21 BLUNT THORACIC TRAUMA
Jeffrey L. Johnson M.D., Ernest E. Moore M.D.

1. How often do patients with isolated blunt chest trauma need an emergent operation?

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Rarely. In patients who arrive in the hospital alive, operative injuries to the pulmonary, vascular, and mediastinal structures are surprisingly rare; only 5% of patients with isolated blunt injury to the chest require thoracotomy.

2. In a patient with a hemothorax after blunt chest injury, what is the most important guide for the decision to operate?

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The hemodynamic status of the patient. Hemothorax after blunt injury is most often caused by nonoperative lesions of the lung and chest wall. In stable patients, therefore, evacuation of the hemothorax (with a chest tube); reexpansion of the lung, and correction of coagulopathy, hypothermia, and acidosis should be the initial focus. Chest tube output is helpful but is not the principal consideration.

3. What is a tension pneumothorax?

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Air in the pleural space under pressure caused by a one-way valve mechanism. This can be a life-threatening condition because the increase in intrathoracic pressure decreases venous return, which impaires right ventricular filling, resulting in a decrease in cardiac output.

4. What are the clinical signs of tension pneumothorax?

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Hypotension, tachycardia, absent breath sounds on the involved side, and distended neck veins. If the patient is doing badly and a tension pneumothorax is suspected, the chest should be decompresed without waiting for a radiograph.

5. How are patients with tension pneumothorax treated?

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For prehospital care, needle decompression should be done at the fifth intercostal space in the midaxillary line (never the midclavicular line). In the hospital, however, an experienced physician can completely decompress the pleural space just as rapidly with a tube thoracostomy.

6. Does it matter how many ribs are broken?

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Yes. Six or more fractures indicate a higher risk of pain induced hypoventilation with resultant pneumonia and acute respiratory distress syndrome (ARDS), particularly in elderly patients.

7. What is a flail chest?

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When multiple ribs are fractured in two or more places, the chest wall moves paradoxically (flails) with respiration.

8. How does flail chest impact ventilation?

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In spontaneously breathing patients, the portion of the thoracic cage that has lost bony continuity retracts inward during inspiration. This paradoxical motion (exacerbated by excruciating pain) impairs ventilation.

9. Do all patients with a flail segment require positive pressure ventilation to avoid hypoventilation?

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No. The impact of a flail segment on ventilation is not always profound, and with good analgesia, many patients can maintain their own work of breathing. Standard indications for intubation should be used.

10. Does flail chest affect oxygenation?

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Flail chest per se has little direct impact on oxygenation. However, virtually all patients with flail chest have an underlying pulmonary contusion. The severity of the pulmonary contusion is a more important determinant of outcome and need for intubation than the impaired mechanics of the chest wall. The pathophysiology of blunt injury to the chest with severe bony injury should be thought of as a single process (i.e., flail chest/pulmonary contusion).

11. What is the natural history of pulmonary contusion?

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Similar to other tissues, the lung undergoes shearing of parenchyma and rupture of small blood vessels (bruise) after a direct thump or rapid deceleration. This tissue injury is followed by edema. Thus, patients with pulmonary contusion typically deteriorate in the first 48 hours. Be careful because the initial chest radiograph may appear deceptively benign.

12. What is the most common initial presentation of blunt injury to the thoracic aorta?

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Death in the field. Eighty-five percent of patients with a torn thoracic aorta die of exsanguination before they reach the hospital. Disruption of the heart and great vessels is second only to head injury as a cause of death attributable to blunt trauma.

13. Of patients surviving to reach the hospital, what is the most common injury to the thoracic aorta?

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A tear across the intima and media just distal to the takeoff of the left subclavian artery. Because the adventitia is intact, the patient does not immediately exsanguinate, and if the lesion is detected promptly and surgically treated, the survival rate is 85%.

14. What are the clinical signs of a torn thoracic aorta?

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There are no definitive signs. Suspicion must be based on the mechanism of injury (i.e., rapid deceleration). The unusual physical signs associated with aortic disruption include upper extremity hypertension; unequal upper extremity pressures; loss of lower extremity pulses; and expanding hematoma in the root of the neck, which is extremely serious.

15. What findings on chest radiograph are associated with rupture of the descending thoracic aorta?

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Similar to the physical signs in this condition, no initial radiographic signs are definitive; however, watch for an indistinct aortic knob, widened mediastinum (> 8 cm at the level of the aortic knob), apical cap, left pleural effusion, depression of the left mainstem bronchus, rightward displacement of the esophagus (look for and follow the nasogastric tube), first-rib fractures, displacement of the trachea, and loss of the aortopulmonary window. A total of 15% of patients with a torn aorta have a normal mediastinum by radiograph, and 7% have a completely normal chest radiograph.

16. In the stable patient with a major mechanism of injury or chest radiographs consistent with aortic injury, how is the diagnosis made?

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Dynamic helical computed tomography of the chest approaches 100% sensitivity for detecting aortic injury; it is widely available and applicable to all stable patients. The definitive test remains aortography because it more precisely identifies the site (ascending or descending aorta) and extent of injury.

17. How does one identify the patient with a myocardial contusion?

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Only two things happen to the bruised heart: arrhythmia and pump failure. By far, the most common manifestation of blunt cardiac injury is arrhythmia. Studies confirm that patients with an initial electrocardiogram (ECG) that is normal have an exceedingly small chance of developing clinically significant arrhythmias during their hospital course. Any ECG abnormality is an indication for admission and 24 hours of cardiac monitoring. Hemodynamic compromise from blunt cardiac injury is unusual and not subtle; echocardiography should be used in patients with evidence of impaired contractility. Cardiac enzymes are poor predictors of arrhythmia or pump failure and are not recommended.
KEY POINTS: CHARACTERISTICS OF BLUNT CARDIAC INJURY

1. Most common manifestation is arrhythmia, although pump failure can occur.
2. Diagnostic evaluation with ECG: if normal, no further work-up is needed; if abnormal, 24 hours of inpatient monitoring is required.
3. If any evidence of myocardial dysfunction is seen, an echocardiogram should be performed.
4. Although some controversy remains, the trauma literature suggests that cardiac enzyme levels are not useful.

18. Where do blunt injuries to a bronchus usually occur? How do they present?

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They usually occur within a few centimeters of the carina. The mainstem bronchi are splayed apart with severe anteroposterior compression of the chest. As the lungs are displaced laterally, the mainstem bronchi may tear near the site where they are fixed at the carina. The typical presentation is a massive air leak, failure to reexpand the lung (”dropped lung”), or both after tube thoracostomy.

19. What are the indications for emergency department thoracotomy after blunt chest injury?

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Emergency thoracotomy should be done in patients with cardiovascular collapse after arrival in the emergency department. The outcome, however, is typically dismal: fewer than 1% of patients survive neurologically intact.

20. What is traumatic asphyxia?

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Traumatic asphyxia is the result of a protracted crush injury to the upper torso or epigastrium. In such an injury, venous hypertension is transmitted to the valveless veins of the upper body. Patients present with altered sensorium, petechial hemorrhages, cyanosis, and edema of the upper body. Although its initial presentation can be dramatic, with supportive care, the outcome is usually good.

References
WEB SITES

1. http://www.east.org/tpg/chap8.pdf
2. http://www.east.org/tpg/chap2.pdf
3. http://www.acssurgery.com/abstracts/acs/acs0505.htm
4. http://www.acssurgery.com/abstracts/acs/acs0602.htm
5. http://www.surgery.ucsf.edu/eastbaytrauma/Protocols/ER20%20protocol%20pages/thoracic_aorta.htm
6. http://www.surgery.ucsf.edu/eastbaytrauma/Protocols/ER20%20protocol%20pages/bluntcardiac.htm

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