Pulmonary Shunt Fraction (Qs/Qt)

Pulmonary Shunt Fraction (Qs/Qt) | 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

The Pulmonary Shunt Fraction (Qs/Qt) calculator estimates the proportion of blood bypassing effective pulmonary gas exchange from hemoglobin, arterial blood gas, oxygen saturation, inspired oxygen, and optional mixed-venous values. It calculates PAO₂ with the alveolar gas equation and reports Qs/Qt, oxygen contents, and a shunt category. This tool is for education and clinical reference, not medical advice.

When to use

Estimate pulmonary shunt fraction from arterial blood gas and oxygenation data.
Assess oxygenation during a room-air estimate or a 100%-oxygen shunt test.
Review how hemoglobin, arterial saturation, and mixed-venous values affect oxygen content and Qs/Qt.

How it works

1Enter hemoglobin, PaO₂, SaO₂, PaCO₂, and FiO₂; FiO₂ defaults to 1.0.
2The calculator derives alveolar oxygen pressure using PAO₂ = FiO₂ × (Patm − 47) − PaCO₂/0.8, with atmospheric pressure defaulting to 760 mmHg.
3It calculates capillary, arterial, and venous oxygen content using the provided values.
4It applies Qs/Qt = (CcO₂ − CaO₂)/(CcO₂ − CvO₂) and returns the fraction, percentage, category, and whether mixed-venous defaults were used.

Use cases

Critical care review of hypoxemia and suspected pulmonary shunt.
Respiratory physiology teaching using arterial and mixed-venous oxygen content.
Comparison of room-air estimates with values from a 100%-oxygen shunt test.

Examples

1. Room-air oxygenation estimate

Clinician or respiratory physiology learner

Background

A patient has hemoglobin of 13.5 g/dL and arterial blood gas values of PaO₂ 100 mmHg, SaO₂ 0.97, and PaCO₂ 40 mmHg.

Problem

Estimate Qs/Qt when mixed-venous oxygen values are unavailable.

How to use

Enter hemoglobin 13.5, PaO₂ 100, SaO₂ 0.97, PaCO₂ 40, and FiO₂ 0.21. Leave PvO₂ and SvO₂ blank.

Patm 760 mmHg; default PvO₂ 40 mmHg; default SvO₂ 0.75.

Outcome

The calculator derives PAO₂ of about 99.73 mmHg and reports Qs/Qt of about 0.12, or 11.5%, categorized as a mild shunt. The result uses default mixed-venous values and a room-air estimate.

2. 100%-oxygen shunt test estimate

Critical care clinician

Background

A patient receiving FiO₂ 1.0 has hemoglobin of 12 g/dL, PaO₂ 110 mmHg, SaO₂ 0.98, and PaCO₂ 40 mmHg. Mixed-venous values are available.

Problem

Estimate the shunt fraction using measured PvO₂ and SvO₂ rather than default venous values.

How to use

Enter hemoglobin 12, PaO₂ 110, SaO₂ 0.98, PaCO₂ 40, FiO₂ 1.0, PvO₂ 35, and SvO₂ 0.70.

FAQ

What inputs are required?

Hemoglobin, PaO₂, SaO₂, PaCO₂, and FiO₂ are required. Patm, PvO₂, and SvO₂ are optional.

What happens if PvO₂ or SvO₂ is missing?

The calculator uses PvO₂ of 40 mmHg and SvO₂ of 0.75, and identifies the venous source as default values.

What FiO₂ should I enter for a 100%-oxygen shunt test?

Enter 1.0. For a room-air estimate, enter 0.21.

What does a Qs/Qt above 20% indicate?

It is categorized as a severe shunt in this calculator. Interpret the result with the clinical context.

Is this calculator medical advice?

No. It provides an estimate for education and clinical reference and does not replace professional assessment.

Patm 760 mmHg.

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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. Room-air oxygenation estimate

2. 100%-oxygen shunt test estimate

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