David, a 34-year-old man, suffered a crush injury to his thorax whilst cutting trees in a garden. His co-worker took him to the emergency department. Upon arrival he was breathless and tachycardic. The doctor diagnosed a tension pneumothorax and inserted a chest drain.
a) Describe the pleural layers, their location/regions and arrangement. Explain the location of the pleural cavity.
The pleura are two serous membranes that surround the lungs. The parietal pleura covers:
- The inner surface of the thoracic wall.
- The upper surface of the diaphragm.
- The lateral surface of the mediastinum.
The parietal pleura is continuous with the visceral pleura at the lung hilum. The visceral pleura covers:
- The outer surface of the lung.
The pleural cavity is a potential space located between the parietal and visceral layers of pleura.
b) Define the term pneumothorax and explain the location of the problem.
A pneumothorax describes the presence of air within the pleural cavity, between the parietal and visceral layers of pleura.
c) Describe the physical examination findings associated with a left-sided tension pneumothorax.
- The left side of David’s thorax would be hyper-inflated
- Left-sided expansion would be reduced
- The left-side would be hyper-resonant compared to the right
- Breath sounds on the left would be reduced or absent
- The trachea would be deviated to the right.
- Compression of the mediastinum and a rightwards shift in position would also lead to impaired cardiac function, hypotension and tachycardia
d) Explain where you would insert a chest tube into David’s thorax
The chest tube would be inserted into the triangle of safety located on the lateral thoracic wall inferior to the axilla. The borders of the triangle are:
- The anterior and posterior axillary folds
- A horizontal line aligned approximately with the nipple* (~5th intercostal space)
e) Explain, with reasons, where the doctor would make an incision within a given intercostal space.
An intercostal space incision is made just above the lower rib of a given intercostal space. This is to avoid damage to the superiorly located intercostal neurovascular bundle. Incising just above the lower rib helps to also avoid the smaller accessory/collateral intercostal neurovascular bundle.
f) Describe in order (starting at the skin) the layers that would be cut through in order to insert a chest tube.
- Subcutaneous fat and tissue
- Serratus anterior
- External intercostal muscle
- Internal intercostal muscle
- Innermost intercostal muscle
- Endothoracic fascia
- Parietal pleura – at this point the doctor would now be in the pleural cavity and should STOP HERE. If he/she continued to cut through any more layers they would pierce the visceral pleura and then damage the lung – not ideal!
* Try not to use the nipples as a landmark for surface anatomy because the positions of nipples vary across individuals! I’ve just put it in the answer as a rough estimate of location but for safety always double check with your intercostal spaces!