What does a diaphragm excursion of less than 2 cm, as assessed by percussion during a physical exam, indicate?

Diaphragm Excursion <2 cm on Percussion: Clinical Significance

A diaphragm excursion of less than 2 cm measured by percussion is an unreliable finding that should not be used to guide clinical decision-making, as percussion has poor correlation with actual diaphragmatic movement and should be replaced by ultrasound or fluoroscopy for accurate assessment of diaphragmatic dysfunction. 1

Why Percussion is Inadequate

The traditional teaching that diaphragm excursion <2 cm by percussion indicates dysfunction is fundamentally flawed:

• Percussion demonstrates wide interobserver variation and poor correlation with actual diaphragmatic excursion measured radiographically 1
• Percussion missed paradoxical movement in patients where it was present, failing to detect severe diaphragmatic dysfunction 1
• Five patients with reduced forced vital capacity had clinically measured diaphragm movement >2 cm by percussion, demonstrating that normal percussion findings do not exclude significant respiratory impairment 1
• Percussion should no longer be recommended as part of the physical examination for estimating diaphragmatic movement due to its limited clinical value 1

What the Finding May Suggest (Despite Poor Reliability)

If percussion suggests reduced excursion, consider it a prompt for further investigation rather than a diagnostic finding:

• Potential diaphragmatic dysfunction or paralysis, which occurs in up to 60% of critically ill patients with respiratory failure 2
• Neuromuscular disorders affecting the diaphragm, particularly in postoperative patients who show higher incidence 2
• Severe respiratory muscle weakness that may contribute to weaning failure from mechanical ventilation 3, 4

Appropriate Diagnostic Approach

Replace percussion with validated imaging modalities:

First-Line: Ultrasound

• Diaphragmatic ultrasound is recommended as a basic skill for assessing diaphragmatic function, particularly in patients being weaned from mechanical ventilation 5, 3, 4
• Ultrasound findings correlate with fluoroscopic imaging with reproducible results and high sensitivity/specificity for neuromuscular disorders 5
• Normal diaphragmatic excursion by ultrasound ranges up to 6.0 cm during maximal inspiration, with a linear relationship between excursion and tidal volume 6
• Excursion <1.37 cm by ultrasound may predict poor response to non-invasive ventilation 2

Alternative: Fluoroscopy

• Fluoroscopy provides more accurate assessment of diaphragmatic motion compared to static chest radiography 5
• Chest radiography can provide clues to diaphragm paralysis but is less accurate than fluoroscopy 5

Advanced: Transdiaphragmatic Pressure Measurement

• A negative gastric pressure to transdiaphragmatic pressure ratio indicates severe diaphragmatic dysfunction or phrenic nerve dysfunction 5, 3, 4
• This measurement requires simultaneous esophageal and gastric pressure recordings and is typically reserved for ICU settings 5, 4

Critical Pitfalls to Avoid

• Do not rely on percussion alone to diagnose or exclude diaphragmatic dysfunction, as it has been definitively shown to be unreliable 1
• Do not assume normal percussion findings exclude significant respiratory impairment, as patients with reduced pulmonary function can have apparently normal percussion findings 1
• When using ultrasound, ensure proper technique to avoid mimicking diaphragmatic dysfunction through incorrect probe placement or misinterpretation of abdominal muscle recruitment 5, 3, 4