Diaphragm Ultrasound in Cardiac Surgery: State of the Art

Abstract

In cardiac surgery, patients are at risk of phrenic nerve injury, which leads to diaphragm dysfunction and acute respiratory failure. Diaphragm dysfunction (DD) is relatively frequent in cardiac surgery and particularly affects patients after coronary artery bypass graft. The onset of DD affects patients' prognosis in term of weaning from mechanical ventilation and hospital length of stay. The authors present a narrative review about diaphragm physiology, techniques used to assess diaphragm function, and the clinical application of diaphragm ultrasound in patients undergoing cardiac surgery.

Keywords: cardiac ICU; cardiac surgery; diaphragm ultrasound; phrenic nerve.

Figure 1

Right diaphragm ultrasound. Note the normal inspiratory motion (64 mm) of the hemidiaphragm from the subcostal view. After the visualization of the right hemidiaphragm (bright line) using a B-mode (image on the left), an M mode was applied (image on the right) to record diaphragm motion.

Figure 2

Measurement of the right peak sniff tissue Doppler imaging velocity from the subcostal view. The diaphragm velocity was recorded during a sniff maneuver. Here is a reduced peak sniff velocity (7 cm/s) in a patient with muscular dystrophy.

Figure 3

Measurement of the right diaphragm thickness (dotted line) in the end-expiratory phase (A) and end-inspiratory phase (B), using ultrasound. The diaphragm is visualized as a hypo-echogenic central layer surrounded by two hyper-echogenic lines, namely, the pleural line and the peritoneum.

Figure 4

Chest X ray in a post-operative patient with diaphragm paralysis. Note ascension of the left diaphragm.