Acid-base disturbances in nephrotic syndrome: analysis using the CO 2 /HCO 3 method (traditional Boston model) and the physicochemical method (Stewart model).

BACKGROUND: The Stewart model for analyzing acid-base disturbances emphasizes serum albumin levels, which are ignored in the traditional Boston model. We compared data derived using the Stewart model to those using the Boston model in patients with nephrotic syndrome.

METHODS: Twenty-nine patients with nephrotic syndrome and six patients without urinary protein or acid-base disturbances provided blood and urine samples for analysis that included routine biochemical and arterial blood gas tests, plasma renin activity, and aldosterone. The total concentration of non-volatile weak acids (ATOT ), apparent strong ion difference (SIDa), effective strong ion difference (SIDe), and strong ion gap (SIG) were calculated according to the formulas of Agrafiotis in the Stewart model.

RESULTS: According to the Boston model, 25 of 29 patients (90%) had alkalemia. Eighteen patients had respiratory alkalosis, 11 had metabolic alkalosis, and 4 had both conditions. Only three patients had hyperreninemic hyperaldosteronism. The Stewart model demonstrated respiratory alkalosis based on decreased PaCO2 , metabolic alkalosis based on decreased ATOT , and metabolic acidosis based on decreased SIDa. We could diagnose metabolic alkalosis or acidosis with a normal anion gap after comparing delta ATOT [(14.09 - measured ATOT ) or (11.77 - 2.64 × Alb (g/dL))] and delta SIDa [(42.7 - measured SIDa) or (42.7 - (Na + K - Cl)]). We could also identify metabolic acidosis with an increased anion gap using SIG > 7.0 (SIG = 0.9463 × corrected anion gap-8.1956).

CONCLUSIONS: Patients with nephrotic syndrome had primary respiratory alkalosis, decreased ATOT due to hypoalbuminemia (power to metabolic alkalosis), and decreased levels of SIDa (power to metabolic acidosis). We could detect metabolic acidosis with an increased anion gap by calculating SIG. The Stewart model in combination with the Boston model facilitates the analysis of complex acid-base disturbances in nephrotic syndrome.