What You Need to Know About the Oxygen Desaturation Index (ODI) and Sleep

The oxygen desaturation index (ODI) is a measure of insufficient blood oxygen during sleep. If you have a diagnostic sleep study, this can be one of the components in the report that you receive describing your results.

Oxygen saturation is a measure of the oxygen in your blood. Oxygen desaturation (low oxygen saturation) means that the percentage of oxygen in your blood is lower than it should be.

Low oxygen saturation is one of the indicators that you could be at risk of long-term health consequences, such as cardiac (heart) disease and dementia.

Learn how oxygen desaturation is measured and how the results may be helpful for identifying sleep apnea and other conditions that may be associated with drops in oxygen level during sleep.

What Is the ODI?

The ODI is the number of times per hour of sleep that your blood oxygen level drops by a certain degree from baseline. Drops in blood oxygen level are called desaturations.

Desaturations can occur due to illnesses (like lung disease) while you are awake, but they are even more likely to occur while you are asleep. Sleep apnea is the most common cause of oxygen desaturation during sleep.

The ODI is typically measured as part of standard sleep studies, such as:

• Polysomnogram
• Home sleep apnea testing
• Overnight oximetry

Blood arterial oxygen saturation and desaturation is a measure of the oxygen percentage in the arteries, which are the blood vessels that contain the highest percentage of oxygenated blood in the body. Arterial oxygen saturation can be measured during waking and sleep with non-invasive testing.

Several other aspects of your breathing can affect your oxygen saturation and your ODI results, and they are each separately reported as part of a comprehensive sleep study:

• Respiratory rate—how fast you breathe
• Apnea—episodes of paused breathing lasting for at least 10 seconds
• Hypopnea—inadequate or shallow breathing episodes lasting for at least 10 seconds with at least 4% oxygen desaturation and at least 30% reduction in airflow
• The absolute minimum blood oxygen level measured, which may be called the minimum oxygen saturation or the oxygen nadir of the study

Scoring Guidelines

Normal oxygen saturation should be 96 to 97%. A drop below 90% is considered mildly abnormal, between 80 to 89% is considered moderately abnormal, and below 80% is considered severely abnormal.

Your ODI is scored based on how much and how often your oxygen level drops during the test. The degree of change from baseline can be measured in two different ways.

The criteria used to determine the index may vary depending on the scoring rules used:

• According to guidelines from the American Academy of Sleep Medicine, any respiratory event during sleep with a 3% drop in blood oxygen levels is counted towards the total. For example, a change from 95% to 92% would be an event that is counted toward the index's total.
• However, Medicare and some other insurances still rely on older scoring rules and require a 4% change for an event to be counted toward the index.

An ODI score that indicates frequent or severe desaturations correlates with substantially reduced oxygen levels, but it does not identify the cause of the problem. Your healthcare provider would determine the cause of your desaturation by considering your medical history, physical examination, and possibly other diagnostic tests as well.

Generally, longer and deeper desaturations are associated with worse obstructive sleep apnea (OSA), and scoring criteria are designed to reflect these components.

What Causes Worsened ODI?

During sleep, muscle tone diminishes a little. This doesn't have a noticeable or substantial effect for most people.

But the normal decline in muscle tone during sleep means that ODI can be worsened by illnesses that affect breathing or blood oxygen.

Apnea and Hypopnea

When breathing becomes disrupted during sleep, the oxygen levels of the blood can fall repeatedly. With OSA and other conditions that affect ODI, these drops are typically associated with apnea or hypopnea.

• Obstructive apnea is a complete interruption of breathing. It is the most common symptom of OSA, and it occurs due to blockage of the upper airway, usually due to the increased tendency of the throat muscles to relax during sleep.
• Central sleep apnea is far less common than OSA. It is a pause in breathing during sleep that is caused by impaired control of breathing from the brain or from heart failure or poor heart function.
• Hypopnea is an episode of impaired breathing that represents a partial collapse of the airway.
• Oxygen drops can occur due to snoring or upper airway resistance syndrome (UARS), two conditions in which breathing is disturbed, yet to a lesser degree than OSA.

The ODI differs from the apnea-hypopnea index (AHI), which is another measurement. The AHI also includes events that may cause arousals or awakenings from sleep without affecting oxygen levels.

Sleep fragmentation, which is an interruption of sleep, can occur due to these breathing issues. Sleep interruptions can happen with or without the associated desaturations. Even when sleep fragmentation occurs without an effect on oxygen saturation, it can cause sleepiness during the day due to an inadequate amount of restorative sleep.

Other Causes

Other conditions can cause problems with breathing and/or oxygenation during sleep and affect your ODI.

For example:

• Obesity hypoventilation syndrome makes it hard to breathe adequately and can affect your oxygen levels during waking or sleep, but especially during sleep.
• Neuromuscular diseases can impair your ability to move your muscles for breathing and can cause or contribute to ODI.
• Heart diseases, like congestive heart failure or mitral valve disease, or lung diseases, including chronic obstructive pulmonary disease (COPD) often coexist with OSA but can cause ODI even without co-existing OSA.

Several of these conditions contribute to each other, and OSA often coexists with other medical issues that affect breathing, such as COPD.

Additionally, if you have OSA and another underlying health problem that affects your oxygen level, the effects on your oxygen level during sleep can be substantially worse. With decreased lung capacity reserves or diminished heart function, the collapse of the upper airway may cause your blood's oxygen levels to drop more quickly and to a larger degree than they would if you had only OSA.

Health Consequences

Recurrent episodes of oxygen desaturation can lead to hypoxemia (diminished blood oxygen) and hypoxia (diminished oxygen in the body tissues).

Hypoxia and hypoxemia can be harmful to your body, especially if the problem is prolonged and recurrent.

Furthermore, ODI may also be associated with:

• An increased level of carbon dioxide, which can be harmful to your health
• Oxidative stress and free radical formation in the body
• Associated bursts of cortisol due to oxygen deficiency
• Insulin resistance and increased risk of diabetes
• Daytime sleepiness and difficulty with concentration
• Altered metabolism and obesity

These factors may predispose to long-term cardiovascular risks, including hypertension (high blood pressure), cancer, heart attack, stroke, arrhythmias like atrial fibrillation, and memory loss associated with dementia. These consequences are an active area of sleep research.

Treatment

The treatment for ODI abnormalities during sleep depends on the cause. Generally, OSA, the most common cause of ODI problems, is treated with continuous positive airway pressure (CPAP), which can normalize breathing and reduce the long-term risks associated with untreated sleep apnea.

Sometimes other sleep apnea treatments, including surgery, are considered as a treatment for OSA that doesn't improve with more conservative measures.

Treatment for other causes of ODI problems can involve management of the underlying contributing factors and may include weight loss. Sometimes treatment of lung disease or heart disease can help improve ODI.

And for some people who have OSA or other causes of ODI problems, home oxygen supplementation can be helpful.

Frequently Asked Questions (FAQs)

What is a normal oxygen desaturation index level?

Although a normal oxygen desaturation index level has not been universally established, the most common level to be considered normal is fewer than five desaturation episodes per hour of sleep.

Which finger is best to use for a pulse oximeter to measure an ODI level?

A pulse oximeter clip can be used with any finger, but one study suggests that for those who are right-hand dominant, the right middle finger and right thumb provide the most accurate measure of ODI level. Also, in the study, for the limited number of participants who were left-hand dominant, the left middle finger and left thumb gave the most accurate ODI reading.

What is a dangerously low oxygen level?

Any blood oxygen level below 95% warrants medical concern, and immediate medical attention is needed for an oxygen level below 85%.

A Word From Verywell

If you are feeling tired during the day or having difficulty concentrating despite a normal amount of sleep, you could be experiencing sleep disruption and/or abnormal ODI. Talk to your healthcare provider about whether a sleep study would be useful for figuring out what is going on and determining the best treatments for your condition. Resolving sleep-disordered breathing may benefit both sleep quality and long-term health.