What Is an Oxygenation Index?

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  • Written By: Mary McMahon
  • Edited By: Shereen Skola
  • Last Modified Date: 26 September 2019
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An oxygenation index is an assessment of how much oxygen diffuses across the membranes of the lungs and into the blood when a patient inhales. This index can be useful in the management of patients who require mechanical ventilation to breathe. Higher levels can be a sign of concern, as they may indicate an increased risk of a poor patient outcome because the patient cannot get as much oxygen out of each breath. Doctors work to lower the oxygenation index and increase the movement of oxygen from the lungs into the bloodstream.

To calculate the oxygenation index, the doctor multiplies the fraction of inspired oxygen by mean airway pressure, and divides this number by the arterial oxygen pressure. The fraction of inspired oxygen refers to how much oxygen is present in an inhaled gas mixture. Patients very rarely inhale 100% oxygen, unless they are severely ill. The mean airway pressure can be measured by checking ventilator settings to determine what the ventilator delivers to the pressure. Arterial oxygen pressure is measurable with an arterial blood gas test.


Patients on ventilators usually need constant monitoring, as they are at risk of health complications and the settings typically need recurrent adjustment. A doctor may request a regular oxygenation index check to assess the patient's performance on the ventilator. This information goes into the patient's chart along with vital signs and other observations. Reviewing the chart can provide a doctor with important information about the case, including how well the patient is responding to treatment.

Studies on the use of mechanical ventilation in patients of all ages have provided important information about the connection between oxygenation index and patient outcomes. Numerous health care facilities use a ventilator triage protocol to determine how long to keep patients on ventilators, and how to adjust the settings as patients improve or get worse. These protocols include evidence-based medicine from research, like charts showing what kinds of outcomes to expect with different oxygenation index values.

This can also be important for making long term decisions about patient care. The longer a patient stays on a ventilator, the greater the risk of pneumonia and other complications. In cases where a patient begins to deteriorate on a ventilator and appears to be fatally ill, the doctor may advise family members that the patient is unlikely to recover, and may not be able to breathe independently ever again. Family members may opt to take such patients off mechanical ventilation.


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Post 3

@allenJo - The whole point of the oxygenation index is to figure out how much oxygen you’re getting, not how hard you’re breathing.

If you want to circulate more oxygen throughout your body, I’d recommend you get on a treadmill or engage in some other aerobic exercise routine. Do that for thirty minutes in the evening before you sleep and see if it improves your sleep.

Of course, I’m not a doctor. You get no warranties with this advice, express or implied.

Post 2

@allenJo - Well, in fact you can get hooked up to such a device – but you probably can’t afford it. Hospitals offer a service where they can have you come in and sleep while they monitor you, by hooking you up to a device that will check your sleeping patterns and oxygen levels.

They hook a mask up to you as well. I knew a guy at work who did it but it cost him a lot of money. I’m not sure how much of it insurance covered.

Still, it was useful for him. They told him at several times through the evening he went a few minutes without breathing. I don’t even know how you could do that, or perhaps they defined breathing as a full intake of oxygen rather than a more passive activity.

So yes, you can get wired, but it’s a bit expensive.

Post 1

I’ve been suffering with a mild form of sleep apnea for years. It got worse several years ago when I woke up in the middle of the night with difficulty breathing. It felt like I wasn’t getting enough oxygen.

I was frightened at first because I thought it was a heart attack, and I rushed myself to the emergency room. The doctors ran a whole battery of tests on me and found out that my heart was normal.

But they had no answer at the time for the breathing difficulty. (Breathing difficulty could be anything) It was later that I found out that I had sleep apnea and the only prescription I got was to change my sleeping positions.

Sleeping on my side helped a lot, but it would sure be helpful if I could get hooked up to a device to figure out how much oxygen I’m actually getting when I sleep.

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