Oxygenation Index Calculator

Oxygenation Index Calculator for Critical Care. For an eligible invasively ventilated PARDS assessment at least four hours after diagnosis, PALICC-2 places OI 4 to below 16 in the mild/moderate group and OI at least 16 in the severe group. Below four is below this oxygenation criterion, not proof of normal lungs.

For shared guidance on choosing a tool and documenting results, read the clinical calculator workflow.

How this calculator works

Oxygenation index is 100 multiplied by inspired oxygen fraction and mean airway pressure, divided by arterial oxygen tension. Mean airway pressure is a ventilator measurement in cmH2O, not mean arterial pressure. The unit selector converts oxygen percent to fraction and accepts PaO2 in mmHg or kPa.

When to use this calculator

Use the numerical result to understand oxygenation during invasive ventilation. Classification of pediatric acute respiratory distress syndrome also requires the full PALICC-2 diagnostic criteria and its timing requirements. This page does not determine whether those prerequisites are met.

Inputs used

  • Inspired oxygen (fraction)
  • Mean airway pressure (not arterial pressure) (cmH2O)
  • Arterial oxygen tension (mmHg)

Clinical interpretation

For an eligible invasively ventilated PARDS assessment at least four hours after diagnosis, PALICC-2 places OI 4 to below 16 in the mild/moderate group and OI at least 16 in the severe group. Below four is below this oxygenation criterion, not proof of normal lungs.

Worked example

With FiO2 80%, mean airway pressure 18 cmH2O and PaO2 60 mmHg, OI is 100 x 0.8 x 18 / 60 = 24. At PaO2 90 the index is exactly 16; at 360 it is 4. These examples do not independently diagnose PARDS.

Limitations and safety notes

FiO2 must be between 0.21 and 1 after conversion, with positive finite airway pressure and PaO2. Ventilator settings and timing influence the result. The tool does not select inhaled nitric oxide, high-frequency ventilation or extracorporeal support from an index alone.

Frequently asked questions

Is OI 16 moderate?

Under the cited PALICC-2 framework it meets the severe oxygenation boundary, provided the diagnosis, timing and invasive-ventilation prerequisites are satisfied.

Which pressure is entered?

Mean airway pressure from the ventilator, not systemic mean arterial pressure.

Can I enter FiO2 as 80?

Yes only with the percent unit selected; the fraction input for the same concentration is 0.8.

References

  • PALICC-2 primary consensus, invasive OI thresholds4 and16 and severity timing at least4h; current direct PMC open challenged, source details rechecked by primary indexed results. https://pmc.ncbi.nlm.nih.gov/articles/PMC9848214/

Editorial review and citation methodology

Maintained by the Quick Medical Calculator Editorial Team. Content record date: September 9, 2026. A content date is not evidence of independent clinical review. Individual clinical sign-off is not recorded on this page.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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