Pyruvic acid enters the mitochondria where in the presence of oxygen it is converted into acetyl coenzyme A. Acetyl coenzyme A joins the Krebs cycle in which it is broken down to carbon dioxide, water and energy which is used to produce ATP. ATP is a complex organic molecule.
It is necessary to have an IV that is near isotonic with blood so that the concentration of multiple different molecules in our blood does not change. If it's not isotonic then the cells begin to contract because they are starting to lose water.
