In the strong ion approach to acid-base status, pH, partial pressure of carbon dioxide (respiratory component) and strong ions (metabolic component) are independent variables, whereas bicarbonate is a dependent variable. Strong ions include sodium (cation), chloride (anion), phosphate (anion), protein (particularly albumin; considered anions) and unmeasured ions (XA). Cations are thought of as bases and anions as acids, therefore increases in cations (high sodium) causes an alkalosis whereas increases in anions (chloride, phosphate, proteins, unmeasured anions) causes an acidosis. Similarly, decreased cations causes an acidosis and decreased anions (proteins, primarily) causes an alkalosis.
