Lung ultrasonography (synonyms: ultrasound of the lungs; Lung ultrasonography, LUS) is used for diagnosis in the leading symptom “acute respiratory distress”. It is used as a bedside “point-of-care ultrasound procedure” in certain clinical situations (see below) and is performed independently by emergency and acute care physicians. Pulmonary sonography is a component of thoracic sonography.The procedure allows multiple progress monitoring during surveillance without exposing the patient to X-rays. Thus, particularly vulnerable patient groups, (children, pregnant women) can be examined without radiation exposure.
Indications (areas of application)
- Differential diagnosis of:
- Heart failure (cardiac insufficiency)
- Pulmonary artery embolism (LAE)
- Pulmonary edema – edema (accumulation of water) in the lungs.
- Pericardial effusion (pericardial effusion)
- Pleural effusion – pathological (abnormal) increase in fluid content between the pleura parietalis (pleura) and pleura visceralis (pleura).
- Pneumothorax – collapse of the lung caused by an accumulation of air between the visceral pleura (lung pleura) and the parietal pleura (chest pleura).
- Pneumonia (pneumonia)
- Thoracic wall infiltration of a lung carcinoma (ingrowth of a lung cancer into the chest wall).
The procedure
Pulmonary sonography is performed using a low-frequency sector or convex transducer (2-5 MHz) in terms of B-line diagnostics in 8 quadrants of the lung (4 per thoracic side/chest side). The transducer is placed intercostally (“located between two ribs“). The ultrasound plane is aligned parallel to the longitudinal course of the ribs. Note: There is a close correlation between pulmonary venous congestion (“pulmonary venous congestion”) and interstitial (“located in the interstitial tissue”) fluid collections in which B-lines appear. Bilateral (both sides) detection in at least 2 regions and more than 3 B-lines per sonic window can diagnose pulmonary (lung-related) congestion with a sensitivity (percentage of diseased patients in whom the disease is detected by use of the test, i.e., a positive test result occurs) of 100% and a specificity (probability that actually healthy individuals who do not have the disease in question are also detected as healthy by the test) of 92%. That is, a physiological lung has 0-2 B-lines. Pulmonary venous congestion confirms the suspected diagnosis of acute heart failure. Studies demonstrate a sensitivity of 70-85% and a specificity of 75-83% for this. Specificity for detecting acute heart failure increases to 100% when sequential sonography of the heart, inferior vena cava (“inferior vena cava”), and lungs is used.Detection of B-lines: ≥ 3 per field of view in 2 of 4 areas bilaterally.
Pulmonary artery embolism (LAE) is seen in the right dorsal (“affecting the back”) lower lobe in two-thirds of all cases. Using a linear transducer, subpleural lesions (often triangular or round > 5 mm) close to the thoracic wall can be detected (= peripheral LAE). Subsequently, compression ultrasonography of the leg veins (see “Ultrasonography of venous vessels” below) should be performed to detect deep vein thrombosis.Detection of B-lines: Number 0-2
Pulmonary edema shows echo phenomena: comet tail artifacts due to multiple acoustic interfaces between small water-rich structures and surrounding alveolar air in the lung periphery. The sensitivity of ultrasound (percentage of diseased patients in whom the disease is detected by the use of the procedure, i.e., a positive finding occurs) was 96% vs. 65% radiothorax; specificity (probability that actually healthy individuals who do not have the disease in question are also detected as healthy in the test): 88% vs. 96%
Pleural sonography (ultrasound examination of the pleura (pleura) and pleural space) using a sector or convex transducer can detect even small amounts of pleural effusion. An effusion height of 10 cm corresponds to approximately a volume of 1-2 l.Detection of B-lines: regionally possibleSonography is now the primary imaging method for pericardial effusions as well. Because lung sliding, i.e., the dynamic, respiratory-dependent movement of the visceral pleura, is usually well detected on the B-scan, pneumothorax can be readily identified in its absence.After placement of a pleural drain, a chest x-ray is performed to determine the volume of the pneumothorax.Detection of B-lines: Exclusion
In the case of pneumonia, echo-rich, lenticular internal echoes can be detected in pulmonary infiltrates near the thorax due to air in the small bronchi (tubular structures in the lungs) (= pneumonic infiltrate). Detection of B-lines: often regional, increased around consolidationsParapneumonic pleural effusion can be detected in 50% of all patients with pneumonia.Pulmonary sonography is also an alternative to chest/thoracic radiography when pneumonia is suspected in children.