What is the Oxygenation Index?

Reading Time: 2 minutes

The oxygenation index or OI is used to assess the severity of hypoxic respiratory failure. OI is now recognized as the primary indicator for respiratory disease severity stratification in mechanically ventilated pediatric patients (1). A HIGHER value represents sicker lungs.

Think of it as the P/F ratio for kids except it is also taking into account the work of the ventilator by the inclusion of mean airway pressure (MAP) (2)!

Here’s the equation:

OI = MAP x FiO2 x 100 ÷ PaO2

Don’t have an arterial line? No problem! An oxygen saturation index or OSI can be used (3,4).

OSI = MAP x FiO2 x 100 ÷ SpO2

Historically, an OI > 30 prompts the clinician to consider high-frequency ventilation. An OI > 40 has been associated with high mortality and is used as a criterion for ECMO consideration.

In pediatric acute respiratory distress syndrome, OI defines disease severity as follows…




4 ≤ OI < 8

8 ≤ OI < 16

OI ≥ 16

5 ≤ OSI < 7.5

7.5 ≤ OSI <12.3

OSI ≥ 12.3

Acute deterioration in respiratory status may not be explained by underlying cardiac disease or left ventricular dysfunction. For patients with chronic lung disease, new infiltrate on chest imaging and acute deterioration must be present (1).


  1. Pediatric Acute Lung Injury Consensus Conference Group. Pediatric acute respiratory distress syndrome: consensus recommendations from the Pediatric Acute Lung Injury Consensus Conference. Pediatr Crit Care Med. 2015;16(5):428-439. doi:10.1097/PCC.0000000000000350
  2. ARDS Definition Task Force, Ranieri VM, Rubenfeld GD, et al. Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012;307(23):2526-2533. doi:10.1001/jama.2012.5669
  3. Thomas NJ, Shaffer ML, Willson DF, Shih MC, Curley MA. Defining acute lung disease in children with the oxygenation saturation index. Pediatr Crit Care Med. 2010;11(1):12-17. doi:10.1097/PCC.0b013e3181b0653d
  4. Khemani RG, Thomas NJ, Venkatachalam V, et al. Comparison of SpO2 to PaO2 based markers of lung disease severity for children with acute lung injury. Crit Care Med. 2012;40(4):1309-1316. doi:10.1097/CCM.0b013e31823bc61b


More Posts

Related Posts

Would love your thoughts, please comment.x