Chest Trauma
Pneumothorax - Tension
Tension pneumothorax
Tension pneumothorax is the progressive build-up of air within the pleural space, usually due to a lung laceration which allows air to escape into the pleural space but not to return. Positive pressure ventilation may exacerbate this 'one-way-valve' effect.
Progressive build-up of pressure in the pleural space pushes the mediastinum to the opposite hemithorax, and obstructs venous return to the heart. This leads to circulatory instability and may result in traumatic arrest. The classic signs of a tension pneumothorax are deviation of the trachea away from the side with the tension, a hyper-expanded chest, an increased percussion note and a hyper-expanded chest that moves little with respiration. The central venous pressure is usually raised, but will be normal or low in hypovolaemic states.
However these classic signs are usually absent and more commonly the patient is tachycardic and tachypnoeic, and may be hypoxic. These signs are followed by circulatory collapse with hypotension and subsequent traumatic arrest with pulseless electrical activity (PEA). Breath sounds and percussion note may be very difficult to appreciate and misleading in the trauma room.
Tension pneumothorax may develop insidiously, especially in patients with positive pressure ventilation. This may happen immediately or some hours down the line. An unexplained tachycardia, hypotension and rise in airway pressure are strongly suggestive of a developing tension.
The X-ray on the right is a post-mortem film taken in a patient with severe blunt trauma to the chest and a left tension pneumothorax. It illustrates the classic features of a tension:
Deviation of the trachea away from the side of the tension.
Shift of the mediastinum
Depression of the hemi-diaphragm
With this degree of tension pneumothorax, it is not difficult to appreciate how cardiovascular function may be compromised by the tension, due to obstruction of venous return to the heart. This massive tension pneumothorax should indeed have been detectable clinically and, in the face of haemodynamic collapse, been treated with emergent thoracostomy - needle or otherwise.
A tension pneumothorax may develop while the patient is undergoing investigations, such as CT scanning (image at right) or operation. Whenever there is deterioration in the patient's oxygenation or ventilatory status, the chest should be re-examined and tension pneumothorax excluded.
The presence of chest tubes does not mean a patient cannot develop a tension pneumothorax. The patient below had a right sided tension despite the presence of a chest tube. It is easy to appreciate how this may happen on the CT image showing the chest tubes in the oblique fissure. Chest tubes here, or placed posteriorly, will be blocked as the overlying lung is compressed backwards. Chest tubes in supine trauma patients should be placed anteriorly to avoid this complication. Haemothoraces will still be drained provided the lung expands fully.
The CT scan also shows why the tension is not visible on the plain chest X-ray - the lung is compressed posteriorly but extends out to the edge of the chest wall, so lung markings are seen throughout the lung fields. However there is midline shift compared to the previous film.
Chest TraumaPneumothorax - TensionTension pneumothoraxTension pneumothorax is the progressive build-up of air within the pleural space, usually due to a lung laceration which allows air to escape into the pleural space but not to return. Positive pressure ventilation may exacerbate this 'one-way-valve' effect.Progressive build-up of pressure in the pleural space pushes the mediastinum to the opposite hemithorax, and obstructs venous return to the heart. This leads to circulatory instability and may result in traumatic arrest. The classic signs of a tension pneumothorax are deviation of the trachea away from the side with the tension, a hyper-expanded chest, an increased percussion note and a hyper-expanded chest that moves little with respiration. The central venous pressure is usually raised, but will be normal or low in hypovolaemic states.However these classic signs are usually absent and more commonly the patient is tachycardic and tachypnoeic, and may be hypoxic. These signs are followed by circulatory collapse with hypotension and subsequent traumatic arrest with pulseless electrical activity (PEA). Breath sounds and percussion note may be very difficult to appreciate and misleading in the trauma room.Tension pneumothorax may develop insidiously, especially in patients with positive pressure ventilation. This may happen immediately or some hours down the line. An unexplained tachycardia, hypotension and rise in airway pressure are strongly suggestive of a developing tension.The X-ray on the right is a post-mortem film taken in a patient with severe blunt trauma to the chest and a left tension pneumothorax. It illustrates the classic features of a tension:Deviation of the trachea away from the side of the tension.Shift of the mediastinumDepression of the hemi-diaphragmWith this degree of tension pneumothorax, it is not difficult to appreciate how cardiovascular function may be compromised by the tension, due to obstruction of venous return to the heart. This massive tension pneumothorax should indeed have been detectable clinically and, in the face of haemodynamic collapse, been treated with emergent thoracostomy - needle or otherwise.A tension pneumothorax may develop while the patient is undergoing investigations, such as CT scanning (image at right) or operation. Whenever there is deterioration in the patient's oxygenation or ventilatory status, the chest should be re-examined and tension pneumothorax excluded.The presence of chest tubes does not mean a patient cannot develop a tension pneumothorax. The patient below had a right sided tension despite the presence of a chest tube. It is easy to appreciate how this may happen on the CT image showing the chest tubes in the oblique fissure. Chest tubes here, or placed posteriorly, will be blocked as the overlying lung is compressed backwards. Chest tubes in supine trauma patients should be placed anteriorly to avoid this complication. Haemothoraces will still be drained provided the lung expands fully.
The CT scan also shows why the tension is not visible on the plain chest X-ray - the lung is compressed posteriorly but extends out to the edge of the chest wall, so lung markings are seen throughout the lung fields. However there is midline shift compared to the previous film.
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