Indication oand importance of extracorporeal support in the era of protective ventilation - my credo

VILI relies to variables as strain, stress and mechanical energy instead of tidal volume/kg ideal body weight and airway pressures (plateau and PEEP). In fact the actual distortion of the lung is measured by the strain: for the same tidal volume/kg the strain may be completely different depending on the "baby lung" size. Analogously the same airway pressure may result in extremely variable transpulmonary pressures (stress), depending on the relationship between lung and chest wall elastances. The initial trigger of stress and strain, however, is the force applied to the extracellular matrix times its displacement, which equals the product of pressure times delta-volume (PdV). The cyclic energy loads, applied at a given frequency (power), triggers the VILI, which may be seen, in this context, as a sort of "fatigue" of the extracellular matrix, analogous to the material "fatigue". We believe that the energy/power concept, which encompasses stress, strain and frequency allows to explain the different effects of tidal volume (dynamic), PEEP (static) and the physical thresholds conditioning the VILI appearance. The impressive diffusion of ECMO led to the great improvement of this technology, and there are increasing numbers of reports describing simple forms of extracorporeal support, primarily aiming at CO2 removal. The actual indications for ECMO depend on the patient’s need and the physician’s request. The choice of the technique may vary from low flow bypass with CO2 removal to high flow ECMO with total oxygenation support. If the aim is the treatment of life threatening hypoxemia, the clear cut indication is high flow veno-venous ECMO. If the patient, however, presents severe cardiac failure, veno-arterial ECMO must be used.