Medical Student Clinical Pearl
Vlad Kovalik
MD Candidate, 2019
Dalhousie University Faculty of Medicine
Reviewed and Edited by Dr. David Lewis
A 90-year-old female presented to the emergency department after a fall. Her vitals were stable and a chest x-ray demonstrated three posterior rib fractures. She was keen to be managed at home and had the necessary supports in place. She was discharged with a prescription for analgesics and instructions to return to the ED if her condition changed.
4 days later, the same patient returned to the emergency department with shortness of breath and increased work of breathing. Auscultation revealed decreased air entry on the left. A pneumothorax was at the top of the differential.
PoCUS for Pneumothorax
Lung ultrasound has been found to be more sensitive than chest x-ray for detecting pneumothorax.1 To begin scanning, it is best to have the patient in a supine or semi-recumbent position. The high frequency linear array transducer provides excellent near-field imaging and may be used to better appreciate Lung Sliding, however both the phased array or curvilinear probe may also be used. The probe should be positioned in the longitudinal orientation, with the marker towards the patient’s head, on the anterior chest. Scanning through various rib spaces on both sides completes the exam.
In a normal healthy lung, the visceral and parietal pleura slide against each other creating a distinct shimmering effect known as Lung Sliding. The presence of Lung Sliding rules out pneumothorax with nearly 100% sensitivity in the area directly under the probe.2 *
Comet-tails are another normal feature of a healthy lung. This is an artifact caused by the reverberation between the parietal and visceral pleura. Comet-tails are seen as bright, vertical lines that fade quickly. The detection of comet tails allows you to rule-out pneumothorax.3
The Seashore Sign is a normal finding in M-mode of a healthy lung. The sliding of the parietal and visceral pleura creates a sand like pattern directly deep to the pleural line. In a pneumothorax, there is air between the parietal and visceral pleura and thus the ultrasound beam is scattered deep to the parietal pleura. In this case, an artifact known as the Barcode Sign may be seen where a reflection of the chest wall is seen below the parietal pleura.5 *
The most specific finding of pneumothorax is the Lung Point Sign. This is the point where the visceral pleura begins to separate from the parietal pleura indicating the boundary of the pneumothorax. Although pathognomonic for pneumothorax it is not always present – the sensitivity is 66%.4
In summary
PoCUS for pneumothorax can be performed quickly at the bedside and is more sensitive than chest x-ray. Look for the absence of Lung Sliding, the absence of Comet-tails and try to locate the Lung Point Sign.
