Oxygen saturation is the fraction of oxygen-saturated hemoglobin relative to total hemoglobin (unsaturated + saturated) in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal arterial blood oxygen saturation levels in humans are 95–100 percent. If the level is below 90 percent, it is considered low and called hypoxemia.[1] Arterial blood oxygen levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed. Continued low oxygen levels may lead to respiratory or cardiac arrest. Oxygen therapy may be used to assist in raising blood oxygen levels. Oxygenation occurs when oxygen molecules (O
2) enter the tissues of the body. For example, blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood. Oxygenation is commonly used to refer to medical oxygen saturation.
Definition[edit]
In medicine, oxygen saturation, commonly referred to as 'sats', measures the percentage of hemoglobin binding sites in the bloodstream occupied by oxygen.[2] At low partial pressures of oxygen, most hemoglobin is deoxygenated. At around 90% (the value varies according to the clinical context) oxygen saturation increases according to an oxygen-hemoglobin dissociation curve and approaches 100% at partial oxygen pressures of >11 kPa. A pulse oximeter relies on the light absorption characteristics of saturated hemoglobin to give an indication of oxygen saturation.
Physiology[edit]
Pulse oximeters are helpful because they offer a simple, noninvasive way of determining your oxygen level. But your SpO2 level can also help determine your PaO2. This is by means of the 4-5-6-7-8-9 Rule. It goes like this. 40 PaO2 equals an SpO2 of 70%; 50 PaO2 equals an SpO2 of 80%; 60 PaO2 equals an Spo2 of 90%. The brain gets affected when the SpO2 level falls below 80-85%. Cyanosis develops when the SpO2 level drops below 65%. The normal oxygen levels in a pulse oximeter usually range from 95% to 100%. Note: Normal levels may vary if you have lung disorders. In the morning, swipe up from the clock face. See your average resting SpO2 level on the SpO2 tile. It may take around an hour for your SpO2 values to appear after you wake up. The SpO2 tile shows data for your most recent sleep session. Jim – even though you might feel better at a SpO2 of 94-95%, there is no evidence that your mitochondria or cells work any better at a level above 92%. What Is Oxygen Titration? Usually, a nurse, respiratory therapist, or pulmonary function technician will measure your SpO 2 with an oximeter and then adjust the flow rate to determine how.
The body maintains a stable level of oxygen saturation for the most part by chemical processes of aerobic metabolism associated with breathing. Using the respiratory system, red blood cells, specifically the hemoglobin, gather oxygen in the lungs and distribute it to the rest of the body. The needs of the body's blood oxygen may fluctuate such as during exercise when more oxygen is required [3] or when living at higher altitudes. A blood cell is said to be 'saturated' when carrying a normal amount of oxygen.[4] Both too high and too low levels can have adverse effects on the body.[5]
Measurement[edit]
An SaO2 (arterial oxygen saturation, as determined by an arterial blood gas test[6]) value below 90% indicates hypoxemia (which can also be caused by anemia). Hypoxemia due to low SaO2 is indicated by cyanosis. Oxygen saturation can be measured in different tissues:[6]
- Venous oxygen saturation (SvO2) is the percentage of oxygenated hemoglobin returning to the right side of the heart. It can be measured to see if oxygen delivery meets the tissues' demands. SvO2 typically varies between 60% and 80%.[7] A lower value indicates that the body is in lack of oxygen, and ischemic diseases occur. This measurement is often used under treatment with a heart lung machine (extracorporeal circulation), and can give the perfusionist an idea of how much flow the patient needs to stay healthy.
- Tissue oxygen saturation (StO2) can be measured by near infrared spectroscopy. Although the measurements are still widely discussed, they give an idea of tissue oxygenation in various conditions.
- Peripheral oxygen saturation (SpO2) is an estimation of the oxygen saturation level usually measured with a pulse oximeter device. It can be calculated with pulse oximetry according to the formula[6] where HbO2 is oxygenated hemoglobin (oxyhemoglobin) and Hb is deoxygenated hemoglobin.
Pulse oximetry[edit]
Pulse oximetry is a method used to estimate the percentage of oxygen bound to hemoglobin in the blood.[8] This approximation to SaO2 is designated SpO2 (peripheral oxygen saturation). The pulse oximeter consists of a small device that clips to the body (typically a finger, an earlobe or an infant's foot) and transfers its readings to a reading meter by wire or wirelessly. The device uses light-emitting diodes of different colours in conjunction with a light-sensitive sensor to measure the absorption of red and infrared light in the extremity. The difference in absorption between oxygenated and deoxygenated hemoglobin makes the calculation possible.[6]
Medical significance[edit]
Healthy individuals at sea level usually exhibit oxygen saturation values between 96% and 99%, and should be above 94%. At 1,600 meters' altitude (about one mile high) oxygen saturation should be above 92%.[9]
An SaO2 (arterial oxygen saturation) value below 90% causes hypoxia (which can also be caused by anemia). Hypoxia due to low SaO2 is indicated by cyanosis, but oxygen saturation does not directly reflect tissue oxygenation. The affinity of hemoglobin to oxygen may impair or enhance oxygen release at the tissue level. Oxygen is more readily released to the tissues (i.e., hemoglobin has a lower affinity for oxygen) when pH is decreased, body temperature is increased, arterial partial pressure of carbon dioxide (PaCO2) is increased, and 2,3-DPG levels (a byproduct of glucose metabolism also found in stored blood products) are increased. When the hemoglobin has greater affinity for oxygen, less is available to the tissues. Conditions such as increased pH, decreased temperature, decreased PaCO2, and decreased 2,3-DPG will increase oxygen binding to the hemoglobin and limit its release to the tissue.[10]
See also[edit]
References[edit]
- ^'Hypoxemia (low blood oxygen)'. Mayo Clinic. mayoclinic.com. Retrieved 6 June 2013.
- ^Kenneth D. McClatchey (2002). Clinical Laboratory Medicine. Philadelphia: Lippincott Williams & Wilkins. p. 370. ISBN9780683307511.
- ^'Understanding Blood Oxygen Levels at Rest'. fitday.com. fitday.com. Retrieved 6 June 2013.
- ^Ellison, Bronwyn. 'NORMAL RANGE OF BLOOD OXYGEN LEVEL'. Livestrong.com. Livestrong.com. Retrieved 6 June 2013.
- ^'Hypoxia and Hypoxemia: Symptoms, Treatment, Causes'. WebMD. Retrieved 2019-03-11.
- ^ abcd'Understanding Pulse Oximetry: SpO2 Concepts'. Philips Medical Systems. Retrieved 19 August 2016.
- ^https://www.lhsc.on.ca/critical-care-trauma-centre/central-venous/mixed-venous-oxygen-saturation
- ^Peláez EA, Villegas ER (2007). 'LED power reduction trade-offs for ambulatory pulse oximetry'. Conf Proc IEEE Eng Med Biol Soc. 2007: 2296–9. doi:10.1109/IEMBS.2007.4352784. ISBN978-1-4244-0787-3. PMID18002450. S2CID34626885.
- ^'Normal oxygen level'. National Jewish Health. MedHelp. February 23, 2009. Retrieved 2014-01-28.
- ^Schutz (2001). 'Oxygen Saturation Monitoring by Pulse Oximetry'(PDF). American Association of Critical Care Nurses. Archived from the original(PDF) on January 31, 2012. Retrieved September 10, 2011.
External links[edit]
What Causes Low Spo2 Levels
Doctors will often monitor your oxygen levels. These can be monitored by using a pulse oximeter. You can monitor your own oxygen levels at home by purchasing your own pulse oximeter. Still, what is the best way of interpreting your oxygen levels? What do they mean? Here’s what to know.
What is partial pressure of arterial oxygen (PaO2)?
This is the most accurate oxygen level that we monitor. It’s how much oxygen is inside your arterial blood. A perfect reading would be 104. However, anything between 80-100 is considered acceptable. A PaO2 of 60-79 is considered mild hypoxemia. A PaO2 of 40-79 is considered moderate hypoxemia, and a PaO2 of less than 40 is considered severe hypoxemia.
Hypoxemia is a fancy term for a low arterial blood oxygen level. Most experts accept the PaO2 value of 60 as the baseline value we want to maintain. If COPD is causing a PaO2 of less than 60, supplemental oxygen is indicated. Usually, with COPD, all that is needed is a low flow of 2-3 LPM. This is usually all that is needed to maintain a PaO2 of 60 or better. If you want, you can read my article, 'How To Qualify For Home Oxygen Therapy?'
There is only one way to learn what your PaO2 is. It is to draw blood from one of your arteries. The artery we usually draw it from is the radial artery. This is an artery that is near the surface on the thumb side of the back of your wrist. This test is called an Arterial Blood Gas (ABG). This is an invasive blood draw.
What is oxygen saturation (SpO2)?
SpO2 is another oxygen level. It’s the percentage of oxygen molecules you inhale that make it to your arterial blood. A perfectly normal value is 98%. However, anything greater than 90% is considered acceptable. For some people with COPD, doctors consider anything between 88-92% to be acceptable.
This value is determined using a pulse oximeter. It’s a small, hand-held device that you slip over a finger, toe, or earlobe. You can purchase these in stores. The ones you buy for your home are usually ones that slip over your finger.
These devices can be purchased for less than $30. You can get them from online stores like Amazon. I have seen them at stores like Aldi. The trick here is that you will want to make sure the one you buy is FDA approved. This will ensure that you are getting an accurate reading.
How are pulse oximeters helpful?
What's A Good Spo2 Level
Pulse oximeters are helpful because they offer a simple, noninvasive way of determining your oxygen level. But your SpO2 level can also help determine your PaO2. This is by means of the 4-5-6-7-8-9 Rule.
Good Spo2 Level
It goes like this.
- 40 PaO2 equals an SpO2 of 70%
- 50 PaO2 equals an SpO2 of 80%
- 60 PaO2 equals an Spo2 of 90%
Basically, you take your SpO2 value minus 30. This gives an 'estimate' of where your PaO2 stands. By doing my own experiments, I have determined this 'estimated' PaO2 to be pretty accurate.
Normal Spo2 Levels While Sleeping
So, if your pulse oximeter gives you a reading of 90%, this means that your estimated PaO2 is 60. That’s right about where we want it. This is why the hospital I work for has a policy of maintaining a SpO2 of 90%. There are some exceptions that we can discuss in a future post if you want.
A helpful tool
Pulse oximeters are nice. They allow you and doctors to monitor your oxygen level at pretty much any time and place. It’s simple, painless, and accurate as long as you have a pulse oximeter that is FDA approved. You should talk to your doctor about determining what SpO2 level is best for you. For most people, it’s 90% or better. However, with some people with COPD, 88% is acceptable too. To learn what oxygen levels are best for you, talk to your COPD doctor.
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