Oxygen Reserve Index (ORi™)

Current Approaches to Assessing Oxygenation

Current Approaches to Assessing Oxygenation

Masimo - ORi - Current Approaches to Assessing Oxygenation graph

Figure 1. The oxyhaemoglobin dissociation curve illustrates the relationship between SaO2/SpO2 and PaO2.

  • SpO2, arterial oxygen saturation measured by noninvasive pulse oximetry, is unable to assess in the hyperoxic range (higher than normal oxygenation) due to the flattening of the oxyhaemoglobin dissociation curve (as seen in figure 1).
  • PaO2, the partial pressure of oxygen measured by arterial blood gas, can be used as an indication of oxygenation throughout all ranges. However, results are both intermittent and delayed.
  • Between invasive samples, changes in PaO2 cannot be assessed and therefore unexpected hypoxia or unintended hyperoxia can occur.

Oxygen Reserve Index

Oxygen Reserve Index

Masimo - ORi - Oxygenation State graph

Figure 2. Range of oxygenation states that can be assessed with SaO2/SpO2, ORi, and PaO2. SaO2/SpO2 can assess hypoxia and normoxia, PaO2 can assess all ranges of oxygenation, and SpO2 with ORi provides real-time visibility from hypoxia to the moderate hyperoxic state.

  • ORi is a noninvasive and continuous parameter intended to provide insight into a patient’s oxygen status in the moderate hyperoxic range (PaO2 >100 and ≤200 mm Hg), defined as a patient’s oxygen “reserve”.
  • ORi is an index with a unit-less scale between 0.00 and 1.00.
  • ORi can be trended and has optional alarms to notify clinicians of changes in a patient’s oxygen reserve.
  • When utilised in conjunction with SpO2 monitoring (as demonstrated in figure 2), ORi may noninvasively and continuously extend the visibility of a patient’s oxygen status into ranges previously unmonitored in this fashion.
  • ORi is an index that is intended to supplement, not replace, SaO2/SpO2 and PaO2 measurements.

ORi Clinical Application

ORi Clinical Application


ORi was retrospectively obtained for this paediatric surgical case1

Masimo - ORi - Clinical Application Graph

Figure 3. ORi levels drop prior to “30% FiO2” period and “intubation” period, and minutes before the SpO2 drop. ORi then rises during re-oxygenation.

ORi with Masimo SET® pulse oximetry may provide:

  • Expanded visibility during preoxygenation prior to intubation.
  • Potential advanced warning of impending desaturation, helping clinicians intervene sooner.
  • Insight into oxygen reserve when titrating patients who are receiving supplemental oxygen.

ORi Clinical Utility

ORi Clinical Utility


In a study published in Anesthesiology, researchers found:

  • During prolonged apnea in healthy anesthetized children, ORi detected impending desaturation a median of 31.5 seconds (IQR, 19 to 34.3 seconds) before noticeable changes in SpO2 occurred.1

In a study published in Anesthesia & Analgesia, researchers found:

  • ORi may provide an advanced indication of impending desaturation in adults undergoing surgery based on trends in the relationship between ORi and PaO2.2
  • “Decreases in ORi to near 0.24 may provide advance indication of falling PaO2 when SpO2 is still >98% and above the PaO2 level at which SaO2 declines rapidly."2

Upgradable rainbow SET™ Technology Platform

Upgradable rainbow SET™ Technology Platform

Masimo - Root - ORi

Masimo rainbow SET is a noninvasive monitoring platform featuring Masimo SET® Measure-through Motion and Low Perfusion™ pulse oximetry with the option to measure multiple additional parameters.

  • Oxygen Saturation (SpO2)
  • Pulse Rate (PR)
  • Perfusion Index (Pi)
  • Pleth Variability Index (PVi®)
  • Oxygen Content (SpOC™)
  • Oxygen Reserve Index™ (ORi™)
  • Total Haemoglobin (SpHb®)
  • Methaemoglobin (SpMet®)
  • Carboxyhaemoglobin (SpCO®)
  • Acoustic Respiration Rate (RRa®)
  • Respiration Rate from the Pleth (RRp™)

Products with ORi



  1. 1.

    Szmuk P et al. Anesthesiology. 2016; 124:00-00.

  2. 2.

    Applegate et al. Anesth Analg. 2016 Mar 22.


Masimo - ORi Studies

Follow the link for available ORi studies.

Masimo - Noninvasive and Continuous ORi

Follow the link to receive more information about Noninvasive and Continuous ORi.

Masimo - Brochure, Oxygen Reserve Index


Masimo - Brochure Perioperative Care Solutions

ORi is not licensed for sale in Canada.

ORi Parameter and RRp Parameter have obtained CE Marking. Not available in the U.S.

ORi monitoring is not intended to replace laboratory blood testing. Blood samples should be analysed by laboratory instruments prior to clinical decision making.

For professional use. See instructions for use for full prescribing information, including indications, contraindications, warnings, and precautions.