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Table 2 Diaphragm anatomy and physiology, and ventilator impact in diaphragm ultrasonography

From: EXpert consensus On Diaphragm UltraSonography in the critically ill (EXODUS): a Delphi consensus statement on the measurement of diaphragm ultrasound-derived parameters in a critical care setting

Anatomy and physiology

 

Anatomy

 Muscle

  No consensus was achieved on continuity of diaphragm thickness in the zone of apposition

  The significance of echogenicity is unknown but should be investigated

 Changes in thickness

  ≥ 10% decrease from baseline thickness is regarded as cut-off for clinically relevant atrophy

  No consensus was achieved regarding cut-off for increased thickness due to confounding with inflammation and oedema

 Limitations for measurements

  Obesity and large tidal volume can complicate measurements

Physiology

 Maximum effort measurements offer important information but are hard to obtain and compare due to subjectivity of a maximum effort

Dysfunction

 Diaphragm excursion < 2 cm is indicative of dysfunction during quiet breathing

 No consensus was achieved on cut-off for dysfunction based on thickening fraction

 

Ventilator impact

 

Excursion

 Positive pressure ventilation augments amplitude with greater lung inflation

 PEEP lowers diaphragm resting position and reduces excursion

Thickness

 Positive pressure ventilation reduces patient effort and as such thickness at end inspiration

 PEEP lowers the diaphragm resting position with higher thickness at end expiration due to shortening of the muscle

Thickening

 Positive pressure ventilation reduces patient effort and as such diaphragmatic thickening

 PEEP lowers the diaphragm resting position with higher thickness at end expiration due to shortening of the muscle and as such its percentual thickening