Lactate refers to a negatively charged organic molecule that must be pared with a positively charged cation. It is common for doctors and other heath care professionals who were not trained in basic chemistry to misunderstand this. We can have lactic acid which is lactate plus a proton or H+, We can also have the lactate base, an anion pared with an inert cation such as a Na+ (Sodium ion). Sodium lactate is a basic substance whereas lactic acid is an acid. The ratio of lactic acid to lactate base is in equilibrium based on the pH but there is no “free” or unpaired lactate anywhere in the universe. When the pH is low there will be more lactic acid than lactate base in the blood or another solution. We don’t need evidence based medicine to test this hypothesis. An understanding of acid base chemistry is all that is needed.
The total lactate base plus lactic acid is discussed and reported in clinical medicine as simply lactate which creates confusion. The unqualified term lactate is ambiguous and frequently misinterpreted. It is true that total lactate(base plus acid) is generally higher when anaerobic metabolism is producing lactic acid and proceeding faster than it is metabolized. If total lactate (base plus acid) is measured and found to be higher than normal this is probably reflective of anaerobic metabolism proceeding apace. Thus, the total lactate reported to doctors, nurses and other health care professionals is a convenient substitute for the actual amount of lactic acid that has accumulated as a result of anaerobic metabolism. The level of lactic acid itself can be determined only if the pH is known. Since generally we don’t know the pH the total lactate is used as a substitute. There is nothing wrong with this simplified, practical but theoretically incorrect narrative as long as doctors, nurses and other health care professionals do as they are told (follow the protocols) and don’t try to think for themselves. They have to follow guidelines, protocols, recipes whatever it is called and not try to modify them. Their knowledge is flawed so using it becomes improper. The science that states that high lactate(total unqualified) represents the degree of metabolic acidosis and therefor the severity of shock or sepsis is practical but theoretically incorrect. It will do fine if one does not think about it.
As a practical approach the theoretically correct parameter, lactic acid isn’t used. Total lactate is used. Since it works most of the time, it is a practical if not the scientifically correct approach. As it is easier and most importantly cheaper it has been adopted.