Thorax

There are six potentially life-threatening injuries (two contusions and four "ruptures') that may be identified by careful examination of the chest during the secondary survey:

• Pulmonary contusion

• Cardiac contusion

• Aortic rupture

• Diaphragmatic rupture

• Oesophageal rupture

• Rupture of the tracheobronchial tree Pulmonary Contusion

Inspection of the chest may reveal signs indicating considerable decelerating forces, such as seat belt bruising. Even in the absence of rib fractures, pulmonary contusion is the commonest potentially lethal chest injury. Young adults and children have particularly compliant ribs and considerable energy can be transmitted to the lungs in the absence of rib fractures. The earliest indication of pulmonary contusion is hypoxaemia (reduced PaO2:FIO2 ratio). Chest X-ray will show patchy infiltrates over the affected area but it may be normal initially. Increasing the FIO2 alone may provide sufficient oxygenation but failing that the patient may require mask CPAP or tracheal intubation and positive-pressure ventilation. Ventilator parameters should be continually appraised. Small tidal volumes (5-7 ml/kg) will minimise volutrauma. Keeping the peak inspiratory pressure < 35 cmH2O and FIO 2 < 0.5 is desirable. No specific ventilatory mode has been proven superior to any other. The patient with chest trauma requires appropriate fluid resuscitation but fluid overload will compound the lung contusion.

Cardiac Contusion

Cardiac contusion must be considered in any patient with severe blunt chest trauma, particularly those with sternal fractures. Cardiac arrhythmias and ST changes on the ECG may indicate contusion but these signs are very non specific. Elevated CPK-MB isoenzymes are equally insensitive for diagnosing myocardial contusion. An elevated CVP in the presence of hypotension will be the earliest indication of myocardial dysfunction secondary to severe cardiac contusion, but cardiac tamponade must be excluded. Most clinicians will use echocardiography to confirm the diagnosis of cardiac contusion, but radionuclide scintigraphy is probably the Gold Standard. The right ventricle is most frequently injured as it is predominantly an anterior structure. Patients with severe cardiac contusion tend to have other serious injuries that will mandate their admission to an intensive care unit. Thus, the decision to admit a patient to ITU rarely depends on the diagnosis of cardiac contusion alone. The severely contused myocardium is likely to require inotropic support.

Traumatic Aortic Rupture

The thoracic aorta is at risk in any patient sustaining a significant decelerating force (e.g. fall from a height or high speed road traffic accident). Only 10-15% of these patients will reach hospital alive and of these survivors, two thirds will die of delayed rupture within 2 weeks. The commonest site for aortic injury is at the aortic isthmus, just distal to the origin of the left subclavian artery at the level of the ligamentum arteriosum. Deceleration produces huge shear forces at this site because the relatively mobile aortic arch travels forward relative to the fixed descending aorta. The tear in the intima and media may involve either part or all of the circumference of the aorta and in survivors the haematoma is contained by an intact aortic adventitia and mediastinal pleura. Patients sustaining traumatic aortic rupture usually have multiple injuries and may be hypotensive at presentation. However, upper extremity hypertension is present in 40% of cases as the haematoma compresses the true lumen causing a "pseudo-coarctation'. The supine chest radiograph will show a widened mediastinum in the vast majority of cases. Although this is a sensitive sign of aortic rupture, it is not very specific. An erect chest radiograph provides a clearer view of the thoracic aorta (Figure TT.8). Other signs suggesting possible rupture of the aorta are listed in Figure TT.9.

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Figure TT.8

Radiological features of traumatic aortic rupture

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