What is the Henderson-Hasselbalch equation and how does it explain the pathophysiology of metabolic acidosis?

Updated: Oct 05, 2018
  • Author: Antonia Quinn, DO; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Answer

The Henderson-Hasselbalch equation describes the relationship between blood pH and the components of the H2 CO3 buffering system. This qualitative description of acid/base physiology allows the metabolic component to be separated from the respiratory components of acid/base balance.

pH = 6.1 + log (HCO3/ H2 CO3)

Bicarbonate (HCO3) is in equilibrium with the metabolic components.

  • Bicarbonate production in the kidney

  • Acid production from endogenous or exogenous sources

Carbonic acid (H2 CO3) is in equilibrium with the respiratory component, as shown by the below equation:

H2 CO3 = PCO2 (mm Hg) X 0.03

Metabolic acidosis can be caused by the following:

  • Increase in the generation of H+ from endogenous (eg, lactate, ketones) or exogenous acids (eg, salicylate, ethylene glycol, methanol)

  • Inability of the kidneys to excrete the hydrogen from dietary protein intake (type I, IV renal tubular acidosis)

  • The loss of bicarbonate (HCO3) due to wasting through the kidney (type II renal tubular acidosis) or the gastrointestinal tract (diarrhea)

  • The kidneys' response to a respiratory alkalosis


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