ICU · Renal / acid-base

Mixed Acid–Base Disorders & the Delta–Delta — The 5-Step Approach

Also known as Mixed acid-base disorder · Delta-delta · Delta ratio · Anion gap · Winter formula · Compensation · Salicylate toxicity · DKA plus vomiting · Henderson-Hasselbalch · Strong ion difference · Stewart approach · Triple disorder

A mixed acid-base disorder is the presence of two or more primary acid-base disturbances simultaneously. The body NEVER over-compensates — if the compensation is more or less than expected, a second primary disorder is present. The systematic approach: (1) the pH to the acidosis or the alkalosis; (2) the pCO2 and the bicarbonate to the primary; (3) the expected compensation (the Winter formula for the metabolic acidosis: the expected pCO2 equals 1.5 times bicarbonate plus 8 plus-or-minus 2; the Henderson-Hasselbalch equation pH equals 6.1 plus log of bicarbonate over 0.03 times pCO2); (4) the anion gap (the Na minus (Cl plus bicarbonate), 8 to 12, the albumin-corrected — the AG rises 2.5 per 10 g/L fall in the albumin); (5) the delta-delta (the delta AG over the delta bicarbonate: about 1 the pure high-AG acidosis, under 1 the concurrent normal-gap hyperchloraemic acidosis, over 2 the concurrent metabolic alkalosis). The Stewart (strong ion difference) approach: pH is set by the PaCO2, the strong ion difference (the Na minus Cl, about 40), and the total weak acids (the albumin). The mixed metabolic acidosis (the combined high-AG and the normal-AG — the delta ratio under 1). The mixed metabolic alkalosis and acidosis (the delta ratio over 2). The triple disorders (the metabolic alkalosis plus the metabolic acidosis plus the respiratory alkalosis — the classic in the sepsis with the vomiting plus the lactic acidosis plus the hyperventilation). The salicylate toxicity (the respiratory alkalosis plus the high-AG acidosis).