What are the pathophysiology and clinical presentation of a traumatic tension pneumothorax?

Traumatic Tension Pneumothorax: Pathophysiology and Clinical Presentation

Pathophysiology

Tension pneumothorax occurs when intrapleural pressure exceeds atmospheric pressure throughout the entire respiratory cycle due to a one-way valve mechanism that allows air to enter the pleural space during inspiration but prevents its escape during expiration, creating progressive pressure buildup that impairs venous return, reduces cardiac output, and causes cardiovascular collapse. 1, 2

The Valve Mechanism

• Air is drawn into the pleural space during inspiration when intrathoracic pressure becomes negative 1
• The one-way valve prevents air from exiting during expiration, causing progressive accumulation 1, 2
• This creates a pressure gradient where pleural pressure continuously rises with each respiratory cycle 2
• The mechanism causes mediastinal shift away from the affected side, kinking of great vessels, and reduced venous return leading to obstructive shock 2, 3

Critical Pathophysiologic Principle

• Tension development is NOT dependent on pneumothorax size—even small pneumothoraces can become immediately life-threatening 1, 2
• The clinical scenario of tension pneumothorax may correlate poorly with chest radiographic findings 1

Traumatic Causes

• Open chest wounds from penetrating trauma (stab wounds, gunshot wounds, blast injuries) create direct communication between the external environment and pleural space 1, 2
• High-velocity rifle wounds, shotgun wounds, and blast injuries create larger chest wall defects with greater risk of tension development 1
• Massive blunt chest trauma causes lung parenchymal injury with air leak into the pleural space 2
• Mechanical ventilation with positive pressure can convert a simple pneumothorax into tension pneumothorax by exacerbating the air leak 2, 3

Clinical Presentation

The diagnosis is purely clinical—never delay treatment for radiographic confirmation as this is immediately life-threatening. 2

Cardinal Signs

• Rapid labored respiration with progressive respiratory distress is the key presenting feature 1, 2
• The patient rapidly becomes distressed with cyanosis, profuse sweating, and tachycardia 1
• Progressive difficulty breathing that worsens over time distinguishes this from simple pneumothorax 1

Physical Examination Findings

• Attenuated or absent breath sounds on the affected side is the most common clinical manifestation 1
• Elevated chest wall on the side of injury compared with the contralateral side 1
• Subcutaneous emphysema and jugular venous distension 1
• Hypotension and shock induced by tachycardia and shortness of breath 1
• Loss of consciousness and absence of radial artery pulse are associated with high mortality 1

Important Clinical Caveat

• Tracheal deviation is NOT a reliable sign—it was not observed in any cases in the Israel Defense Forces trauma database of 111 tension pneumothorax cases 1
• It is very difficult to identify attenuated breath sounds through physical examination in noisy environments like battlefields 1

High-Risk Scenarios

• Patients on mechanical ventilation or non-invasive ventilation who suddenly deteriorate or develop pulseless electrical activity (PEA) arrest should be presumed to have tension pneumothorax 1, 2
• This diagnosis is frequently missed in the ICU setting 1
• Positive pressure ventilation changes the dynamics by exacerbating air leaks and accelerating tension development 3

Hemodynamic Deterioration

• Sudden deterioration in cardiopulmonary status related to impaired venous return, reduced cardiac output, and hypoxemia 1
• The mediastinal shift causes kinking of great vessels, further compromising venous return 2
• This progresses to obstructive shock and cardiovascular collapse if untreated 3