What are the recommendations for dedicated Point-of-Care Ultrasound (POCUS) diaphragm assessment and management of diaphragm dysfunction?

Point-of-Care Ultrasound (POCUS) for Diaphragm Assessment

Diaphragmatic excursion assessment using POCUS should be considered a basic skill for clinicians evaluating diaphragmatic function, particularly in patients being weaned from mechanical ventilation. 1

Technical Approach to Diaphragm POCUS

Patient Positioning

• Position patient in semi-recumbent position (30-45°) for optimal imaging
• For excursion assessment: right lateral decubitus position provides better visualization

Probe Selection and Placement

• For diaphragmatic excursion:

  • Use low-frequency curvilinear probe (2-5 MHz)
  • Position at right subcostal margin between mid-clavicular and anterior axillary lines
  • Aim probe medially, cephalad and dorsally to visualize the posterior third of the diaphragm
  • Use M-mode to measure craniocaudal displacement during respiration

• For diaphragm thickness and thickening fraction:

  • Use high-frequency linear probe (7-12 MHz)
  • Position at zone of apposition (8th-10th intercostal space) at mid-axillary line
  • Identify diaphragm as three-layered structure between pleural and peritoneal lines
  • Measure thickness at end-expiration and end-inspiration

Measurements and Interpretation

1. Diaphragmatic Excursion (DE):

   • Normal values during quiet breathing: 1.0-2.5 cm
   • Normal values during deep breathing: >2.5 cm
   • Abnormal: <1.0 cm suggests dysfunction
   • Paradoxical movement (upward during inspiration) indicates paralysis

2. Diaphragm Thickness:

   • Normal end-expiratory thickness: 0.15-0.30 cm
   • Thickness <0.2 cm suggests atrophy

3. Thickening Fraction (TF):

   • Calculate using: TF = [(End-inspiratory thickness - End-expiratory thickness)/End-expiratory thickness] × 100%
   • Normal TF: >30-36%
   • TF <20% suggests dysfunction
   • TF <30% predicts weaning failure 2

Clinical Applications

Weaning from Mechanical Ventilation

• Diaphragmatic excursion >10-14 mm predicts successful extubation 2
• Thickening fraction >30-36% predicts successful extubation 2
• Serial measurements can track recovery of diaphragm function

Diagnosis of Diaphragm Dysfunction

• Qualitative assessment: Look for paradoxical or absent movement
• Quantitative assessment: Measure excursion and thickening fraction
• Compare bilateral measurements to detect unilateral dysfunction

Monitoring Diaphragm Atrophy

• Serial thickness measurements can detect progressive atrophy during mechanical ventilation
• Decrease in thickness >10% suggests significant atrophy

Assessing Respiratory Workload

• Thickening fraction correlates with respiratory muscle workload during assisted ventilation 2
• Can guide ventilator adjustments to optimize diaphragm loading

Advantages of Diaphragm POCUS

• Non-invasive and radiation-free
• Highly reproducible with proper technique
• Provides real-time assessment at bedside
• Can be repeated serially to monitor progress
• Concordant with fluoroscopic findings 1

Limitations and Pitfalls

• Technical challenges:

  • Left hemidiaphragm visualization more difficult (34.7% success rate vs. 98.7% for right) 3
  • Obesity and subcutaneous emphysema limit image quality
  • Incorrect probe placement can miss the zone of apposition

• Interpretation challenges:

  • Wide range of normal values for measurements
  • Abdominal muscle recruitment can falsely suggest diaphragmatic dysfunction 4
  • Influence of patient positioning and respiratory effort on measurements

Recommended Imaging Algorithm for Suspected Diaphragm Dysfunction

1. Initial imaging: Chest radiography 1

   • Evaluate for relative position of diaphragm and effect on lung volumes

2. Secondary evaluation:

   • POCUS for diaphragmatic excursion assessment 1
   • Consider fluoroscopy for confirmation if POCUS findings are equivocal 1

3. Advanced imaging (if needed):

   • CT chest without IV contrast for structural assessment 1
   • Consider CT with IV contrast if underlying etiology requires vascular evaluation 1

Training Recommendations

The European Society of Intensive Care Medicine recommends that estimation of diaphragmatic excursion should be considered a basic ultrasound skill for intensivists 1, 4, particularly for assessing diaphragmatic function in patients being weaned from mechanical ventilation.

While diaphragmatic excursion assessment is recommended as a basic skill, the evaluation of diaphragmatic thickening fraction requires more advanced training due to its technical complexity 1.