Physiology of Chest Tube Drainage
Core Physiological Principle
A chest tube functions by restoring the normal negative intrapleural pressure (–8 cm H₂O during inspiration, –3.4 cm H₂O during expiration) that allows the lung to fully expand against the chest wall by evacuating abnormal air or fluid collections from the pleural space. 1, 2, 3
Mechanism of Action
The chest tube creates a controlled pathway for drainage that:
- Removes accumulated air, blood, or fluid that disrupts the normal pressure gradient between the pleural space and atmosphere 2, 3, 4
- Re-establishes the physiologic negative pressure within the pleural cavity that is essential for lung expansion 2, 3
- Prevents tension physiology by providing continuous egress for ongoing air leaks or fluid accumulation 5
The tube must remain patent to function—clogging occurs in up to 36-40% of cases, particularly with blood products, which can lead to retained collections causing tamponade, hemothorax, or inflammatory complications 1
Drainage System Mechanics
Water Seal vs. Suction
- Water seal drainage relies on gravity and the patient's own respiratory mechanics to generate the pressure gradient for evacuation 1, 6
- Normal physiologic pressures are sufficient for most pneumothoraces and effusions without additional suction 1
- Suction should NOT be applied immediately after tube insertion but can be added after 48 hours if the lung fails to re-expand or air leak persists 1
- High-volume, low-pressure systems (–10 to –20 cm H₂O) are recommended when suction is needed, as high-pressure systems can cause air stealing, hypoxemia, or perpetuate air leaks 1
Critical Safety Consideration
A bubbling chest tube should NEVER be clamped—this can convert a simple pneumothorax into life-threatening tension pneumothorax by preventing air egress while the leak continues 7. Even non-bubbling tubes should generally not be clamped 7.
Tube Size and Placement Physiology
- Small-bore tubes (10-14F) are as effective as large-bore tubes (20-24F) for most pneumothoraces and effusions, with success rates of 84-97% 1, 5
- Larger tubes may be needed only when air leak volume exceeds small tube capacity or when thick fluid/blood is present 1
- Optimal placement at the 4th-5th intercostal space in the mid- or anterior-axillary line ensures proper anatomic positioning for drainage 2, 3
Patency Maintenance Physiology
Maintaining tube patency without breaking the sterile field is essential to prevent retained blood complications that trigger inflammatory cascades, including postoperative atrial fibrillation and effusions 1.
What NOT to Do
- Stripping or milking tubes is NOT recommended—this creates dangerously high negative pressure that can cause tissue trauma, hemorrhage, or disruption of vascular structures 1, 7
- Breaking the sterile field to manually clear obstructions significantly increases infection risk and should be avoided 1, 7
Appropriate Interventions
- Flushing with 20-50 mL normal saline can confirm patency when output slows 7
- Active clearance systems that maintain patency without breaking sterility show promise in reducing retained blood complications 1
Timeline of Physiologic Resolution
- Median time to pneumothorax resolution is 8 days (19 days with underlying lung disease) 1, 7
- Persistent air leak beyond 48 hours warrants specialist referral for complex drain management decisions 1, 7
- Tubes can be removed once the pneumothorax has completely resolved on chest radiograph, air leak has ceased, and repeat imaging 5-12 hours later confirms no reaccumulation 1
Common Pitfalls
- Applying suction too early, especially in pneumothoraces present for several days, can precipitate re-expansion pulmonary edema 1
- Inadequate drainage leads to retained collections that cause mechanical complications (tamponade, hemothorax) and inflammatory sequelae (effusions, atrial fibrillation) 1
- Premature tube removal before confirming complete resolution and cessation of air leak risks recurrence 1