Lactic Acid and Base Deficit in Trauma Patients

Lactic acid is a byproduct of anaerobic metabolism (Metabolism without oxygen). Normally, the cells use anaerobic metabolism and it breaks down the glucose to form energy. Normally, the cells use oxygen available to breakdown the glucose and produce ATP. This occurs when you have oxygen. If the body does not have the oxygen, it then converts the metabolism to an anaerobic metabolism. The end product is lactic acid. If the body is acidic, and the pH drops, this means that there is a tissue ischemia. If we take the glucose (CCCCCC), and break it down, you will have two pyruvates—each attached to a CCC. That’s not a lot of energy and the pyruvate is a mild acid.

There are different ways to get more energy, such as going to the mitochondria to use the oxygen and produce more ATP. When we break down the glucose to produce energy in the presence of oxygen, so the glucose will split into two separate three carbon molecules called the pyruvate and produces ATP. If you don’t have oxygen, then the pyruvate will be attached to hydrogen atoms, which is H+ (proton that is an acid). If you are acidotic and a sick patient, you will have a lot of floating hydrogen atoms and a lot of floating protons.

The pyruvate will attach to the free hydrogen protons. The H+ pyruvate is called lactic acid. It is a pyruvate that is holding onto hydrogen. The lactic acid is the end product of anaerobic metabolism.

Now, with a base deficit, as the number of protons goes up, which is hydrogen, then the pH will go down and the patient will become acidotic. The body uses bicarbonate as a buffer if the pH goes down. There are a lot of protons within the body and the bicarbonate will be exhausted in this situation. The bicarbonate goes down because we are combining it with the protons. When the bicarbonate goes down, this becomes metabolic acidosis.

When you combine the bicarbonate with the protons, this will make carbonic acid (H₂CO₃), rather than HCO₃^-, which is bicarbonate. The carbonic acid can give water (H₂O), and CO₂. The lactic acid will give out the protons and be buffered by the bicarbonate, leaving lactic acid. When this occurs, the bicarbonate will go down, and this will be the base deficit.

When checking if a patient has been resuscitated, you can check in several ways

The two ways this is asked on exams:

1. Base deficit from -2 to +2
2. Serum lactate level (normal is less than 2.5, some sources use normal less than 2)