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Approach to the adult with metabolic acidosis

Michael Emmett, MD
Harold Szerlip, MD, FACP, FCCP, FASN, FNKF
Section Editor
Richard H Sterns, MD
Deputy Editor
John P Forman, MD, MSc


On a typical Western diet, approximately 15,000 mmol of carbon dioxide (which can generate carbonic acid as it combines with water) and 50 to 100 mEq of nonvolatile acid (mostly sulfuric acid derived from the metabolism of sulfur-containing amino acids) are produced each day. Acid-base balance is maintained by pulmonary and renal excretion of carbon dioxide and nonvolatile acid, respectively.

Renal excretion of acid involves the combination of hydrogen ions with urinary titratable acids, particularly phosphate (HPO42-  +  H+   —>   H2PO4-), and ammonia to form ammonium (NH3  +  H+   —>   NH4+) [1]. The latter is the primary adaptive response since ammonia production from the metabolism of glutamine can be appropriately increased in response to an acid load [2].

Acid-base balance is usually assessed in terms of the bicarbonate-carbon dioxide buffer system:

Dissolved CO2  +  H2O  <—>  H2CO3   <—>   HCO3-  +  H+

The ratio between these reactants can be expressed by the Henderson-Hasselbalch equation. By convention, the pKa of 6.10 is used when the dominator is the concentration of dissolved CO2, and this is proportional to the pCO2 (the actual concentration of the acid H2CO3 is very low):

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Literature review current through: Nov 2017. | This topic last updated: Jun 30, 2017.
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