Acid-Base

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

2. 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

3. 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

4. Diagnoses?

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