What is lung subcutaneous crepitus a sign of?

Subcutaneous Crepitus as a Sign of Pneumothorax or Pneumomediastinum

Lung subcutaneous crepitus (subcutaneous emphysema) is most commonly a sign of air leakage from the respiratory tract into soft tissues, typically indicating pneumothorax, pneumomediastinum, or both, which require prompt medical evaluation and intervention.

Pathophysiology and Causes

Subcutaneous emphysema occurs when air escapes from the respiratory system into surrounding tissues, creating a characteristic crackling sensation (crepitus) when palpated. The most common causes include:

1. Pneumothorax - Air leaks from damaged lung tissue into the pleural space and subsequently into subcutaneous tissues

2. Pneumomediastinum - Air in the mediastinum that dissects along fascial planes into subcutaneous tissues

3. Iatrogenic causes:

   • Chest tube complications (poor placement, tube blockage, side-port migration) 1
   • Mechanical ventilation with high airway pressures
   • Post-surgical complications

4. Traumatic causes:

   • Blunt or penetrating chest trauma
   • Rib fractures with lung parenchymal injury

5. Infectious causes:

   • Necrotizing infections (rare but serious)
   • Gas-forming organisms in soft tissues

Clinical Presentation

Subcutaneous emphysema typically presents with:

• Palpable crepitus (crackling sensation) under the skin
• Swelling of affected areas (commonly neck, chest wall, face)
• May be associated with dyspnea, chest pain, or voice changes
• Can range from mild and localized to extensive and widespread

Diagnostic Approach

1. Physical examination:

   • Palpation for characteristic crackling sensation
   • Assessment of respiratory status and hemodynamic stability

2. Imaging:

   • Chest radiograph: Shows radiolucent streaks in soft tissues and may reveal underlying pneumothorax
   • CT scan: Most sensitive for detecting small amounts of air and determining the source 2
   • Ultrasound: Can detect subcutaneous air at bedside and is useful for rapid assessment 3

Red Flags Requiring Immediate Action

• Extensive subcutaneous emphysema with respiratory distress
• Rapidly expanding subcutaneous emphysema
• Subcutaneous emphysema with systemic toxicity (may indicate necrotizing infection) 3
• Soft tissue crepitus with signs of sepsis (particularly in immunocompromised patients) 3

Management

Management depends on the underlying cause:

1. For pneumothorax-related subcutaneous emphysema:

   • Chest tube placement (ensuring proper positioning and function)
   • Addressing tube-related issues such as blockage or displacement 1

2. For extensive subcutaneous emphysema:

   • Supportive care
   • In severe cases, subcutaneous incisions ("blow holes") may be needed to release trapped air
   • Treating the underlying cause (e.g., fixing air leak)

3. For infectious causes:

   • Broad-spectrum antibiotics covering aerobic and anaerobic organisms
   • Urgent surgical debridement if necrotizing infection is suspected 3

Prognosis

The prognosis depends on the underlying cause:

• Most cases of non-infectious subcutaneous emphysema resolve with appropriate treatment of the underlying cause
• Extensive subcutaneous emphysema is associated with longer hospital stays and increased mortality 1
• Infectious causes, particularly necrotizing fasciitis, carry high mortality rates without prompt intervention

Clinical Pearls

• The presence of subcutaneous emphysema should always prompt investigation for an underlying pneumothorax or pneumomediastinum
• Not all subcutaneous emphysema represents life-threatening infection; clinical context is crucial 4
• Patients with minimal pain, no significant inflammatory changes, and stable vital signs can sometimes be managed conservatively with close monitoring 4
• Subcutaneous emphysema can spread rapidly along fascial planes, potentially causing airway compromise in severe cases

Remember that while subcutaneous emphysema itself is not typically life-threatening, it often signals an underlying condition that may require urgent intervention.