Stewart Calculator — Strong Ion / Physicochemical Acid-Base Analysis

Blood gas

Required

pH Arterial sample, 37 °C

PaCO₂ Partial pressure of carbon dioxide

mmHg

HCO₃⁻ Leave blank to derive from pH and PaCO₂

mmol/L

Weak acids

A_TOT

Albumin Dominant non-volatile weak acid

g/dL

Phosphate Inorganic PO₄, optional

mg/dL

Strong ions

Required

Strong cations

Na⁺ ★ Sodium

mmol/L

K⁺ Potassium, optional

mmol/L

iCa²⁺ Ionized calcium, optional

mmol/L

Mg²⁺ Magnesium, optional

mmol/L

Strong anions

Cl⁻ ★ Chloride

mmol/L

Lactate ★ Plasma lactate

mmol/L

Interpretation

Results appear as you enter required values. All calculations update live.

Disclaimer This tool implements the simplified Fencl-Stewart and Figge-Fencl formulations of the physicochemical acid-base model. It is intended to assist, not replace, clinical judgment. Results depend on the accuracy of the entered values and the assumptions of the Stewart framework, which remain debated. Always interpret alongside the full clinical picture, the traditional base-excess analysis, and institutional reference ranges. Do not enter patient identifiers. This tool performs all calculations in the browser and stores no data.