Updated: 2/13/2018

Acid-Base Nomogram

Review Topic

  • Simple acid-base disorders have changes in 
    • pH
    • PCO2
    • HCO3
  • The acid-base nomogram depicts these associated changes
    • for example, in metabolic acidosis there is a decreased pH and HCO3 level, along with a decreased PCO2 (due to respiratory compensation)
  • General principles
    • simple metabolic disorders (e.g., acidosis or alkalosis) have one set of expected values
      • this is because respiratory compensation is immediate
    • simple respiratory disorders (e.g., acidosis or alkalosis) have two set of expected values
      • renal compensation has not occured in acute respiratory disorders
        • renal compensation takes time to occur
      • renal compensation has occured in chronic respiratory disorders
        • blood pH would be expected to be close to normal or normal
Acid-Base Disorders
Acid-Base Disorder pH PCO2 [HCO3-] Compensatory Response
Metabolic acidosis
  • ↓ (primary disturbance)
  • Hyperventilation
Metabolic alkalosis 
  • ↑ (primary disturbance)
  • Hypoventilation
Respiratory acidosis
  • ↑ (primary disturbance)
  • ↑ renal HCO3- reabsorption
Respiratory alkalosis
  • ↓ (primary disturbance)
  • ↓ renal HCO3- reabsorption

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