A 26 year old man is brought to ED with a stab wound to his chest. The knife is still in situ is in the 4th intercostal midclavicular line. He has had a needle decompression for a presumed left pneumothorax and the needle is still in situ in the left 2nd intercostal space.

On examination

  • GCS 15
  • HR 113/min
  • BP 86/40

This is the ultrasound of his left lung anteriorly.

There is lung sliding. This is the the back and forth motion at the level of the pleural line.  Lung sliding indicates there is no pneumothorax. If a pneumothorax were present sound waves would not be able to reach the visceral pleura as sound waves are 99.9% reflected back form an air/tissue interface.

There are also ring down artifacts. The ring down artifacts also indicate there is no pneumothorax. A ring down artifact is produced by reverbation between alveoli indicating that sound waves are reaching the visceral pleura.  Therefore there is no air separating the visceral from the parietal pleura as would be the case if a pneumothorax were present.

There is a pleural effusion in the LUQ indicating a likely haemothorax. Visualisation of the continuation of the spine beyond the costophrenic angle (star; see below)) indicates that sound waves are penetrating beyond the diaphragm which is only possible if aerated lung has been displaced by fluid. This is called a +ve spine sign.

 

A modified parasternal long axis view shows a large haemocardium (depth of 1.49 cm). The blood is coagulated and appears hyperechoic in the pericardial space.

 

Discussion

The use of ultrasound in chest trauma by trained ED physicians is helpful in the early diagnosis of pneumothorax and haemothorax. A recent study  (1) comparing the sensitivity and specificity of  US with CXR  showed that the sensitivities of US in detecting pneumothorax and hemothorax were higher than that of CXR. The specificities of US in detecting pneumothorax and hemothorax were comparable to that of CXR. In a time sensitive situation  as with this haemodynamically unstable patient, it is an invaluable skill to have.

The importance of point of care ECHO in the diagnosis of pericardial effusion in thoracic trauma has been well described and established (2). Clinical signs and symptoms of pericardial effusion and cardiac tamponade are unreliable in the context of chest trauma. The ability to detect a pericardial effusion early by emergency physicians and trauma surgeons impacts patient management decisions and may decrease the time to definitive surgical care, thus optimizing chances for good outcomes.

In trauma as little as 100 – 200 mls of of blood may elevate pericardial pressures to 30 mmHg or more defining severe cardiac tamponade.  This is because the fibrous parietal pericardium has a limit to it’s elasticity. The elasticity of the pericardium is dependent on how fast the fluid is accumulated. In the case of trauma, this is sudden and the pericardium reaches it’s elasticity quickly  above which diastolic compliance is reduced, venous return is compromised and ventricular interdependence becomes haemodynamically important.

Some points to remember

  1. Blood in the pericardium may clot quickly as it is restricted by the confines of the pericardial space. On ultrasound it will appear hyperechoic if clotted.
  2. Blood in the thorax has more space to accumulate and generally will clot less quickly. There may also be active ongoing pulmonary haemorrhage in the trauma situation. Fresh blood is anaechoic.
  3. When looking for a pneumothorax in trauma is may be better to use a linear probe lung sliding using a curvilinear probe is not clear. This can occur in a patient who is hypoventilating for example.  The higher frequency probe which will show the pleural line better and make  lung sliding easier to see.
  4. Air rises. In the supine patient put the probe on the highest point of the chest as you may otherwise miss a pneumothorax.
  5. Always use the curvilinear probe when looking at the RUQ or LUQ for a pleural effusion or consolidation. The curvilinear probe has a lower frequency and therefore better tissue penetration.

Put the probe at the highest point of the chest to avoid missing a pneumothorax

 

References

  1. Cureus 2023 Aug 31;15(8):e44456. doi: 10.7759/cureus.44456.
    Comparing Sensitivity and Specificity of Ultrasonography With Chest Radiography in Detecting Pneumothorax and Hemothorax in Chest Trauma Patients: A Cross-Sectional Diagnostic StudyAswin K 1, Balamurugan S 2, Ramkumar Govindarajalou 3, Ganesh Kumar Saya 4, Elamurugan Tp 2, Gunaseelan Rajendran 5
  2. Emergency Medicine Clinics of North America Volume 16, Issue 1, 1 February 1998, Pages 191-207 ECHOCARDIOGRAPHY IN THORACIC TRAUMA Dennis Chan MD, FACEP, FAAEM *