Oxygenation Index (OI)

OI = (MAP × FiO₂ × 100) ÷ PaO₂, where MAP is mean airway pressure in cmH₂O, FiO₂ is the inspired-oxygen FRACTION (0.21–1.0), and PaO₂ is arterial oxygen tension in mmHg; the result is a unitless index displayed to one decimal. The FiO₂ unit is load-bearing, not a detail: PALICC-2 (2023) prints this index as MAP(cmH₂O) × FiO₂(percent) ÷ PaO₂(mmHg), and the explicit ×100 above is precisely what converts a fraction into that percentage form, so the two renderings are the same number (the ×100 form is written out in Slaughter 2025). Applying both conventions, or neither, is a 100-fold error in opposite directions; a worked example in the test suite pins the magnitude so the factor cannot be simplified away. Bands are matched against the raw unrounded value using the PALICC-2 (2023) two-tier scheme: OI < 4 is below the invasive-ventilation oxygenation criterion, 4 ≤ OI < 16 is mild–moderate, and OI ≥ 16 is severe.

OI is the mean airway pressure times FiO₂ times 100, divided by the arterial oxygen tension (PaO₂) — higher OI means a worse oxygenation defect. It requires an arterial line (for the PaO₂) and is defined only on positive-pressure ventilation, where a mean airway pressure exists (conventional IMV or HFOV); it is undefined for spontaneous breathing, nasal cannula, or standard non-invasive masks. FiO₂ is entered as a fraction here and the ×100 converts it to the percentage form the guideline prints: PALICC-2 (2023) states OI as MAP(cmH₂O) × FiO₂(percent) ÷ PaO₂(mmHg), which is the identical number. This is the single most likely implementation error in the score — apply both conventions and the index is 100× too large, apply neither and it is 100× too small — so if a value here disagrees with another calculator by a factor of 100, that is the first thing to check. Interpretation bands here are the PALICC-2 (2023) two-tier scheme for invasively ventilated children: the oxygenation criterion is OI ≥ 4 and severe is OI ≥ 16. PALICC 2015 used a three-tier scheme — mild (4 ≤ OI < 8), moderate (8 ≤ OI < 16), severe (OI ≥ 16) — and PALICC-2 collapsed the two lower tiers into mild–moderate while leaving the OI severe cutoff (≥ 16) unchanged, so unlike OSI (whose severe cutoff moved from 12.3 to 12) no OI number changed between editions; this implementation applies the PALICC-2 (2023) edition. The map_awp (5–50 cmH₂O) and pao2 (10–700 mmHg) numeric limits are engineering input-validation bounds, not values from a specific publication [NEEDS SOURCE]. OI classifies a physiologic defect; it is not an individual-patient outcome prediction.