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Systematic acid-base interpretation is a core clinical reasoning skill used daily in acute care settings. A structured stepwise approach prevents diagnostic errors and guides targeted management in complex patients.
Acid-base physiology relies on the Henderson-Hasselbalch equation and the bicarbonate buffer system. The lungs regulate CO2 within minutes while the kidneys regulate bicarbonate over hours to days. Understanding expected compensation ranges — such as Winter's formula for metabolic acidosis (expected pCO2 = 1.5 × HCO3 + 8 ± 2) — is critical to identifying mixed disorders.
A reliable six-step approach: (1) assess pH, (2) identify primary disorder, (3) verify expected compensation, (4) calculate anion gap, (5) apply delta-delta ratio if anion gap is elevated, (6) interpret in clinical context. This framework is essential for recognizing mixed disorders such as a concurrent metabolic alkalosis masking a severe metabolic acidosis.