Why is loss / damage to the lipoprotein layer lining the alveoli fatal?

Surfactant: I believe that you are referring to something called the surfactant layer. Surfactant is composed of lipoproteins. Alveoli are the tiny structures shaped like bubbles which are the location of oxygen exchange in the lungs. Without them, we cannot oxygenate our blood. A layer of this surfactant is critical in keeping these tiny "bubbles" from collapsing in on themselves.