title: Theorethical principles of fluid managment according to physicochemical Stewart approach.
abstract: Interpreting acid base disturbances according to the physicochemical Stewart approach allows the cause of such abnormalities to be discovered. This method is based on three independent variables: SID (strong ion difference), mainly sodium and chloride; weak acids concentration - Atot, mainly albumins and phosphate; and carbon dioxide tension - pCO₂. These three independent variables are responsible for the change of water dissociation and for the change in H+ concentration and, consequently, the change in serum pH value. The SID value of the fluids administered to a patient is responsible for the change of serum SID value and therefore causes a change in the patient's acid base status. During the infusion of a given fluid, the SID value of the serum becomes closer to the SID value of that fluid; on the other hand, the infusion causes a decrease in Atot concentration. In order to avoid acid base disturbances connected with fluid administration, the SID value of fluids being administered should be greater than 0 and lower then the serum SID. It has been suggested that fluids should be given of which the SID value is as close as possible to the actual serum HCO₃ concentration. Knowing the SID value of the fluid administered, and the serum HCO₃ concentration, one can expect a change of serum pH after a fluid infusion. Administering a fluid with a SID greater than the HCO₃ concentration causes a pH increase towards alkalosis. Likewise, administering a a fluid with a SID lower than the HCO₃ concentration causes a pH decrease towards acidosis. It seems that knowledge of the electrolyte concentration and the SID value of an administered fluid is an important factor regarding acid base disturbances.
authors.affiliation: Department of Anaesthesiology, Intensive Therapy and Pain Management University Hospital No.2 in Poznan, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Smuszkiewicz
authors.forename: Jakub
authors.initials: J
authors.lastname: Szrama
mesh_terms: D000136:Acid-Base Equilibrium; D000137:Acid-Base Imbalance / Q000628:therapy; D005440:Fluid Therapy; D006801:Humans; D006863:Hydrogen-Ion Concentration