📚 Guideline basis
Volpicelli G, et al. International evidence-based recommendations for point-of-care lung ultrasound (Intensive Care Med 2012); Lichtenstein D — the BLUE protocol and subsequent work on integrated lung–heart assessment (Intensive Care Med 2022, PMID 35187694); ESICM 2025 haemodynamic recommendations; ERS/ESICM statements on diaphragm ultrasound.
Why integration outperforms either modality alone
Cardiac and lung ultrasound each answer questions the other cannot, and their combination is diagnostically specific where each alone is not. A dilated inferior vena cava is ambiguous; a dilated IVC with diffuse B-lines and an E/e′ of 18 is not. Diffuse B-lines are ambiguous; diffuse B-lines with a normal E/e′ and a normal-sized left atrium are not.
The integration is not an add-on. In acute respiratory failure and in undifferentiated shock it is the examination.
Lung ultrasound fundamentals
The lung is imaged through what it does to the ultrasound beam rather than by direct visualisation — normal aerated lung is an impenetrable air–tissue interface, and the diagnostic information is artefactual.
Sign | Appearance | Meaning |
Lung sliding | Shimmering movement of the pleural line with respiration; "seashore" on M-mode | Visceral and parietal pleura in apposition — excludes pneumothorax at that point |
A-lines | Horizontal repetitions of the pleural line at regular intervals | Normally aerated (or hyperinflated) lung; "dry" |
B-lines | Vertical, laser-like hyperechoic artefacts arising from the pleural line, extending to the bottom of the screen, erasing A-lines, moving with sliding | Interstitial syndrome. ≥ 3 B-lines in a single intercostal space defines a positive field |
Lung point | The transition point where sliding appears and disappears within one image | Pathognomonic of pneumothorax; 100% specific |
Barcode / stratosphere sign | Absence of sliding on M-mode | Pneumothorax, but also mainstem intubation, apnoea, pleural adhesions, ARDS, severe COPD |
Consolidation | Tissue-like ("hepatised") lung with irregular deep border | Pneumonia, atelectasis, contusion, infarction |
Air bronchogram | Punctate or linear hyperechoic foci within consolidation; dynamic if they move with respiration | Dynamic air bronchograms favour pneumonia over resorptive atelectasis |
Fluid bronchogram | Anechoic branching structures within consolidation | Obstructive atelectasis |
Pleural effusion | Anechoic space with the "sinusoid sign" on M-mode; "quad sign" | Effusion; complex septated appearance suggests exudate or empyema |
The BLUE protocol profiles
Profile | Findings | Leading diagnosis |
A-profile with lung sliding, no DVT | Bilateral A-lines | Asthma / COPD |
A-profile with DVT on venous compression | Bilateral A-lines, positive compression study | Pulmonary embolism |
B-profile | Bilateral anterior diffuse B-lines with sliding | Pulmonary oedema |
A/B-profile or C-profile | Asymmetric — B-lines on one side, or anterior consolidation | Pneumonia |
A′-profile with lung point | Absent sliding plus lung point | Pneumothorax |
PLAPS (posterolateral alveolar/pleural syndrome) | Posterolateral consolidation or effusion | Pneumonia |
The protocol is deliberately simple and achieves high diagnostic accuracy for the common causes of acute respiratory failure. Its value in this book is as the respiratory half of a combined assessment.
The composite diagnostic table
This is the practical core of the chapter.
Lung pattern | Cardiac findings | Composite diagnosis | Immediate action |
A-lines (dry) | Small hyperdynamic LV, collapsing IVC | Hypovolaemia | Fluid is indicated |
A-lines | Normal LV, low Ea, high VTI | Vasoplegic shock | Vasopressor |
A-lines | Dilated RV, septal shift, plethoric IVC | Acute cor pulmonale or pulmonary embolism | Chapters 32, 33; not fluid |
A-lines with positive femoral compression | Dilated RV | Pulmonary embolism | Reperfusion pathway |
Diffuse bilateral B-lines | Low EF, high E/e′, dilated LA, dilated IVC | Cardiogenic pulmonary oedema | Diuresis, afterload reduction |
Diffuse bilateral B-lines | Normal EF, normal E/e′, normal LA | ARDS / non-cardiogenic oedema | Lung-protective ventilation |
Diffuse B-lines, irregular pleural line, spared areas, subpleural consolidation | Normal filling pressures | ARDS | Ventilator strategy |
Focal B-lines with consolidation and dynamic air bronchograms | Variable | Pneumonia | Antimicrobials |
Absent sliding with lung point | Underfilled chambers | Tension pneumothorax | Decompression |
Large effusion | Compressed chambers | Effusion ± tamponade physiology | Drainage |
B-lines + free intraperitoneal fluid | Small hyperdynamic LV | Haemorrhage with transfusion-associated oedema | Chapter 37 |
Distinguishing cardiogenic oedema from ARDS
Both produce bilateral B-lines. The lung findings themselves discriminate partially; the cardiac findings discriminate better.
Feature | Cardiogenic | ARDS |
B-line distribution | Homogeneous, gravity-dependent, symmetric | Patchy, with spared areas, asymmetric |
Pleural line | Smooth, regular, thin | Thickened, irregular, fragmented |
Subpleural consolidations | Absent | Common |
Pleural effusions | Common, bilateral | Less common |
E/e′ | Elevated (average > 14) | Normal |
LA volume index | Enlarged | Usually normal |
TR velocity | ≥ 2.8 m/s (post-capillary) | Variable; PASP may be raised with normal LAP indices |
Response to diuresis | B-lines clear rapidly | Little change |
The two coexist frequently. The clinical question is rarely "which one" but "how much of each", and the E/e′ plus TR velocity pair is the most useful discriminator obtainable at the bedside.
B-line quantification for fluid management
B-line burden correlates with extravascular lung water and can be scored to guide fluid removal.
- 8-zone scan (anterior and lateral, upper and lower, bilaterally) is the practical ICU compromise; 28-zone scoring exists for research.
- A field is positive at ≥ 3 B-lines in one intercostal space.
- Total B-line count or the number of positive zones is trended.
Applications: titrating diuresis or ultrafiltration; detecting fluid intolerance during resuscitation (Chapter 12); identifying weaning-induced pulmonary oedema (Chapter 34); and prognostication in heart failure.
B-lines are not specific to cardiogenic oedema — they occur in ARDS, pneumonia, pulmonary fibrosis, and contusion. Their use as a fluid-tolerance marker rests on the change within a patient, not the absolute count.
Diaphragm ultrasound
The third component of a complete cardiopulmonary assessment, relevant chiefly to weaning (Chapter 34).
Measurement | Technique | Interpretation |
Thickening fraction | High-frequency linear probe in the zone of apposition (8th–10th intercostal space, mid-axillary); (T_insp − T_exp) / T_exp | Reduced values are associated with weaning failure; commonly cited thresholds fall in the 20–30% range, and they vary between studies |
Excursion | Curvilinear probe, subcostal, M-mode through the hemidiaphragm | Reduced excursion (commonly cited thresholds around 10–11 mm) is associated with weaning failure |
End-expiratory thickness | Same window | Serial thinning indicates ventilator-induced diaphragmatic atrophy |
⚠️ Evidence quality
Diaphragm ultrasound thresholds vary considerably across studies and are not standardised in a society guideline. They identify diaphragm dysfunction as a contributor to weaning failure; they do not predict individual weaning outcomes reliably enough to be used alone.
Venous ultrasound for deep vein thrombosis
Two-point or three-point compression of the common femoral and popliteal veins. Non-compressibility indicates thrombus.
Its value in this book is Bayesian: in a shocked patient with RV dysfunction and no alternative explanation, a positive compression study raises the post-test probability of pulmonary embolism substantially and, in a patient too unstable for CT, can justify reperfusion (Chapter 33). It takes under two minutes and is routinely omitted.
An integrated bedside protocol
Order matters — acquire the findings that change management fastest first.
- Anterior chest, both sides — sliding, A- versus B-profile, lung point (30 seconds; excludes tension pneumothorax)
- Subcostal cardiac — effusion, RV:LV ratio, gross LV function
- Subcostal IVC — size and variation
- Parasternal and apical — chamber assessment, LVOT VTI, E/e′, TR velocity
- Lateral and posterolateral lung zones — B-line count, effusion, consolidation
- Femoral and popliteal compression — if PE is in the differential
- Abdominal windows — if trauma or haemorrhage is in the differential
- Diaphragm — if the question is weaning
The whole sequence takes 8–12 minutes and answers most questions in acute respiratory failure and undifferentiated shock.
🛑 Critical pitfall: Diagnosing pneumothorax on absent lung sliding alone. Absent sliding also occurs with mainstem intubation, apnoea, pleural adhesions, severe COPD, ARDS and prior pleurodesis. The lung point is the specific sign.
🛑 Critical pitfall: Interpreting B-lines as "fluid overload" without cardiac correlation. ARDS produces B-lines with entirely normal filling pressures, and diuresing that patient causes harm.
🛑 Critical pitfall: Giving fluid to a patient with an A-line profile and a collapsing IVC without looking at the right ventricle. In acute cor pulmonale the lungs can be dry and the fluid still harmful.
- 💡 Clinical pearl: A-lines with a small hyperdynamic ventricle and a collapsing IVC is the strongest bedside indication for fluid available. The same cardiac picture with diffuse B-lines is a contraindication.
- 💡 Clinical pearl: Hand the B-line count over to the nursing and physiotherapy teams. It is the most transferable, reproducible measure in this chapter and converts fluid management into a trended variable.
- 💡 Clinical pearl: Add bilateral leg vein compression to any study performed for unexplained shock with a dilated right ventricle. Two minutes, and occasionally decisive.
References
- Volpicelli G, Elbarbary M, Blaivas M, et al. International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med 2012;38:577–91.
- Lichtenstein DA, Mezière GA. Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol. Chest 2008;134:117–25.
- Lichtenstein D, et al. Lung and cardiac ultrasound integration in critical care. Intensive Care Med 2022. PMID 35187694.
- Zambon M, Greco M, Bocchino S, et al. Assessment of diaphragmatic dysfunction in the critically ill patient with ultrasound: a systematic review. Intensive Care Med 2017;43:29–38.
- ESICM. 2025 recommendations on haemodynamic monitoring in shock. Intensive Care Med 2025.