Diaphragmatic Assessment in the Intensive Care Unit

Importance of Diaphragmatic Assessment and Ultrasound Techniques

Diaphragmatic ultrasound assessment is a useful and feasible bedside tool that should be considered a basic skill for intensivists, particularly for evaluating diaphragmatic function in patients being weaned from mechanical ventilation 1, 2
Diaphragmatic excursion is recommended as a basic skill for intensivists to assess diaphragmatic function, particularly in patients being weaned from mechanical ventilation 1, 2

Transdiaphragmatic pressure (Pdi) requires simultaneous recordings of esophageal pressure (Pes) and gastric pressure (Pga) 3, 4
Pdi is obtained by measuring the differential pressure between these two signals 4
The ratio of inspiratory Pga swings to Pdi helps assess diaphragmatic contribution to tidal effort 4
A negative Pga/Pdi ratio indicates severe diaphragmatic dysfunction or paralysis 4
Maximum Pdi (Pdi,max) can estimate diaphragm strength but has a wide normal range 4

Diaphragmatic dysfunction is a major cause of weaning failure 5, 3
Maximum relaxation rate of respiratory muscles slows during weaning failure, suggesting respiratory muscle fatigue 5
Phrenic nerve stimulation with twitch measurements is an appealing method to monitor diaphragmatic contractility, independent of patient effort 5

Minimizing tidal Pdi has been proposed as a target for titrating pressure support ventilation 4
Diaphragmatic electromyography via esophageal electrode can quantify crural diaphragm activity and examine precise timing of activation 5

Incorrect placement of the gastric balloon in the lower esophagus can mimic severe diaphragmatic dysfunction when measuring Pga/Pdi ratio 4
Recruitment of abdominal muscles during expiration followed by sudden relaxation at inspiration can also mimic diaphragmatic dysfunction 4

Magnetic stimulation of phrenic nerves has advantages over electrical stimulation and may increase the feasibility of twitch stimulation in ICU settings 5