KEY POINTS

1. A significant acid-base abnormality often signals a sinister underlying problem.
2. All acid-base abnormalities result from alterations in the dissociation of water.
3. Only three factors independently affect acid-base balance: Pa_{CO 2} , SID, and A_TOT .
4. Respiratory acidosis and alkalosis are caused by hypercarbia and hypocarbia, respectively.
5. Metabolic acidosis is caused by decreased SID or increased A_TOT . Decreased SID results from accumulation of metabolic anions (i.e., shock, ketoacidosis, and renal failure), hyperchloremia, and free water excess. Increased A_TOT results from hyperphosphatemia.
6. Metabolic alkalosis is caused by increased SID or decreased A_TOT . The SID increases because of sodium gain, chloride loss, or free water deficit. A_TOT decreases in hypoalbuminemia and hypophosphatemia. This condition is particularly common in critical illness.
7. Most acid-base disorders are treated by reversal of the cause.