What is the best way to measure a pneumothorax (collapsed lung)?

The Best Way to Measure a Pneumothorax

Lung ultrasound is the best method to measure a pneumothorax as it more accurately rules in and rules out pneumothorax compared to chest radiography, with higher sensitivity and specificity. 1

Diagnostic Methods for Pneumothorax

Lung Ultrasound (Preferred Method)

Lung ultrasound offers significant advantages for pneumothorax detection:

• Superior accuracy: More accurately rules in and rules out pneumothorax than supine anterior chest radiography (strong recommendation, level A evidence) 1
• Higher sensitivity: Multiple studies show sensitivity of 79-85.7% for ultrasound versus 31.8-71.4% for chest X-ray 2, 3
• Excellent specificity: 95-100% specificity, comparable to chest X-ray 2, 3
• Point-of-care advantage: Can be performed at bedside during resuscitation, avoiding risky patient transfers 3

Key Sonographic Signs for Pneumothorax Diagnosis 1:

1. Absence of lung sliding - Normal rhythmic movement between parietal and visceral pleura is absent
2. Absence of B-lines - Their presence would exclude pneumothorax at that point
3. Absence of lung pulse - No subtle rhythmic movement with cardiac oscillations
4. Presence of lung point - The transition point where absent sliding meets normal sliding, representing the boundary of the pneumothorax

In emergency situations, absence of pleural line movement (sliding or pulse) coupled with absence of B-lines allows prompt diagnosis without searching for the lung point 1.

Chest Radiography

While still commonly used, chest radiography has limitations:

• Lower sensitivity: Only 31.8-62.9% sensitive for detecting pneumothorax 2, 3
• Good specificity: Nearly 100% specific when positive 2, 3
• Technical considerations: Debate exists regarding inspiratory versus expiratory views 4
• Positioning matters: Supine radiographs are particularly limited for pneumothorax detection 1

CT Scan

• Gold standard: Highest accuracy but with limitations
• Not first-line: Should be reserved for cases where pneumothorax requires additional evaluation to look for underlying causes 1
• Resource intensive: Requires patient transport, higher radiation, more time and cost

Measuring Pneumothorax Size

For determining pneumothorax size, which affects management decisions:

• Lung point detection: Bedside ultrasound can differentiate between small and large pneumothorax by identifying the lung point location 1
• Mapping technique: The physical limit of pneumothorax can be mapped on the chest wall by identifying where absent sliding transitions to normal sliding 1

Clinical Implementation Algorithm

1. Initial assessment: Use lung ultrasound as first-line imaging for suspected pneumothorax

2. Diagnostic sequence:

   • Check for lung sliding (absence suggests pneumothorax)
   • If no sliding, look for B-lines (presence excludes pneumothorax)
   • If no B-lines, check for lung pulse (presence excludes pneumothorax)
   • Identify lung point to confirm diagnosis and estimate size

3. When to use chest X-ray:

   • Documentation purposes
   • When ultrasound expertise is unavailable
   • For monitoring known pneumothorax over time

4. When to use CT:

   • When ultrasound and X-ray findings are equivocal
   • To evaluate for underlying lung pathology
   • When precise measurement is needed for research purposes

Common Pitfalls and Caveats

• False positives in ultrasound: Lung bullae, contusions, and adhesions can mimic pneumothorax findings 1
• Learning curve: While some debate exists about the learning curve for lung ultrasound, the technique is considered basic with a steep learning curve 1
• Technical limitations: Subcutaneous emphysema can limit ultrasound visualization
• Patient factors: Severe obesity or extensive chest wall injuries may reduce ultrasound accuracy

Lung ultrasound represents a significant advancement in pneumothorax detection and measurement, offering better diagnostic accuracy than traditional chest radiography while avoiding radiation exposure and patient transport risks.