18. Goligher EC, Dres M, Patel BK, Sahetya SK, Beitler JR, Telias I, et al. Lung and

Diaphragmatic dysfunction is more frequently unilateral than bilateral. It must also be borne in mind that the le hemidiaphragm is more challenging to assess than the right hemidiaphragm [12]. Using new soware and an anatomical motional (M)-mode for the ultrasound evaluation of diaphragmatic excursion, Pasero et al. were able to identify a greater proportion of patients exhibiting le diaphragm dysfunction following cardiac surgery [13]. e soware used permits the free rotation to the M-mode line even if the acoustic window is not favourable for the good alignment of the ultrasound beam for le hemidiaphragmatic movements. An alternative solution, in the case of drainages and dressings inhibiting an anterior approach, would be the lateral approach as described by Lerolle et al. [14]. ese authors found a linear correlation between excursion evaluated by ultrasound and the trans­diaphragmatic pressure gradient – an expression of the contribution of the diaphragm to the maximal inspiratory effort. Furthermore, Pierre-Henri Moury et al. recently assessed weaning from mechanical ventilation in cardiac surgical patients by evaluating diaphragm thickening during the spontaneous breathing trial (SBT) at the zone of apposition [15]. e authors found that diaphragm thickening could be markedly reduced in postoperative cardiac surgery, with 75% of patients found to have a thickening fraction (TF) less than 20%. is incidence was higher compared with those published by previous studies (reporting incidences around 60%). Diaphragmatic dysfunction in the study by Pierre-Henri Moury and colleagues mainly implied difficulty in weaning from invasive mechanical ventilation in the immediate postoperative period, and the authors did not correlate their data with respect to mechanical ventilation weaning failure.

As explained above, interventions within the upper thoracic region (for example, thymoma surgery) can cause damage to the phrenic nerve, and thus lead to diaphragm dysfunction. Cases of thymoma are frequently associated with neuromuscular disorders, such as myasthenia gravis, which may also involve the diaphragm [20]. Similarly, the use of muscle relaxants or corticosteroids in the case of a patient with some form of muscular asthenia can precipitate a borderline condition of compensated diaphragmatic dysfunction [21]. LoMauro et al. found diaphragm dysfunction to be common following bi-pulmonary transplant surgery, even in clinically silent forms or with subclinical manifestations [22].

In thoracic surgery, POCUS is proven to be a sufficiently reliable tool for establishing the presence and degree of postoperative diaphragmatic dysfunction. Diaphragmatic excursion and the thickening fraction correlate linearly with the forced vital capacity [19].

Since Stephen Hales’s first observations on the diaphragm’s functioning kinetics in the early 18th century, this organ’s role on the hemodynamics of the systemic circulation and the thoracic and abdominal organs has been clear [29, 30]. e pressure gradient created by the movement variation promotes the flow of venous blood to the heart from the liver, and from the abdominal compartment to the inferior vena cava. Rabinovici and colleagues were among the first to observe in animal models an alternating fluctuation of the caval flow during the respiratory cycle [31].