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Nocturnal Hypoxemia: Reasons for Low Oxygen Levels While Sleeping

There’s nothing better than getting a good night’s sleep and waking up feeling refreshed. However, many people have sleep problems that prevent them from getting the rest they need. Nocturnal hypoxemia is a condition where oxygen levels in the blood drop too low during sleep, and it's a result of an underlying medical issue. Learning more about this condition and how to manage it can help improve sleep and overall health.

What is nocturnal hypoxemia?

Hypoxemia is when blood oxygen levels are lower than usual. When this happens during the night while the person is asleep, it's called nocturnal hypoxemia.

Healthy blood oxygen levels typically range between 95–100%. Normally, people are expected to have a small oxygen level drop when they are sleeping. However, for people with certain medical conditions, these levels can drop too low — when a person is asleep, and their blood oxygen levels are less or equal to 90%, it's defined as nocturnal hypoxemia.

How it affects your sleep

Waking up feeling refreshed and having enough energy for daily tasks are signs of healthy sleep. But if you have a condition that leads to nocturnal hypoxemia, your sleep might not be so great. Here's why:

  • It can cause sleep fragmentation. The body’s natural response to low oxygen levels is to prompt partial awakenings to increase respiratory efforts and help the individual take in more oxygen.
  • It makes you feel overly tired. Some people with hypoxemia during sleep experience daytime symptoms such as excessive daytime sleepiness, fatigue, and irritability.

Reasons for low oxygen levels while sleeping

Hypoxemia doesn't happen on its own; it's a result of another medical issue. Generally speaking, any condition that affects efficient gas exchange in the lungs or blood flow through the body could result in hypoxemia. Causes of nocturnal hypoxemia include:

Obstructive sleep apnea (OSA)

Obstructive sleep apnea (OSA) is a common condition in which the muscles in the back of the throat relax too much during sleep. This blocks or narrows the airway, making it hard for air to reach the lungs. People with OSA stop breathing repeatedly during the night. As a result, the amount of oxygen in the blood goes recurrently down.

Chronic obstructive pulmonary disease (COPD)

COPD is a group of diseases that affect the lungs and make it difficult to breathe. Individuals with COPD often deal with sleep-related breathing disorders such as OSA, leading to nocturnal hypoxemia, which is present in up to 70% of those with COPD. In general, the more severe COPD is, the more the chance of having nocturnal hypoxemia.

Scientists are still trying to understand why people with COPD experience drops in blood oxygen levels during sleep.

Sickle cell disease

Sickle cell disease is a group of conditions that change the shape and characteristics of red blood cells. Abnormal red blood cells clump and cause blockages in the blood flow, blocking oxygen delivery to tissues. With this disease, the blood cells die earlier than normal, which causes a shortage of them, leading to anemia.

In the case of sickle cell disease, there aren’t enough healthy red blood cells to carry oxygen through the body, so less oxygen reaches the organs and tissues.

It’s common for individuals with sickle cell disease to experience sleep-related breathing problems such as OSA that lead to nocturnal hypoxemia. As we have seen, OSA can contribute to nocturnal hypoxemia by reducing the amount of oxygen that gets into the bloodstream.

However, nocturnal hypoxemia was found in both adults and children with sickle cell disease without OSA.

Heart conditions

Some people with severe heart problems experience low blood oxygen levels at night. In a study with 183 patients with heart failure, almost 83% had nocturnal hypoxemia.

In those with heart failure, the heart can’t pump blood effectively. This can lead to fluid buildup in the lungs, which can interfere with the normal exchange of oxygen and carbon dioxide. As a result, oxygen levels in the blood can decrease, especially when lying down during sleep, due to the redistribution of fluid.

Additionally, many people with heart conditions may also have sleep-related breathing disorders like OSA, which can lead to nocturnal hypoxemia.

Neuromuscular disorders

Some neuromuscular disorders cause the muscles responsible for breathing to weaken. As a result, the lungs can’t fully expand and contract, leading to shallow breathing and poor oxygenation of the blood, particularly during sleep.

High altitude

Our bodies struggle in high altitudes, like places at least 2,400 meters or 8,000 feet above sea level. At high altitudes, the air pressure is low, meaning there’s less oxygen available for breathing, therefore, shortness of breath is a normal effect of high altitude.

Breathing is slower during sleep, and it can be harder to maintain adequate oxygen levels. Fortunately, spending a few days in the area usually lessens the negative effects on breathing.

Sleep position

Some evidence suggests that blood oxygen levels in highlanders might be better when sitting or standing up than when lying on their back when asleep. However, there is no evidence that sleeping on your back would influence blood oxygen levels in people living in lowland areas.

Lying on your back can worsen OSA, which can lead to drops in blood oxygen levels. If you have OSA, consider trying different sleeping positions, such as lying on your side.

Nocturnal hypoxemia symptoms

It wasn't possible to establish a direct link between nocturnal hypoxemia and specific symptoms in the literature. However, we know that low oxygen levels can cause a variety of symptoms, such as difficulty focusing, excessive fatigue, anxiety, shortness of breath, rapid breathing, and heart rate changes, which are easier to notice when the person is awake.

If you notice that your skin or lips have turned blue, you start feeling confused, and you experience rapid heart rate and breathing — seek medical attention right away.

How it is diagnosed

Nocturnal hypoxemia isn't considered a medical condition but rather a sign of an underlying health issue. Doctors have different ways to check if someone has low oxygen levels in their blood while they sleep, including:

  • Continuous pulse oximetry. It involves wearing a small device called a pulse oximeter on your finger or earlobe while you sleep. This device measures the oxygen saturation levels in your blood.
  • Arterial blood gas (ABG). A test that measures oxygen and carbon dioxide in blood taken from an artery.
  • Polysomnography (PSG) is a test that doctors use to diagnose sleep disorders, such as OSA, that could lead to nocturnal hypoxia. PSG records various body functions during sleep, like your brain waves, heart and breathing rates, and eye and leg movements. It can also include pulse oximetry to track oxygen levels in your blood.

Treatment for nocturnal hypoxemia

Nocturnal hypoxemia can happen due to various reasons, and fixing it involves dealing with those underlying causes. Management will depend on the cause and severity of the condition and may involve a range of treatments and medications.

Supplemental oxygen

Supplemental oxygen therapy provides extra oxygen to people with breathing disorders, such as COPD, asthma, and pneumonia. It’s delivered via oxygen tanks or concentrators and helps improve oxygen levels in the blood.

Continuous positive airway pressure (CPAP)

CPAP machines are used to treat sleep-related breathing problems like OSA. They work by delivering a constant flow of air through a mask that you wear while you sleep. This air pressure helps keep the airways open, preventing pausings in breathing and, thus, reductions in oxygen levels.

Ventilatory assistance devices

Non-invasive ventilation (NIV) can help people with neuromuscular disorders breathe better. Instead of using invasive procedures like endotracheal intubation, a machine delivers air through a face or nasal mask. NIV can improve breathing efficiency and, consequently, help optimize blood oxygenation.

Medications

Depending on the causes of nocturnal hypoxemia, your doctor may prescribe medications to treat it. For instance, drugs called beta-agonists can be used to treat lung disease. They work by relaxing the muscles around the airways, making it easier to breathe.

Inhaled anticholinergic medications, like ipratropium bromide and tiotropium, widen the airways, helping to manage COPD.

Corticosteroids like methylprednisolone may also be prescribed to people with certain respiratory diseases.

Prevention strategies

Preventing nocturnal hypoxemia usually involves managing the health condition that’s causing it and minimizing risk factors for developing diseases associated with lower oxygen levels during sleep, such as OSA. Possible ways to do that may include maintaining a healthy lifestyle and avoiding smoking, alcohol, and sedative substances.

Complications of nocturnal hypoxemia

When blood oxygen levels drop too low, organs and tissues don’t receive enough oxygen to function properly. We call this hypoxia, and if it persists for a long time, it can cause serious damage. Some possible complications of nocturnal hypoxemia are:

  • Cardiovascular effects. Low oxygen at night has been linked to high blood pressure in people with OSA.
  • Cognitive impairment. Low blood oxygen levels during sleep can make you feel excessively tired during the day, making it hard to focus, solve problems, and remember things.
  • Reduced quality of life. Breathing issues during sleep, such as OSA, can lower blood oxygen levels. This can mess with your sleep quality, leading to difficulties in the daytime and lower quality of life.

Recent research

Researchers are using wearable technology to track real-time physiological data, including heart rate, breathing, and oxygen levels. This method could potentially help detect health problems like sleep apnea, irregular heart rhythms, and nocturnal hypoxemia.

Another group of scientists is using artificial intelligence models that could help predict heart diseases and facilitate early interventions while taking into consideration factors like OSA and nocturnal hypoxemia.

If your blood oxygen levels drop too low during sleep, it means that something’s likely not right with your health. Nocturnal hypoxemia can indicate several health conditions. Some of them can have serious consequences for your physical and mental well-being, so it's best not to ignore them. If you’re experiencing symptoms of nocturnal hypoxemia, such as sleep interruptions or daytime fatigue, it’s essential to seek medical help.

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