Determination of Ka of Isolated Plasma and Whole Blood of Critically Ill Patients With Sepsis, Non-septic Patients and Healthy Volunteers: an International, In-vitro Acid-base Study.

Acid-base equilibrium has been object of study for more than 100 years in medicine because of its relevance in patients' management and in determining their prognosis, especially in the ICU.

A concept closely related to acid-base equilibrium is that of "buffer", term used to define any substance able to limit the changes in pH caused by the addition or loss of alkali or acid.

Depending on its physiochemical features, every buffer has one or more pH (negative logarithm of hydrogen ion concentration) values where its ability to keep pH stable is maximal. These values are defined as Ka or semi equivalence points, i.e. the pH values where the buffer dissolved in solution is half in its associated form (AH) and half in its dissociated form (A-).

Several studies tried to determine the normal values of both concentration and Ka of ATOT. However, they did not lead to univocal results. Moreover, many of these values come from studies of veterinary medicine or are the result of theoretical estimates on human plasma.

Staempfli and Constable performed a single experimental study on human plasma in 2003. These authors, however, analyzed only isolated plasma, neglecting whole blood, and computed ATOT and Ka values of healthy volunteers, while Ka and ATOT values for critically ill patients with sepsis are still unknown.