So is this something being deployed in the COVID battle do you know? Or something that's maybe done for the young ones with a better chance?
I do not know much about critical care, but it's something that, when available, it's used to replace lung and heart function. A ventilator forces air into your lungs, so it replaces/supports the breathing function (the mechanical effort our muscles do) and also allows high concentrations of O2, up to 100%, to be delivered (this can also be done with an O2 mask, but in those the patient breathes normally and out of his own effort) at optimum pressure.
Now if the exchange of gases between lung and blood is compromised (damage to the alveolar membrane, lungs filled with fluid) the oxygenation of the blood doesn't happen anyway, even if you can pump air into the lungs (breathing). Pumping air into the lungs is also useless if the heart can't pump the blood throughout the body. Here enters this complex system of extra-corporeal oxygenation of the blood as a possible last resort. It only makes sense to use it if the loss of lung function (oxygenation, not breathing) or heart function is expected to be reversible, so it won't save someone with terminal heart failure, etc.
It can, where available, be used when this level of artificial life support is required to keep someone alive whilst the underlying causes are corrected. So it can be used in Covid-19, as in many other situations.