This checklist relates to a systematic assessment of acid-base disturbances according to the physiologic approach.

 

  1. Acidosis / alkalosis?
  • pH < 7.38 and HCO3 < 22 mmol/L: metabolic acidosis
  • pH < 7.38 and pCO2 > 5.7 kPa: respiratory acidosis
  • pH > 7.42 and HCO3 > 26 mmol/L: metabolic alkalosis
  • pH > 7.42 and pCO2 < 5 kPa: respiratory alkalosis

 

  1. Compensation?
  • Respiratory compensation in the setting of metabolic acidosis: ∆ pCO2 = ∆ HCO3 x 0.16
  • Respiratory compensation in the setting of metabolic alkalosis: ∆ pCO2 = ∆ HCO3 x 0.09
  • Metabolic compensation in the setting of > 5 day-long respiratory acidosis: ∆ HCO3 = ∆ pCO2 x 2.62
  • Metabolic compensation in the setting of > 5 day-long respiratory alkalosis: ∆ HCO3 = ∆ pCO2 x 3.0

 

  1. Ions?
  • Calculate the anion gap (Na – Cl – HCO3); expected anion gap: 12 mmol/L if elderly, 6 mmol/L if young.
  • Calculate the delta gap (actual anion gap – expected anion gap)
  • Add the delta gap to the HCO3. A sum > 26 mmol/L suggests the presence of a metabolic alkalosis. A sum < 22 mmol/L suggests a hyperchloremic metabolic acidosis

 

  1. Diagnoses?
  • Speculate on the most plausible causes of the acid-base disorders using all available clinical information