What is the protocol for using lung ultrasound in patient diagnosis and management?

Lung Ultrasound Protocol for Patient Diagnosis and Management

Lung ultrasound should be implemented as a point-of-care diagnostic tool using standardized scanning techniques and specific sonographic signs to diagnose and monitor acute respiratory conditions, with superiority over conventional chest radiography in most clinical settings. 1

Core Scanning Technique

Basic Eight-Region Protocol

• Perform systematic scanning of eight chest regions (four per hemithorax): upper anterior, lower anterior, upper lateral, and basal lateral areas, divided by the anterior and posterior axillary lines 1
• Use a microconvex probe (or linear probe for superficial structures) with a basic gray-scale ultrasound unit 2
• In critically ill patients, a rapid anterior two-region scan may suffice for initial assessment, particularly to rule out cardiogenic pulmonary edema 1
• For precise quantification, the 28-rib interspace technique can be employed, especially in cardiology and nephrology settings 1

Essential Sonographic Signs (The "Ten Signs")

Artifacts and Normal Findings

• Bat sign: Identifies the pleural line between rib shadows 2, 3
• Lung sliding: Dynamic movement of visceral against parietal pleura (produces "seashore sign" on M-mode); its presence rules out pneumothorax at that location 2, 3
• A-lines: Horizontal reverberation artifacts indicating normal aerated lung 2, 3

Pathological Findings

• B-lines: Vertical laser-like artifacts arising from the pleural line, indicating interstitial syndrome when ≥3 are present in one intercostal space 1
• Lung consolidation: Subpleural echo-poor region with tissue-like echotexture, seen in pneumonia, atelectasis, pulmonary embolism, or malignancy 1
• Pleural effusion: Identified by the "quad sign" (static view) and "sinusoid sign" (dynamic respiratory variation) 2, 3
• Pneumothorax: Absent lung sliding with "stratosphere sign" on M-mode; the "lung point" (transition between sliding and absent sliding) is pathognomonic 2, 3

Advanced Discriminatory Signs

• Lung pulse: Cardiac oscillations transmitted to consolidated lung, distinguishing atelectasis from pneumonia 2, 3
• Dynamic air bronchogram: Mobile air bronchograms suggest patent airways (pneumonia), while static ones suggest obstruction (atelectasis) 2, 3

Clinical Application Protocols

BLUE Protocol for Acute Respiratory Failure

Complete this rapid assessment in <3 minutes to differentiate causes of dyspnea 2, 3:

• Anterior bilateral lung rockets (≥3 B-lines) + lung sliding = "B-profile": Cardiogenic pulmonary edema 2, 3
• Anterior A-lines + abolished lung sliding = "A-profile": Pneumothorax or severe COPD/asthma 2, 3
• Anterior A-lines + posterior consolidation or effusion = "A/B profile": Pneumonia 2, 3
• Anterior A-lines + deep venous thrombosis = "C-profile": Pulmonary embolism 2, 3

FALLS Protocol for Circulatory Shock

Adapt the BLUE protocol sequentially to identify shock etiology 2, 3:

1. Assess for obstructive shock: right ventricle dilatation, pericardial tamponade
2. Evaluate for cardiogenic shock: left ventricle dysfunction, B-lines
3. Use B-line appearance as the endpoint for fluid resuscitation in hypovolemic shock 2, 3
4. Distributive shock: diagnosis of exclusion with normal cardiac function and absence of B-lines

Disease-Specific Applications

Interstitial Syndrome Assessment

• Define positive region: ≥3 B-lines in longitudinal plane between two ribs 1
• Define positive examination: ≥2 positive regions bilaterally in anterior chest zones 1
• Semiquantify severity by counting total B-lines (28-site technique) or number of positive scans (eight-region technique) 1
• Differentiate focal (pneumonia, contusion) from diffuse patterns (pulmonary edema, ARDS, fibrosis) 1

Lung Consolidation Evaluation

• Lung ultrasound differentiates consolidation etiologies (pneumonia vs. atelectasis vs. pulmonary embolism) with Level A evidence 1
• Use lower-frequency scanning for better depth penetration to assess consolidation extent 1
• Limitation: Cannot detect consolidations that do not reach the pleura 1

Pleural Effusion Management

• Ultrasound-guided thoracentesis is mandatory as it improves success rates and decreases pneumothorax risk compared to landmark technique 1
• Confirm fluid presence and guide needle placement in real-time 4

Monitoring Applications

• Track B-line changes to monitor therapy response in cardiogenic pulmonary edema (Level A evidence) 1
• Assess lung reaeration in ARDS/acute lung injury by documenting decreased B-lines and consolidation 1
• Monitor pulmonary congestion in hemodialysis patients, though clinical utility remains undetermined 1
• B-line assessment provides prognostic information for adverse outcomes and mortality in acute decompensated heart failure 1

Procedural Guidance Applications

Bronchoscopy Adjuncts

• Radial endobronchial ultrasound (R-EBUS) is recommended for peripheral lung nodules requiring tissue diagnosis, confirming ideal sampling location in real-time 1
• Electromagnetic navigation with ultrasound guidance increases diagnostic yield for peripheral lesions difficult to reach with conventional bronchoscopy 1

Thoracentesis

• Always use ultrasound guidance for diagnostic and therapeutic thoracentesis to minimize complications 1, 4

Key Advantages and Limitations

Advantages

• Superior to chest radiography for detecting interstitial syndrome, consolidation, and pleural effusion 1
• No ionizing radiation exposure, enabling the LUCIFLR program (Lung Ultrasound in the Critically Ill Favouring Limitation of Radiation) to postpone or eliminate many CTs 2, 3
• Portable, repeatable, real-time bedside assessment 5, 6
• Basic technique with steep learning curve, making it accessible to non-radiologists 1

Critical Pitfalls

• Cannot visualize lesions not reaching the pleural surface 1
• Requires adequate acoustic windows (obesity, subcutaneous emphysema limit visualization) 5
• Operator-dependent technique requiring proper training 7, 6
• B-lines are nonspecific; clinical context determines interpretation 1

Equipment Requirements

A cost-effective gray-scale ultrasound unit without Doppler capability is sufficient for lung ultrasound 2. A microconvex probe provides optimal versatility for whole-body scanning including lung assessment 2, 3.