What causes shortness of breath in flail chest?

Causes of Shortness of Breath in Flail Chest

Shortness of breath in flail chest is primarily caused by paradoxical movement of the chest wall, underlying pulmonary contusion, and mechanical instability leading to respiratory failure. 1, 2

Primary Mechanisms

1. Paradoxical Chest Wall Movement

• The hallmark of flail chest is paradoxical movement where the flail segment moves inward during inspiration and outward during expiration
• This paradoxical movement directly impairs normal respiratory mechanics by:
  • Reducing effective tidal volume
  • Increasing work of breathing
  • Causing inefficient ventilation 1, 2
• A paradoxical movement of 3-5 cm can cause severe respiratory and circulatory disorders and can quickly lead to death 1

2. Underlying Pulmonary Contusion

• Flail chest is frequently accompanied by pulmonary contusion (underlying lung injury)
• This combination significantly worsens respiratory function through:
  • Decreased lung compliance
  • Ventilation-perfusion mismatch
  • Impaired gas exchange 1, 3
• The World Society of Emergency Surgery (WSES) and Chest Wall Injury Society (CWIS) guidelines emphasize that pulmonary contusion often dictates the severity of respiratory compromise 1, 2

3. Pain and Splinting

• Severe pain from multiple rib fractures leads to:
  • Voluntary splinting (limited chest wall movement)
  • Shallow breathing
  • Ineffective cough
  • Retention of secretions 2
• This creates a cycle of worsening respiratory function and increased risk of pneumonia 4

Secondary Mechanisms

1. Mechanical Instability

• Loss of chest wall integrity affects the mechanics of breathing
• Inability to generate negative intrathoracic pressure needed for effective inspiration 1, 2
• Decreased functional residual capacity 3

2. Associated Complications

• Pneumothorax or hemothorax may coexist with flail chest, further compromising respiratory function 1
• Progressive atelectasis due to poor cough and secretion clearance 2
• Development of pneumonia (occurs in up to 21% of flail chest patients) 4

3. Systemic Response

• Increased oxygen consumption due to increased work of breathing
• Metabolic acidosis from respiratory insufficiency
• Shock in severe cases, further compromising tissue oxygenation 1

Clinical Implications

• Patients with flail chest typically present with:

  • Rapid breathing (tachypnea)
  • Visible paradoxical movement of chest wall
  • Decreased breath sounds
  • Signs of respiratory distress and hypoxemia 1

• Without proper management, flail chest can rapidly progress to respiratory failure requiring mechanical ventilation (59% of patients require ventilation with an average duration of 12.1 days) 4

Management Considerations

• Control paradoxical movement through:

  • Positive pressure ventilation in severe cases
  • Surgical stabilization of rib fractures (SSRF) in appropriate candidates 1, 2

• Adequate pain control is essential to improve respiratory mechanics:

  • Multimodal analgesia
  • Regional anesthesia techniques including epidural catheters 2, 4

• Maintain airway patency and adequate oxygenation:

  • Avoid fluid overload which can worsen pulmonary contusion
  • Consider non-invasive ventilation before progressing to intubation 2

The presence of both flail chest and pulmonary contusion significantly increases morbidity and mortality, requiring more aggressive management strategies than either condition alone 5.