Oxygenation Index (OI) Calculator
Calculate conventional Oxygenation Index from matched FiO₂, ventilator mean airway pressure, and arterial PaO₂ during invasive mechanical ventilation.
Content updated: View sources
QuickMedCalc is developed and maintained by an independent developer. Medical content is not independently reviewed by a physician.
Formula and medical content are based on the references listed on this page. See sources, About, and Sources and Review Process.
About
This page calculates the conventional Oxygenation Index (OI) from FiO₂, ventilator mean airway pressure, and arterial PaO₂ recorded at one matched, steady clinical time point during invasive mechanical ventilation. OI incorporates the airway pressure used to achieve oxygenation; it is not a diagnosis, a universal severity category, an ECMO criterion by itself, or an instruction to change ventilation or treatment. [1, 7, 11]
Interpretation
What the index represents
OI combines inspired oxygen, ventilator mean airway pressure, and arterial oxygen tension. A larger arithmetic value means that more inspired oxygen and/or airway pressure accompanies the observed PaO₂. It does not identify why oxygenation is impaired, measure tissue oxygen delivery, or separate lung, cardiac, shunt, perfusion, and sampling influences. [1, 7, 8]
The three values must describe one state
Use the FiO₂ and mean airway pressure displayed or measured for the invasive ventilator state paired with the arterial blood-gas PaO₂. Record ventilation mode, PEEP, position, sampling site, and time when those details matter. Do not combine data from different settings or a transient desaturation. [1, 9, 11]
PALICC-2 pediatric context
PALICC-2 uses OI or Oxygen Saturation Index (OSI) preferentially for children receiving invasive mechanical ventilation. OI ≥4 or OSI ≥5 is only one oxygenation component of the complete invasive-ventilation PARDS framework. Severity is assessed at least four hours after diagnosis: OI <16 is mild/moderate and OI ≥16 is severe. The complete framework also addresses age, onset within seven days, risk factors, imaging, and the origin of edema. Its usual severity grouping cannot be applied mechanically to special populations, including children with cyanotic congenital heart disease, chronic lung disease, or left ventricular dysfunction. This page does not collect those conditions or decide a diagnosis or severity category.[2]
Neonatal historical and protocol context
OI developed in neonatal hypoxemic respiratory-failure and extracorporeal-support literature. Preductal and postductal PaO₂ can differ. In the relevant neonatal context, a right radial artery sample is typically used for preductal oxygenation assessment, while an umbilical arterial catheter usually reflects postductal oxygenation. PPHN or a ductal-level shunt can materially change PaO₂ and OI by sampling site. Serial trends should use the same sampling site and comparable ventilator conditions when practical. This page cannot decide the right sampling site for a particular patient, and neither convention is an absolute rule for every newborn. One calculation cannot determine transfer, inhaled nitric oxide, extracorporeal support, or any other intervention. [1, 3, 4, 9]
Adult evidence is not a universal OI framework
Adult studies have evaluated OI or age-adjusted OI as research and prognostic measures. Current adult ARDS definitions instead use complete clinical frameworks built around P/F or S/F criteria, timing, imaging, edema origin, and respiratory support. Pediatric or neonatal OI thresholds must not be transferred automatically to adults. [7, 8, 10]
OI is not OSI, P/F ratio, or mean arterial pressure
OI requires arterial PaO₂. OSI substitutes pulse-oximeter SpO₂ and is a separate model. The P/F ratio omits mean airway pressure. MAP on this page means ventilator mean airway pressure—not blood-pressure mean arterial pressure, PEEP, peak inspiratory pressure, plateau pressure, or driving pressure. Do not infer ventilator mean airway pressure from any of those other values.[5, 6, 10, 11]
Technical input boundaries
FiO₂ is accepted only as 0.21–1.00 or 21–100% in the explicitly selected format. Ventilator mean airway pressure is accepted only from 1 to 100 cm H₂O and arterial PaO₂ only from 1 to 1,000 mmHg after unit normalization. These are calculator technical safety limits, not healthy, normal, diagnostic, or treatment ranges.
Trends require consistent conditions
OI is intermittent because PaO₂ requires arterial sampling. Trend interpretation requires comparable sampling and ventilator conditions. A single number does not establish prognosis and this page does not calculate mortality, recommend frequency of sampling, or generate ventilation or treatment instructions. [3, 7, 9]
References
- Ortiz RM, Cilley RE, Bartlett RH. Extracorporeal membrane oxygenation in pediatric respiratory failure. Pediatr Clin North Am. 1987;34(1):39–46. PMID 3808772. DOI 10.1016/S0031-3955(16)36179-X.
- Emeriaud G, et al. Executive Summary of the Second International Guidelines for the Diagnosis and Management of Pediatric Acute Respiratory Distress Syndrome (PALICC-2). Pediatr Crit Care Med. 2023;24(2):143–168. PMID 36661420. PMCID PMC9848214. DOI 10.1097/PCC.0000000000003147.
- Wild KT, et al. Extracorporeal Life Support Organization (ELSO): Guidelines for Neonatal Respiratory Failure. ASAIO J. 2020;66(5):463–470. DOI 10.1097/MAT.0000000000001153.
- Maratta C, et al. Extracorporeal Life Support Organization (ELSO): 2020 Pediatric Respiratory ELSO Guideline. ASAIO J. 2020;66(9):975–979. PMID 32701626. DOI 10.1097/MAT.0000000000001223.
- Muniraman H, et al. Evaluation of Oxygen Saturation Index Compared With Oxygenation Index in Neonates With Hypoxemic Respiratory Failure. JAMA Netw Open. 2019;2(3):e191179. PMID 30901051. PMCID PMC6450323. DOI 10.1001/jamanetworkopen.2019.1179.
- Rawat M, et al. Oxygen Saturation Index and Severity of Hypoxic Respiratory Failure. Neonatology. 2015;107(3):161–166. PMID 25592054. PMCID PMC4405613. DOI 10.1159/000369774.
- Dechert RE, Park PK, Bartlett RH. Evaluation of the oxygenation index in adult respiratory failure. J Trauma Acute Care Surg. 2014;76(2):469–473. PMID 24458052. DOI 10.1097/TA.0b013e3182ab0d27.
- DesPrez K, et al. Oxygenation Saturation Index Predicts Clinical Outcomes in ARDS. Chest. 2017;152(6):1151–1158. PMID 28823812. PMCID PMC5812755. DOI 10.1016/j.chest.2017.08.002.
- Gagliardi L, Barbarini M, Pugni L, Mosca F. Effect of changes in inspired oxygen tension on indexes of oxygenation in ventilated neonates. Pediatr Crit Care Med. 2002;3(1):34–38. PMID 12793920. DOI 10.1097/00130478-200201000-00009.
- Matthay MA, et al. A New Global Definition of Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2024;209(1):37–47. PMID 37487152. PMCID PMC10870872. DOI 10.1164/rccm.202303-0558WS.
- Davis MD, Walsh BK, Sittig SE, Restrepo RD. AARC clinical practice guideline: blood gas analysis and hemoximetry: 2013. Respir Care. 2013;58(10):1694–1703. PMID 23901131. DOI 10.4187/respcare.02786.
FAQ
Either is supported only with the matching explicit mode: decimal mode uses 0.60 and percentage mode uses 60; both normalize to 0.60.
Sources: [9]
The same characters can mean different oxygen fractions in the two modes. Clearing prevents silently treating 0.60 as 0.60% or 60 as a decimal fraction.
Sources: [9]
No. Mean arterial pressure is a blood-pressure measure and is not the input used in Oxygenation Index.
Sources: [1]
Yes. Select mmHg or kPa exactly as reported by the paired arterial blood gas. The calculator normalizes kPa to mmHg internally for the conventional OI equation while preserving the submitted unit in the result summary.
Sources: [11]
Yes. This formula requires arterial oxygen partial pressure from an arterial blood gas; venous or capillary PO₂ should not be substituted.
Sources: [11]
Combining mismatched settings or transient desaturation values can make the arithmetic unrepresentative of a stable oxygenation state.
Sources: [9]
OI has a long history in neonatal hypoxemic respiratory-failure and extracorporeal-support protocols. Serial values must be interpreted with gestational age, diagnosis, sampling site, reversibility, contraindications, and the complete local or specialty protocol; one value does not determine treatment.
PALICC-2 prefers OI or OSI for children receiving invasive mechanical ventilation. Its OI ≥4 definition requirement and OI 16 severity boundary apply only inside the complete PARDS framework, at the specified time, and with special-population limits; this calculator does not assign those categories.
Sources: [2]
No. OI ≥4 or OSI ≥5 is only one oxygenation component of the complete invasive-ventilation PARDS framework. The usual severity thresholds need the full framework and should not be applied mechanically to special populations, including cyanotic congenital heart disease, chronic lung disease, or left ventricular dysfunction.
Sources: [2]
Yes. Preductal and postductal PaO₂ can differ, especially with PPHN or ductal-level shunting, so the sampling site can change the calculated OI. In the relevant neonatal context, a right radial artery sample is typically preductal and an umbilical arterial catheter usually reflects postductal oxygenation; serial trends should use a consistent sampling site and ventilator conditions when practical.
Related Calculators
P/F Ratio
Calculate arterial PaO₂/FiO₂ ratio with explicit PaO₂ and FiO₂ units and FiO₂-source limitations.
A–a Gradient
Calculate estimated alveolar oxygen tension and the alveolar–arterial oxygen gradient from FiO₂, arterial PaO₂ and PaCO₂, barometric pressure, and R.
Alveolar Gas
Estimate alveolar oxygen tension with the complete alveolar gas equation and compare the common simplified clinical approximation.
Disclaimer
Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.