# Base Excess Calculator (Metabolic Component)

Calculate base excess (BE) using the Siggaard-Andersen formula. BE < −3 metabolic acidosis, > +3 metabolic alkalosis. HCO₃⁻ auto-calculated from pH + PaCO₂ if omitted. Derived from Siggaard-Andersen 1974, Cornell PICU, Medscape, and Langer 2022. Not medical advice.

> Canonical page: https://elysiatools.com/en/tools/base-excess-calculator

- **Category:** Health

- **Keywords:** base excess, base deficit, standard base excess, siggaard andersen, metabolic acidosis, metabolic alkalosis, acid base, blood gas, abg, bicarbonate, henderson hasselbalch, critical care

## Overview

The Base Excess Calculator estimates the metabolic component of an acid-base disturbance from arterial pH, PaCO₂, and optional measured HCO₃⁻. It uses the Siggaard-Andersen formula, classifies the result as metabolic acidosis, normal, or metabolic alkalosis, and can calculate HCO₃⁻ from pH and PaCO₂ when HCO₃⁻ is omitted. This tool is not medical advice.

## Inputs

- **pH** (number): Arterial blood pH.
- **PaCO₂ (mmHg)** (number): Arterial CO₂ partial pressure (mmHg).
- **HCO₃⁻ (mmol/L, optional)** (number): Measured bicarbonate (mmol/L). If omitted, calculated from Henderson-Hasselbalch.
- **Decimal Places** (number)

## When to use

- Assess the metabolic component of an arterial blood gas result.
- Estimate base deficit or base excess when pH, PaCO₂, and HCO₃⁻ are available.
- Calculate HCO₃⁻ from pH and PaCO₂ when a measured bicarbonate value is not provided.

## How it works

- Enter the arterial blood pH and PaCO₂ in mmHg.
- Optionally enter measured HCO₃⁻ in mmol/L; if omitted, the calculator derives it using the Henderson-Hasselbalch relationship.
- The calculator applies BE = 0.9287 × (HCO₃⁻ − 24.4 + 14.83 × (pH − 7.4)).
- The JSON result reports base excess, standard base excess, metabolic classification, severity, and calculation details.

## Use cases

- Reviewing arterial blood gas results in critical care and emergency settings.
- Quantifying metabolic acidosis or base deficit in patients with shock or trauma.
- Checking whether an acid-base disturbance has a normal, acidotic, or alkalotic metabolic component.

## Frequently asked questions

### What does base excess measure?

Base excess estimates the metabolic component of an acid-base disturbance, separate from the respiratory component.

### What does a negative BE indicate?

A BE below −3 generally indicates metabolic acidosis or a base deficit.

### What does a positive BE indicate?

A BE above +3 generally indicates metabolic alkalosis.

### Is HCO₃⁻ required?

No. Entered HCO₃⁻ is optional; when omitted, it is calculated from pH and PaCO₂.

### What units does the calculator use?

PaCO₂ is entered in mmHg, while HCO₃⁻ and base excess are reported in mmol/L.

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