Acid–Base and Electrolytes
Acid–base assessment and biochemical corrections in critically ill patients.
🧪 Corrected Anion Gap
Δ/Δ (Delta–Delta)
🧂 Corrected Electrolytes
Corrected Sodium
Corrected Calcium
Table 2: Expected compensation in acid–base disorders
| Metabolic acidosis | |
|---|---|
| For every decrease of 1 mEq/L in [HCO3-] (from 25 mEq/L), pCO2 should decrease by 0.85–1.2 mmHg (from 40 mmHg). | |
| Metabolic alkalosis | |
| For every increase of 1 mEq/L in [HCO3-] (from 25 mEq/L), pCO2 should increase by 0.7 mmHg (from 40 mmHg). | |
| Respiratory acidosis | |
| For every increase of 10 mmHg in pCO2 (from 40 mmHg), [HCO3-] increases by 1 mEq/L (from 25 mEq/L) if acute, or 3 mEq/L if chronic. | |
| Respiratory alkalosis | |
| For every decrease of 10 mmHg in pCO2 (from 40 mmHg), [HCO3-] decreases by 2–2.5 mEq/L (from 25 mEq/L) if acute, or 5 mEq/L if chronic. |
Clinical basis of acid–base assessment in the ICU
Acid–base evaluation is a fundamental tool in the Intensive Care Unit (ICU), allowing identification of metabolic and respiratory disorders, assessment of compensatory mechanisms and detection of potentially severe mixed disturbances.
Corrected anion gap
The anion gap (AG) helps estimate the presence of unmeasured plasma anions and is central to the evaluation of metabolic acidosis. Correction for albumin is essential because hypoalbuminemia, common in critically ill patients, may mask an elevated anion gap.
Delta–delta (Δ/Δ)
The Δ/Δ analysis compares the change in anion gap with the fall in bicarbonate, helping identify mixed metabolic disorders. It is especially useful to detect concomitant metabolic alkalosis or an additional metabolic acidosis.
Corrected sodium and calcium
Correction of sodium in hyperglycemia prevents underestimation of true natremia. Likewise, albumin-corrected calcium offers a better estimate of ionized calcium when protein abnormalities are present.
Clinical warning
This tool is intended for educational and clinical support purposes only. It does not replace medical judgment, clinical guidelines or institutional protocols.