Your red blood cells are like vehicles. Each can carry up to four oxygen molecules across your body, getting them to places like your heart and brain. Your body's vital systems need a normal percentage of oxygen inside your blood at all times, known as your oxygen saturation. However, sometimes your blood can get either too much or too little oxygen, and in these cases, there can be serious health consequences.
Oxygen levels are measured according to the percentage of oxygen saturated in your blood. This is called your SpO2 level.
Normal Blood Oxygen Levels
For medical purposes, a normal blood oxygen saturation rate is often considered between 95% and 100%. However, you may not experience any symptoms if your percentage is lower.
'Concerning' Blood Oxygen Levels
Oxygen concentrations between 91% and 95% may indicate a medical problem. People in this situation should contact their healthcare provider.
Low Blood Oxygen Levels
The medical definition of a low blood oxygen rate is any percentage below 90% oxygen saturation. Oxygen saturation below 90% is very concerning and indicates an emergency. Call 911 immediately if you or someone you know experiences such a low blood oxygen level.
When Low Oxygen Saturation Affects Your Brain
By the time your oxygen saturation has fallen to between 80% and 85%, your brain may be affected by the lack of oxygen. You may also experience vision changes.
The first visible symptoms of low blood oxygen, cyanosis causes a blue tinge to develop on your skin, particularly around your mouth and lips and beneath your fingernail matrix. This change occurs when your blood oxygen saturation reaches approximately 67%.
Low blood oxygen cases often have few or no symptoms ("silent hypoxemia"). That is sometimes even true in serious cases of hypoxemia. Some people with low blood oxygen seem well. This is why if you have reason to suspect your oxygen saturation is low, it's helpful to have a pulse oximeter. As your oxygen saturation declines, you may begin to notice some of the following symptoms:
- Shortness of breath
- Rapid breathing
- Feeling too unwell to do daily activities
Many things can cause low blood oxygen. When your body has difficulty delivering enough oxygen to your blood, any of these conditions may contribute:
Some people fear that wearing a face mask when they are sick, or to protect them against infection, may harm their body's oxygen saturation. But according to pulmonologist Jonathan Parsons, M.D., there is absolutely no danger to your oxygen levels presented by wearing even multiple face masks. Many professionals, including surgeons, must wear snug face masks for long periods of time, but nonetheless experience no harmful effects, Dr. Parsons said.
But what if you feel like you can't breathe with a mask on? That can be a consequence of mask anxiety, Dr. Parsons said. He recommends practicing slow, deep breaths if you feel it difficult to breathe while wearing a mask.
People with severe COVID-19 infections often have low oxygen in their blood. When the coronavirus infection sets into your lungs, usually about 1 week after initial symptoms, the most common symptom is shortness of breath, often with hypoxemia. These people often need supplemental oxygen, and they must be monitored by healthcare workers for signs of worsening symptoms that may progress to ARDS (acute respiratory distress syndrome).
There are primarily two ways your blood oxygen percentage is measured.
- Pulse Oximetry: A pulse oximetry reader is an inexpensive device that clips painlessly to your fingertip. It can measure the oxygen levels of your blood through the thin skin of your fingertip. Although reasonably accurate, this test can sometimes give false readings. It can be performed at home, but is also often used in hospital settings.
- ABG Test: An ABG (Arterial Blood Gas) test starts with a sample of blood drawn directly from an artery within a healthcare setting. With a blood sample, doctors and nurses can directly determine how much oxygen is in your blood. These tests are highly accurate, but must be performed by a medical professional.
Also called a "fingertip oxygen meter," the pulse oximeter is easy to use and works in seconds. Plus, it has no needle! The device clips over the tip of your index finger. People with COVID-19 are sometimes instructed by their doctors to monitor their own blood oxygen in this way. According to the New York City Department of Health, COVID-19 patients should measure their blood oxygen level twice a day: once in the morning, and once at night (unless your doctor says to use it more often). Make sure you have batteries installed, then press the clip over your fingertip. Within seconds, the screen will show you your oxygen level. There is an app available for many digital phones that can function like a fingertip oxygen meter.
However, there are some concerns and/or precautions with these items (see next slide).
The at-home finger meter is easy to use and gives fast results. But it also has limitations. Oxygen meters may have trouble reading your finger in some cases. According to the FDA, the accuracy of pulse oximeter readings can be affected by:
- Wet fingers
- Cold fingers
- Fingers with nail polish
- Use of nicotine
- Thick skin
A study of COVID-19 patients in Michigan found that patients with darker skin pigmentation stand a particular risk of false pulse oximeter readings. In that study, Black patients stood nearly three times the odds of having silent low oxygen saturation that was not detected by pulse oximeters.
Doctors may start with medication to raise your blood oxygen level. Typically, these are medicines you can inhale through an inhaler. When medication is not effective on its own, oxygen supplementation is often used against hypoxemia. There are a variety of methods, and some types of supplemental oxygen are more appropriate depending on the cause of your low oxygen. Oxygen can be given at home, while traveling, or in the hospital, depending on a person's needs. Ask your doctor what method would be best for your oxygen requirements.
The best way to protect yourself against low blood oxygen is to avoid its causes. Keep your lungs and heart in good health by exercising regularly and eating a healthy diet. Avoid infections that can cause hypoxemia such as COVID-19 by following the recommendations of health officials. Masks help protect against many of the respiratory infections that can cause low blood oxygen levels.
It is also possible for your blood to carry too much oxygen, in an oversaturation known as hyperoxia or oxygen toxicity. Hyperoxia is defined as having oxygen levels above 120 mmHg determined by an arterial blood gas test. This can lead to a wide variety of symptoms ranging from mild to life-threatening. These include:
Oxygen toxicity is typically only seen in cases involving the use of supplemental oxygen. People in these scenarios may be at risk of hyperoxia:
- Hyperbaric oxygen therapy patients
- Patients otherwise exposed to high levels of oxygen like mechanical ventilation
- Premature infants
- Underwater divers using SCUBA equipment for breathing
IMAGES PROVIDED BY:
- Hafen BB, et al. "Oxygen Saturation." In: StatPearls [Internet]. Aug. 12, 2020.
- NYC Health: "COVID-19: How to Monitor Your Oxygen Level." Nov. 9, 2020.
- Bickler, Philip E. et al. "Silent Presentations of Hypoxemia and Cardiorespiratory Compensation in COVID-19." Anesthesiology. 2021.
- Minnesota Department of Health: "Oxygen Levels, Pulse Oximeters, and COVID-19."
- Cleveland Clinic: "Hypoxemia." Mar. 7, 2018.
- Parsons, Jonathan MD. "Do masks cause lower oxygen levels?" The Ohio State University Wexner Medical Center: Aug. 4, 2020.
- NIH: "COVID-19 Treatment Guidelines: Oxygenation and Ventilation." Dec. 17, 2020.
- Gaines, Kathleen. "Know Your ABGs – Arterial Blood Gases Explained." Nurse.org. Apr. 3, 2020.
- FDA: "Pulse Oximeter Accuracy and Limitations: FDA Safety Communication."
- Sjoding, Michael W., et al. "Racial Bias in Pulse Oximetry Measurement." NEJM. Dec. 17, 2020.
- Cleveland Clinic: "Hypoxemia: Symptoms, Causes, Treatments."
- Cooper JS, et al. "Oxygen Toxicity." In: StatPearls [Internet]. Nov. 19, 2020.