Nearly all biochemical reactions in the body are dependent on maintenance of a physiological hydro-gen ion concentration. The latter is tightly regulated because alterations in hydrogen ion concentration are associated with widespread organ dysfunction. This regulation—often referred to as acid–base balance—is of prime importance to anesthesiologists. Changes in ventilation and perfusion and the infusion of electrolyte-containing solutions are common dur-ing anesthesia and can rapidly alter acid–base balance.
Our understanding of acid–base balance is evolving. In the past, we focused on the concentrationof hydrogen ions [H+], CO2balance, and the baseexcess/deficit. We now understand that the strong ion difference (SID), Pco2, and totalweak acid concentration (ATOT) best explain acid– base balance in physiological systems.