Winter's Formula (Expected PaCO₂ in Metabolic Acidosis)

Winter's Formula (Expected PaCO₂ in Metabolic Acidosis) | Online Free Tool | Elysia Tools

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category: Health
Input types: number
Output type: json
Sample coverage: 4
API ready: Yes

Overview

Winter's Formula calculator estimates the expected PaCO₂ for respiratory compensation in metabolic acidosis using 1.5 × HCO₃⁻ + 8 ± 2 mmHg. Enter bicarbonate and optionally measured PaCO₂ to assess whether compensation is appropriate or whether a mixed respiratory disorder may be present. Not medical advice.

When to use

Estimate expected respiratory compensation when metabolic acidosis is present.
Compare a measured arterial PaCO₂ with the expected compensation range.
Screen for possible concomitant respiratory acidosis or respiratory alkalosis.

How it works

1Enter serum or arterial blood gas bicarbonate in mmol/L.
2The tool calculates expected PaCO₂ as 1.5 × HCO₃⁻ + 8 mmHg.
3It reports a range extending 2 mmHg above and below the expected value.
4If actual PaCO₂ is provided, the tool classifies compensation as appropriate, high, or low relative to that range.

Use cases

Rapid bedside review of arterial blood gas results in critical care.
Assessment of respiratory compensation in metabolic acidosis during nephrology evaluation.
Educational practice with bicarbonate and PaCO₂ values in acid-base medicine.

Examples

1. Appropriate respiratory compensation

Critical care clinician

Background

A patient with metabolic acidosis has an HCO₃⁻ of 10 mmol/L and a measured PaCO₂ of 24 mmHg.

Problem

Determine whether the measured PaCO₂ falls within the expected respiratory compensation range.

How to use

Enter HCO₃⁻ = 10 and actual PaCO₂ = 24, using 1 decimal place.

HCO₃⁻: 10 mmol/L; actual PaCO₂: 24 mmHg; decimal places: 1

Outcome

Expected PaCO₂ is 23 ± 2 mmHg, giving a range of 21–25 mmHg. The measured PaCO₂ of 24 indicates appropriate respiratory compensation.

2. Concomitant respiratory acidosis

Emergency physician

Background

A patient with metabolic acidosis has an HCO₃⁻ of 15 mmol/L and a measured PaCO₂ of 40 mmHg.

Problem

Check whether the measured PaCO₂ is higher than expected for compensation.

How to use

Enter HCO₃⁻ = 15 and actual PaCO₂ = 40, using 1 decimal place.

FAQ

What is Winter's Formula?

It estimates expected PaCO₂ during respiratory compensation for metabolic acidosis: 1.5 × HCO₃⁻ + 8 ± 2 mmHg.

What inputs does the calculator require?

HCO₃⁻ in mmol/L is required. Measured PaCO₂ in mmHg is optional.

What does an appropriate compensation result mean?

The measured PaCO₂ falls within 2 mmHg of the calculated expected value.

What does a higher-than-expected PaCO₂ suggest?

It may indicate concomitant respiratory acidosis alongside metabolic acidosis.

What does a lower-than-expected PaCO₂ suggest?

It may indicate concomitant respiratory alkalosis alongside metabolic acidosis.

HCO₃⁻: 15 mmol/L; actual PaCO₂: 40 mmHg; decimal places: 1

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Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Appropriate respiratory compensation

2. Concomitant respiratory acidosis

FAQ

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