pneumonia is a build-up of fluids and/or pus in the lungs due to inflammation of the lungs. The inflammation could come from the immune system attacking a pathogen. Ventilators allow oxygen exchange to continue in areas of the lungs that can still function. The studies that are saying that ventilators are killing COVID-19 patients are not necessarily considering that someone has to be really sick to be put on a ventilator. Did the ventilator kill them or did their disease?