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.
Ultrasound Profile of Pneumothorax
- No lung sliding
- M-mode barcode sign
- Lung point Sign
- A-lines from intact parietal pleura
Here are three important steps to evaluating for pneumothorax:
First, if lung sliding is present, you can rule out pneumothorax with 100% accuracy at that ultrasound point (Husain LF).
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:
Second, if lung sliding is ABSENT, you should not automatically assume pneumothorax.
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.
Third, if a lung point is present, you can rule in pneumothorax with 100% accuracy (Chan S).
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.