II. Technique
- Transducer positioning
- Placement: Lung Apex (3rd intercostal space in a supine patient), mid-clavicular line
- Axis: Long axis with indicator at 12:00
- Direction: Perpendicular to chest
- Landmarks
- Artfacts
- A-Lines: Pleural line reverberation artfacts (horizontal lines at regular intervals)
- Normal finding
- B-Lines: Lung rockets (vertical wedges)
- Indicates Interstitial Edema
- Significant findings consistent with B-Lines
- Three or more rays in a single intercostal view (known as B+ lines)
- B-Lines start at the pleural line (not in the soft tissue)
- B-Lines descend the entire length of the screen
- B-Lines obscure A-Lines which are not typically visible
- B-Lines move with respiration
- Distinguish from similar artifacts
- Comet tail artifacts
- Partial rays that do not descend the length of the screen
- A-Lines typically still visible
- Superficial artifacts
- Rays start superficial to the pleural line
- Comet tail artifacts
- Generalized B-Lines
- Volume overload (e.g. CHF)
- ARDS
- Localized B-Lines
- A-Lines: Pleural line reverberation artfacts (horizontal lines at regular intervals)
-
Sliding Lung Sign present (normal findings)
- Marching-ants appearance
- Changes on M-mode
- Top: Bar code pattern (skin to pleura)
- Bottom: Seashore granular appearance (lung)
- Miscellaneous Findings
- Pleural Effusion
- Anechoic (black space) surrounds a triangle of well-defined lung
- Exudative fluid may appear hyperechoic (white)
- Consolidation
- Consolidated lung tissue appears similar to liver tissue on Ultrasound
- Pulmonary Edema
- Pneumonia
- Lung Contusion
- Lung Neoplasm
- PLAPS (Posterolateral alveolar and/or pleural syndrome)
- Best seen at the most posterior and inferior accessible point above the diaphragm in a supine patient
- Positive if Pleural Effusion or consolidation
- Pleural Effusion
III. Interpretation
- Pneumothorax
-
Pneumonia
- Focal or unilateral B-Lines (fluid in alveoli)
- Subpleural consolidation
- Consolidated lung tissue appears similar to liver tissue on Ultrasound
- Parapneumonic Effusion
- Interstitial Syndrome
- Excessive alveolar fluid as seen in CHF exacerbation
- Prominent B-Lines obscure other findings (and A-Lines disappear)
- Negative Lung Ultrasound
- Dyspnea due to COPD/Asthma, Pulmonary Embolism or non-respiratory cause (e.g. Anemia)
-
Pleural Effusion
- See Pleural Effusion
- More accurate than Chest XRay in detecting a Pleural Effusion (operator dependent)
- Detects Pleural Effusion volumes as small as 5 ml
- Test Sensitivity 94%, Test Specificity 98% (varies with operator experience)
- Identifies Pleural Fluid septations more accurately than CT
- Recommended for guiding Thoracentesis
IV. Efficacy
- Limited by shadowing from bullae (COPD), subcutaneous air, and tight rib spaces
-
POCUS in Acute Dyspnea speeds time to correct diagnosis
- Also increases the accuracy of CHF, Pneumonia, PE and Pleural Effusion diagnosis
- Does not appear to reduce mortality, hospital length of stay or readmission rates
- (2021) Ann Intern Med 147(7): 985-93 [PubMed]
V. Resources
- Ultrasound Podcast: Mike Stone, MD - Pulmonary Ultrasound Part 1 (ACEP 2014)
- Ultrasound Podcast: Mike Stone, MD - Pulmonary Ultrasound Part 2 (ACEP 2014)