How is pneumothorax (collapsed lung) graded and treated based on its size and severity?

Pneumothorax Grading and Management

Pneumothorax is graded as "small" (<2 cm rim of air between lung margin and chest wall) or "large" (>2 cm rim), and treatment decisions are based primarily on symptoms and whether it is primary or secondary pneumothorax, not just size alone. 1

Size Classification

The British Thoracic Society classification divides pneumothorax into two categories based on the visible rim of air between the lung margin and chest wall on PA chest radiograph: 1

• Small pneumothorax: <2 cm rim of air 1
• Large pneumothorax: >2 cm rim of air 1

Important Caveats About Sizing

• Plain PA chest radiographs typically underestimate pneumothorax volume, so clinical judgment must supplement radiographic findings 1
• CT scanning is the most accurate method for exact size quantification but is only recommended for complex cases (bullous disease, surgical emphysema obscuring the radiograph, or differentiating pneumothorax from bullae) 1, 2
• Expiratory radiographs add little diagnostic value and are not routinely indicated 1
• If clinical suspicion is high but PA radiograph is normal, obtain lateral or lateral decubitus views, which can detect pneumothorax in up to 14% of additional cases 1

Treatment Algorithm: Primary Pneumothorax

Small Primary Pneumothorax (<2 cm) Without Breathlessness

• Observation alone is appropriate 1
• Consider discharge with early outpatient follow-up 1
• Provide clear written instructions to return immediately if breathlessness develops 1
• 70-80% of small pneumothoraces resolve without persistent air leak 1

Large Primary Pneumothorax (>2 cm) OR Any Size With Breathlessness

• Simple aspiration is first-line treatment 1
• If aspiration successful: admit for 24 hours observation 1
• If aspiration fails: proceed to intercostal chest drain 1
• Never leave breathless patients without intervention regardless of radiographic size 1

Treatment Algorithm: Secondary Pneumothorax

Small Secondary Pneumothorax (<1 cm or Isolated Apical) Without Symptoms

• Observation with hospitalization 1
• High-flow oxygen (10 L/min) to accelerate reabsorption (increases rate 4-fold) 1
• Use caution with oxygen in COPD patients 1

Small Secondary Pneumothorax (<2 cm) With Minimal Breathlessness

• Simple aspiration may be attempted only in patients <50 years old with minimal breathlessness 1
• Lower success rate than primary pneumothorax 1
• If aspiration fails: proceed to chest drain 1

All Other Secondary Pneumothoraces

• Intercostal chest drain is required 1
• Secondary pneumothoraces cause breathlessness out of proportion to size due to poor lung reserve 1
• Hospitalization is mandatory 1

Critical Clinical Pearls

Symptoms Trump Size

• Marked breathlessness with a small (<2 cm) primary pneumothorax may herald tension pneumothorax—intervene immediately 1
• Clinical symptoms are more severe in secondary pneumothorax and are not reliable indicators of actual size 1

Arterial Blood Gas Findings

• PaO2 <80 mmHg in 75% of pneumothorax patients 1
• In secondary pneumothorax, 16% have PaO2 <55 mmHg and PaCO2 >50 mmHg 1
• Underlying lung disease and pneumothorax size together predict degree of hypoxemia 1

Oxygen Therapy

• High-flow oxygen (10 L/min) increases pneumothorax reabsorption rate 4-fold 1
• Natural reabsorption rate is only 1.25-1.8% of hemithorax volume per 24 hours 1
• A 15% pneumothorax takes 8-12 days to resolve without oxygen supplementation 1

Special Populations

• In severe bullous lung disease, CT scanning prevents unnecessary and potentially dangerous aspiration attempts by differentiating bullae from pneumothorax 1
• Many patients delay seeking care for days (46% wait >2 days), which increases risk of re-expansion pulmonary edema 1

Common Pitfalls to Avoid

• Do not rely on pulmonary function tests—they are weakly sensitive for pneumothorax presence or size 1
• Do not routinely order expiratory films—they add minimal diagnostic value 1
• Do not discharge secondary pneumothorax patients for observation—they require hospitalization even for small pneumothoraces 1
• Do not assume small radiographic size means minimal clinical impact, especially in secondary pneumothorax 1