How does adding suction in thoracostomy (chest tube insertion) help re-expand the lung?

How Suction in Thoracostomy Re-expands the Lung

Applying suction to a chest tube creates a negative pressure gradient that helps evacuate air from the pleural space, allowing the natural elastic recoil of the lung to re-expand the collapsed tissue and restore normal intrapleural pressure relationships.

Mechanism of Action

Suction works through several physiological mechanisms:

1. Pressure Gradient Creation:

   • Normal intrapleural pressures are approximately -8 cm H₂O during inspiration and -3.4 cm H₂O during expiration 1
   • Suction enhances this negative pressure, creating a stronger gradient that facilitates lung expansion

2. Air Evacuation:

   • Removes accumulated air from the pleural space more efficiently than water seal drainage alone
   • Helps overcome resistance in the drainage system, particularly when there's fluid in the tubing 2

3. Elastic Recoil Assistance:

   • Complements the natural elastic recoil properties of lung tissue
   • The negative pressure helps overcome any resistance to re-expansion

Optimal Suction Parameters

The BTS guidelines recommend specific parameters for effective suction:

• Timing: Suction should not be applied immediately after tube insertion but added after 48 hours for persistent air leak or failure of pneumothorax to re-expand 1
• Pressure Level: High volume, low pressure (-10 to -20 cm H₂O) suction systems are recommended 1
• Flow Volume: The system should have capacity to increase suction with an air flow volume of 15-20 L/min 1

Types of Suction Systems

Not all suction systems are equally effective:

• Recommended: High volume, low pressure systems (e.g., Vernon-Thompson pump or wall suction with pressure-reducing adaptor) 1
• Avoid: High pressure, high volume suction systems which can cause:
  • Air stealing
  • Hypoxemia
  • Perpetuation of persistent air leaks 1
• Also avoid: High pressure, low volume systems 1

Clinical Effectiveness

Research demonstrates the effectiveness of appropriate suction:

• In patients with penetrating chest trauma, continuous low pressure suction achieved full lung expansion in 92% of cases compared to 74% with water seal alone 3
• Suction significantly reduced time to chest tube removal (8.2 days vs. 12.6 days) 3
• Suction decreased hospital length of stay (7.2 days vs. 12.4 days) 3

Important Considerations and Pitfalls

1. Timing Concerns:

   • Applying suction too early after tube insertion can precipitate re-expansion pulmonary edema (RPO), especially in pneumothoraces present for several days 1
   • Suction should be initiated after 48 hours if there's persistent air leak or failure to re-expand 1

2. System Patency:

   • Fluid accumulation in drainage tubing can significantly reduce the actual negative pressure transmitted to the pleural space 2
   • With increasing fluid volume in tubing, pressure differential between system and patient can increase from 1.14 to 36.69 cm H₂O 2

3. Specialist Care Required:

   • Patients requiring suction should only be managed on lung units with specialist medical and nursing experience 1
   • Persistent air leaks or failure to re-expand after 48 hours should prompt referral to a respiratory physician 1

4. Surgical Referral Timing:

   • If suction fails to resolve the pneumothorax, surgical referral should be made at 5-7 days for those without pre-existing lung disease 1
   • Earlier referral (2-4 days) should be considered in those with underlying disease, large persistent air leak, or failure of lung to re-expand 1

By creating appropriate negative pressure in the pleural space, suction helps evacuate air and fluid, allowing the natural elastic properties of the lung to facilitate re-expansion while minimizing complications.