness, frothy pink sputum, bilateral crackles and BP 180/100. SpO₂ is 85%. What is the initial treatment?
Answer: O₂, IV furosemide, nitrate. Acute cardiogenic pulmonary oedema: sit up, oxygen to SpO₂ > 94% (CPAP/NIV if hypoxic despite O₂), IV loop diuretic, IV nitrate if SBP > 110 (reduces preload/afterload), treat the cause (ACS, arrhythmia, hypertension, valve). Avoid routine morphine. Hypotensive patients (cardiogenic shock) need inotropes/vasopressors and specialist support.
- 500 mL IV saline bolus: A saline bolus worsens pulmonary oedema.
- IV metoprolol, oxygen: Beta-blockers are negatively inotropic in acute failure.
- Oral digoxin loading only: Digoxin alone is inadequate.
5. A 74-year-old man with known heart failure is acutely breathless, sitting upright, with crackles to both mid-zones. SpO₂ 89% on air, BP 156/92 mmHg. Chest X-ray shows bilateral alveolar oedema. What is the most important drug treatment?
Answer: IV furosemide. Acute pulmonary oedema with fluid overload is treated by sitting the patient up, giving oxygen to keep saturations at 94–98%, and IV loop diuretic (furosemide) to offload fluid; IV nitrates can help if BP is adequate. Opiates are no longer recommended routinely. Consider CPAP if hypoxia persists. Do not start a beta-blocker during acute decompensation.
- IV fluids 1 L over 1 hour: IV fluids worsen pulmonary oedema.
- Oral bisoprolol: Beta-blockers are not started during acute decompensation.
- IV morphine routinely: Routine morphine is no longer recommended — linked to worse outcomes.
6. Which fetal hormone is the most important stimulus for surfactant production and lung maturation?
Answer: Cortisol. Fetal cortisol rising in late pregnancy matures type II pneumocytes and increases surfactant. This is why steroids (betamethasone or dexamethasone) are given before expected preterm birth. Fetal insulin opposes this, so babies of diabetic mothers are at higher risk of respiratory distress syndrome.
- Insulin: Delays surfactant production (infants of diabetic mothers).
- Prolactin: Minor role.
- Oxytocin: Uterine contraction; no surfactant role.
- Aldosterone: Salt balance; no surfactant role.
7. A patient's arterial PO₂ is 65 mmHg with normal haemoglobin and cardiac output. Which type of hypoxia is this?
Answer: Hypoxic hypoxia. Hypoxic (hypoxaemic) hypoxia means low arterial PO₂: high altitude, hypoventilation, V/Q mismatch, shunt or diffusion problems. Anaemic hypoxia has normal PO₂ but low oxygen content. Stagnant hypoxia comes from low blood flow. Histotoxic hypoxia means cells cannot use oxygen (cyanide).
- Anaemic hypoxia: PO₂ is normal; haemoglobin is low.
- Stagnant (circulatory) hypoxia: Due to low cardiac output or local ischaemia.
- Histotoxic hypoxia: Cells cannot use oxygen; PO₂ normal.
- Carbon monoxide hypoxia: A form of anaemic hypoxia with normal PO₂.
References and dose sources
- BTS guideline for oxygen use in adults (Thorax 2017)
- NICE NG115: COPD in over 16s
- NICE NG106: Chronic heart failure
- BTS/NICE/SIGN asthma (NG245)
- Resuscitation Council UK — anaphylaxis
- BTS pleural disease
- NICE NG158 (VTE)
- NICE CG187 — acute heart failure
- NICE NG250 — pneumonia
- Salbutamol dosing: Drugs.com: Albuterol (salbutamol) dosage (see also our salbutamol dose page)
- Ipratropium bromide dosing: Drugs.com: Ipratropium dosage (see also our ipratropium bromide dose page)
- Furosemide dosing: Drugs.com: Furosemide dosage (see also our furosemide dose page)
- Glyceryl trinitrate (GTN) dosing: Drugs.com: Nitroglycerin dosage (see also our glyceryl trinitrate (gtn) dose page)
- Prednisolone dosing: Drugs.com: Prednisolone dosage (see also our prednisolone dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.