Acute respiratory distress & tachypnoea
Heart plus lung ultrasound at the bedside: pulmonary oedema, PE, pneumothorax, pneumonia or tamponade.
Echo approach, step by step
In acute respiratory failure, lung ultrasound following the BLUE protocol gave the correct diagnosis in about 90% of patients [199]. Focused cardiac ultrasound adds LV and RV function, valves and pericardium. Together they separate the cardiac from the pulmonary causes within minutes [152,202].
- Lung sliding (anterior)Absent sliding with a lung point = pneumothorax [199,202].
- Anterior B-linesBilateral diffuse B-lines (B-profile) = pulmonary oedema; asymmetric or with consolidation = pneumonia or ARDS [199].
- A-profile (normal anterior lung)Check the leg veins: DVT → PE; posterolateral consolidation or effusion → pneumonia; neither → COPD or asthma [199].
- LVLVEF, regional wall motion, E/e′ [2].
- Acute valve lesionFlail mitral leaflet or acute AR: the LV may be normal-sized and hyperdynamic [4].
- RVDilatation, McConnell, D-shaped LV → PE [124].
- PericardiumEffusion with tamponade [149].
- IVCSize and variation.
- Lung sliding
- B-line profile
- DVT scan if A-profile
- LVEF, RWMA
- Acute MR / AR
- RV size
- Effusion
Causes & echo clues
| Cause | Lung ultrasound | Heart | Next |
|---|---|---|---|
| Cardiogenic pulmonary oedema | Bilateral B-lines | Low EF or high E/e′, or acute valve lesion | Nitrates, diuretics, NIV [12,199] |
| Pulmonary embolism | A-profile, DVT | Dilated RV | CTPA or thrombolysis if shock [124,199] |
| Pneumonia / ARDS | Consolidation, asymmetric B-lines | Usually normal | Cultures, antibiotics [199] |
| Pneumothorax | No sliding, lung point | — | Decompression [199] |
| COPD / asthma exacerbation | A-profile without DVT | RV strain possible | Bronchodilators [199] |
| Tamponade | Variable | Effusion with collapse | Drainage [149] |
| Metabolic acidosis (sepsis, DKA) | Normal | Hyperdynamic | Blood gas, lactate [155] |
Clinical pathway to the diagnosis
- StabiliseOxygen, position, and non-invasive ventilation for pulmonary oedema or COPD.
- Arterial blood gasType 1 or type 2 failure, acidosis, lactate.
- Bedside ultrasoundBLUE protocol and focused echo [199,202].
- ECG, chest X-ray, NT-proBNP, troponin, D-dimeras indicated [12,124].
- CTCTPA or CT chest when the diagnosis remains uncertain.
Clinical pearls & pitfalls
PitfallAcute severe MR (papillary rupture, chordal rupture, endocarditis) causes flash pulmonary oedema with a normal-sized, hyperdynamic LV and a jet that may look small because of rapid pressure equalisation [4,138].
- Flash pulmonary oedema with preserved EF → hypertensive crisis, transient ischaemic MR, renal artery stenosis [26].
- B-lines are not specific to the heart. Interstitial lung disease and ARDS also produce them. Pleural line irregularity and consolidation favour lung disease [202].
- Tachypnoea with a clear chest and a normal heart → metabolic acidosis, sepsis or early PE [124,155].
Red flags
- SpO₂ <90% despite oxygen, silent chest, exhaustion
- Hypotension → cardiogenic or obstructive shock [153]
- Unilateral absent breath sounds with hypotension → tension pneumothorax [199]
- Tachypnoea with clear lungs → PE, metabolic acidosis, sepsis [124,155]