>>12222330In the simplest terms, your whole body gets inflamed. Inflamation is the reaction of your immune system to foreign stuff, be that bacteria, damaged cells, or other contaminants. When white blood cells detect any of these, they release molecules that let blood vessels relax, and thus lower blood pressure and as a consequence blood may not reach the tissues of organs such as the kidney, heart, lungs, brain, and liver.
However, Each of those organs also have systems that let them compensate for this lack of pressure. They release molecules that make the blood vessels that come into them contract tightly in order to raise the pressure locally and let the blood reach them. There's a point in which the lower blood pressure from systemic circulation can't get into these higher pressure local vessels, and the tissues start dying. There is another effect which is water from the tissue can't go back to the general circulation since the space between the cells has lower pressure than the veins it's supposed to go into, this is called Edema.
When Edema happens in the lungs, it's more difficult for air to go through the membrane that lets it dissolve into the bloodflow, since this membrane becomes thicker with water. Not only this makes it harder for oxygen to get in but harder for CO2 to get out, and thus blood becomes more acidic, cell function diminishes from protein denaturation and they die from lack of oxygen.
All the pieces of dead cells from tissues return into the blood flow, where again white blood cells recognizes them as threats and releases another bunch of vasodilators, the cycle runs again until all vital organ function ceases.
