Alveolar Oxygen Tension Calculator

Calculates alveolar oxygen tension using the alveolar gas equation. Includes field guidance, formula provenance, interpretation and Learn More content.

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Alveolar Oxygen Tension
Clinical Decision Tool

Calculates alveolar oxygen tension using the alveolar gas equation.

Enter FiO₂ as a fraction, for example 0.21 for room air.
Use local barometric pressure; 760 mmHg is standard sea-level pressure.
Use an arterial blood gas value measured in mmHg.
Use 0.8 when no measured value is available and that assumption is clinically appropriate.
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Clinical Decision Support Only

MediCalc calculators are intended to support qualified healthcare professionals and must not replace professional clinical judgement. Do not enter patient-identifiable information into Saved Progress.

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Learn More About Alveolar Oxygen Tension
MedicalC Knowledge Hub

Alveolar Oxygen Tension: Clinical Guide

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Calculates alveolar oxygen tension using the alveolar gas equation.

Overview

Calculates alveolar oxygen tension using the alveolar gas equation.

Clinical Significance

Estimates alveolar oxygen tension for gas-exchange assessment. Interpretation depends on inspired oxygen, altitude, ventilation and the paired arterial oxygen tension.

How It Is Calculated

  • PAO₂ = FiO₂ × (PB − 47) − PaCO₂/RQ.

Interpretation

  • Estimates alveolar oxygen tension for gas-exchange assessment. Interpretation depends on inspired oxygen, altitude, ventilation and the paired arterial oxygen tension.

Worked Example

Enter a clinically consistent set of values in the displayed units. MedicalC applies: PAO₂ = FiO₂ × (PB − 47) − PaCO₂/RQ.

Limitations

  • This tool does not establish a diagnosis or mandate treatment.
  • Published cut-offs may vary between cohorts and measurement methods.
  • Calculation precision cannot compensate for poor source data.

Clinical Pearls

  • Trend the result over time where clinically appropriate.
  • Record the source values and units alongside the calculated result.

Common Mistakes

  • Using the wrong unit.
  • Combining measurements obtained at different times.
  • Applying a research-derived threshold as a universal treatment trigger.

Frequently Asked Questions

What does this calculator provide?

Calculates alveolar oxygen tension using the alveolar gas equation.

Can this result be used alone?

No. It must be interpreted with clinical context and appropriate investigations.

What equation is used?

PAO₂ = FiO₂ × (PB − 47) − PaCO₂/RQ.

What is the main limitation?

The result depends on valid inputs and may not be calibrated for every population or setting.

References

  1. West JB. Respiratory Physiology: The Essentials. Wolters Kluwer. — Formula, physiological or validation reference.

Reviewed by: MedicalC Clinical Editorial Team
Last reviewed: July 2026

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Reviewed by: MedicalC Clinical Editorial Team Last reviewed: July 2026

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Clinical Disclaimer

MedicalC calculators and clinical tools are intended to support healthcare professionals. They do not replace clinical judgement, individual patient assessment, local guidance or specialist advice.

Results should always be interpreted in the context of the patient’s history, examination, investigations, current clinical condition and applicable professional guidance.

Reviewed by: MedicalC Clinical Editorial Team Last reviewed: July 2026
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