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Pulmonary embolism is often a difficult and missed diagnosis. Unfortunately lung ultrasound will usually appear normal (lung sliding with A-lines) in patients with pulmonary embolism.
If you are concerned for pulmonary embolism, perform a cardiac ultrasound to look for right ventricular strain and a lower extremity DVT (deep vein thrombosis) scan rule out venous thromboemolism. If those ultrasounds are normal consider obtaining a CT angiogram of the chest to look for pulmonary embolism.
Chronic obstructive pulmonary disease (COPD) is a collection of lung diseases that obstruct airflow. This group of diseases can include asthma, emphysema, and chronic bronchitis. Patients with COPD or severe asthma often have hyperinflated lungs. If hyperinflation is severe enough, the resultant shallow breathing can reduce lung sliding.
If you see normal findings such as lung sliding and A-lines but the patient still has symptoms and difficulty breathing, you should consider COPD, asthma, pulmonary embolism, or nonpulmonary conditions causing the patient’s dyspnea.
Acute respiratory distress syndrome (ARDS) is often fatal and the risk of death increases with age and severity of the illness. ARDS is characterized by the rapid onset of widespread inflammation in the lungs. The most common cause of ARDS is sepsis, but can also be precipitated by inhalation of harmful substances, pancreatitis, aspiration, severe pneumonia, or near-drowning experiences. Notice how nearly all of these etiologies involve a form of fluid buildup or inflammation so ARDS will present with B-lines on thoracic ultrasound.
People with ARDS also have severe shortness of breath, rapid breathing, and may often need support from a ventilator.
Since the following ultrasound profile is similar to the profile of cardiogenic pulmonary edema, practitioners must use other clinical features to interpret these findings to rule out elevated left heart pressure as the cause of the B-lines.
ARDS Ultrasound Profile
Ultrasound is useful for assessing the severity of cardiogenic pulmonary edema. Cardiogenic pulmonary edema is a type of pulmonary edema caused by increased pressures of the left side of the heart. This condition often occurs secondary to congestive heart failure when the left ventricle cannot pump out all the blood it receives from the lungs. The backed-up blood increases capillary hydrostatic pressure that then causes fluid to leak into both lungs, resulting in bilateral and symmetric B-lines.
As CPE progresses, more B-lines appear until they converge into vertical sheets, known as confluent B-lines. As fluid builds up further, expect to see bilateral transudative pleural effusions with atelectasis of the lungs. Cardiogenic pulmonary edema usually affects both lungs but can atypically affect a unilateral lung.
If you suspect your patient has CPE, it is also recommended to perform an ultrasound evaluation of their heart to assess for systolic and diastolic dysfunction of the left ventricle.
Cardiogenic Pulmonary Edema – Lung Ultrasound Profile:
Pneumonia is an infection that inflames the alveoli and fills them with fluid. This extra fluid creates unilateral or bilateral B-lines depending if one or both lungs are affected.
The fluid or pus-filled alveoli also cause a productive cough with colored phlegm, fever, chills, and difficulty breathing.
Even the most experienced ultrasound practitioners have difficulty distinguishing pneumonia from atelectasis using ultrasound alone. Thus, a clear clinical picture is necessary before determining the true cause of lung consolidation. The table below outlines some of the key differentiating factors between pneumonia and atelectasis.
| Pneumonia | Atelectasis | |
| US Findings | – Consolidation pattern – Shred sign – Dynamic bronchograms – Possible pleural effusion (parapneumonic effusion) | – Consolidation pattern – Static air bronchograms |
| Distinguishing clinical features | – Fever and chills – Cough with colored mucous or blood – Severe Malaise – Crackles and breath sounds | – Obstruction to airway – Acute dyspnea – Mucous plug in Bronchus |
Ultrasound is incredibly useful for diagnosing pneumothorax with high sensitivity and specificity. A pneumothorax occurs when a lung collapses due to loss of negative pressure between the visceral and parietal pleurae. This abolishes lung sliding.
However, there is usually a location where sliding still exists. The transition from sliding to no sliding is known as the lung point sign. Though difficult to find, a lung point is 100% specific for ruling in a pneumothorax (Chan S.).
Clinical manifestations of pneumothorax include pleuritic chest pain, dyspnea, tachycardia, and reduced breath sounds on the affected side.
Here are three important steps to evaluating for pneumothorax:
Remember that presence of lung sliding only rules out pneumothorax at that specific point you are scanning. Make sure to maximize your sensitivity by scanning multiple points on the chest.
You can look for lung sliding with B-mode or M-mode:
Recall other causes of reduced/absent lung sliding: severe consolidation, chemical pleurodesis, acute infectious or inflammatory states, fibrotic lung diseases, acute respiratory distress syndrome, or mainstem intubation.
To confirm the presence of a pneumothorax, you should look for the “Lung Point Sign.“
The lung point is when you can see the transition between normal lung sliding and the absence of lung sliding. This is the transition point between the collapsed lung and normal lung. If you see this you can definitively rule in a pneumothorax. The Lung point sign also helps you quantify how large a pneumothorax is.
If you think you may have found a lung point but are not sure, use M-Mode and place your cursor at the intersection where you think lung sliding starts and stops. If you see a normal seashore sign that turns into an abnormal barcode sign, then you have located the lung point with M-Mode.
Now that you have a grasp of the most common pathological lung signs to look for, this section will help you use those findings to characterize more specifically the ultrasound profiles of pneumothorax, pneumonia, cardiogenic pulmonary edema, acute respiratory distress syndrome, and COPD.
You can choose to use an algorithm such as the Blue Protocol (Lichtenstein, et al) but after teaching many learners lung ultrasound we’ve found it much easier for you to recognize the lung ultrasound findings that go along with each disease pattern. We will present all of the major disease findings and give you examples of the corresponding lung ultrasound findings below.
Lung signs/findings specific to each disease will be further explained within their respective section. Keep in mind, these are the potential Lung ultrasound findings you will see at the bedside, however, you must coordinate these profiles clinically with what is going on with the patient.
| Pulmonary Pathology | Lung Ultrasound Findings |
| Pneumothorax | – No lung sliding/barcode sign – Lung point (hard to find) – Bilateral A-lines (parietal pleura reflection) |
| Pneumonia | – Consolidation or “hepatization of the lung” – Supleural Consolidations – “Shred” sign – Unilateral B-lines or bilateral B-lines – Possible small plural effusion – Reduced lung sliding due to thickened pleura in severe cases – Dynamic air bronchograms (atelectasis has static bronchograms) |
| Cardiogenic Pulmonary Edema | – Widespread and bilateral B-lines – Normal lung sliding – Possible bilateral effusion depending on the severity |
| Acute Respiratory Distress Syndrome (ARDS) | – Bilateral or unilateral B-lines – Normal lung sliding |
| COPD or Asthma | – Bilateral A-lines – Reduced lung sliding |
| Pulmonary Embolism (PE) | – Bilateral A-Lines – Deep Vein Thrombosis in Upper or Lower Extremities – Right Ventricular Enlargement (massive/submassive PE) |