Normal O2
By Mandy Concepcion
- What is the Normal Oxygen Level So what is the normal oxygen level? People who are breathing normal, who have relatively healthy lungs (or asthma that is under control), will have a blood oxygen level of 95% to 100%. Anything between 92% and 88%, is still considered safe and average for someone with moderate to severe COPD.
- Nasal cannula, we assume that the fraction of oxygen that is inspired (above the normal atmospheric level or 20%) increases by 4% for every additional liter of oxygen flow administered. For a Nasal Cannula: Oxygen tank. In liters / min. FiO2- Fraction of Inspired Oxygen value 0 (no oxygen, just room air).20 1 L / min.24 2 L.
Normal O2 Stats
Blood oxygen levels fall below normalbounce right back when you provide them with the oxygen they are used to getting. When you increase your oxygen flow rate due to activity you are restoring “normalcy” to the system. Please remember the landmark work of Dr. Petty and his colleagues regarding oxygen therapy, activity, and survival.
The O2 sensor measures the oxygen content of the exhaust. The O2 sensor’s sensing ability comes about by producing a small voltage proportionate to the exhaust oxygen content. In other words, if the oxygen content is low it produces a high voltage (0.90 Volts - Rich mixture) and if the oxygen content is high it produces a low voltage (0.10 Volts - Lean mixture). Although theoretically the O2 sensor should cycle between 0.00 volts and 1.00 volts, in reality it cycles between 0.10 volts and 0.90 volts.
A GM O2 sensor signal stuck at 450 mV is an indication of an open O2 sensor circuit (signal wire) or faulty O2 signal ground. The 450 mV value (GM) is called a bias voltage and it is not the same for all manufacturers. Some manufacturers employ a dedicated O2 sensor ground. Such a ground lead is attached to the engine block or chassis and feeds an ECM O2 ground pin only. The O2 circuit is then grounded through the inside of the ECM electronic board by this ground wire. A loss of this ground would also put the O2 sensor signal at around 450 mV, which also makes it look like an open circuit. The same holds true for Chrysler, but these use a different O2 bias voltage, which is usually 2.00 to 4.00 volts.
1) A few key issues are very important in the analysis of O2 sensor signals.
2) An O2 sensor will cycle between 0.10 to 0.90 or almost 1 volt.
3) An O2 sensor has to reach the 0.8x Volts amplitude mark while at full operation.
4) An O2 sensor also has to reach the 0.1x Volts amplitude mark while at full operation.
5) Full operation means the engine is fully warmed up, O2 sensor above the 600 deg. F. operating temperature, and no fuel or mechanical problems present.
6) The O2 sensor must cycle at least once per second, which would show 3 cross counts on the scan tool PID.
7) Silicone is the leading cause of O2 contamination.
8) It is easier for an O2 sensor to go from rich to lean than vise-versa.
9) O2 sensors tend to fail on rich bias. In other words, they tend to shift their cycling to the upper side or rich side of the voltage scale.
10) Contrary to what many people think, an O2 sensor WILL NOT cycle by itself. The O2 sensor cycle is a direct result of the ECM response to the changes in the mixture.
11) Any time the O2 cycles and crosses the 0.450 volts mark, the system is in CLOSE-LOOP.
12) Even though an O2 sensor is cycling and crossing 0.450 volts (ECM in close loop) it DOES NOT mean that it is working properly.
13) O2 sensor operation is extremely important not only to keep HC & CO emissions low but also to the NOx as well.
14) Proper O2 sensor cycling will determine the catalytic converter’s efficiency. The catalytic converter needs the O2 sensor cycling at its proper amplitude and frequency for it to function at its maximum efficiency.
15) An O2 sensor with a high voltage reading does not necessarily mean that the mixture is rich or high in fuel content. An EGR valve problem will send the O2 signal high as well.
A big misconception among technicians trying to understand O2 sensors is that they cycle by themselves. The O2 sensor just reads oxygen content in the exhaust, THAT’S IT. Excess oxygen in the form of regular ambient air will send the O2 sensor voltage signal low (under 0.450 volts) and lack of it will send the voltage signal high (over 0.450 volts). A stuck open EGR valve will create a lack of oxygen in the exhaust, since the re-circulating exhaust has all its oxygen already burnt . The ECM sometimes uses the O2 sensor to check for proper EGR operation and sets a code if necessary. So, be aware of the fact that a vehicle might be running lean because the ECM sees a rich O2 signal due to a defective (stuck open) EGR valve. Since the ECM sees a rich signal, it will try to correct with a lean command and try to lower the O2 sensor’s high voltage signal.
CONDITION THAT AFFECT OPERATION
NOTE: WHEN PERFORMING O2 SENSOR CHECKS, IT IS IMPORTANT TO TAKE MEASUREMENTS AT IDLE AND 2000 RPM. BE AWARE THAT O2 SENSOR PRE-CONDITIONING IS IMPORTANT, EVEN ON THE NEWER STYLED HEATED O2 SENSORS. PRE-CONDITION THE O2 SENSOR BY RAISING THE ENGINE SPEED TO 2000 RPM FOR ABOUT 15 SECONDS OR SO. THE O2 SENSOR HAS TO BE ABOVE 600 º F. TO BE ABLE TO OPERATE PROPERLY. LONG PERIODS OF IDLE TIME CAN RENDER A NON-HEATED OR OLDER O2 SENSOR TOO COLD FOR IT TO FUNCTION AT ALL. AT THE SAME TIME, DO NOT TRY TO FORCE A HEATED O2 SENSOR INTO OPERATION. AN O2 SENSOR WITH A FAULTY HEATER WILL GO INTO CLOSED-LOOP AFTER A GOOD WARM-UP SESSION.
Why did my doctor prescribe oxygen for me?
Every body needs oxygen. In fact, every tissue and every cell in the body needs a constant supply of oxygen to work properly.
Oxygen gets into our cells and tissues via the lungs. The lungs breathe in oxygen from the air, then pass the oxygen into the bloodstream through millions of tiny air sacs called alveoli. Hemoglobin in the red blood cells then picks up the oxygen and carries it off to the body's tissues and cells.
Interstitial lung disease can cause inflammation and/or scarring (aka fibrosis) in the part of the lung tissue where oxygen passes into the bloodstream — the alveoli. This inflammation and/or scarring make it difficult for oxygen to move into the bloodstream. Therefore, the amount of oxygen in the blood drops, and the body's tissues and cells may not receive enough oxygen to keep functioning properly. Not enough oxygen in the bloodstream is called hypoxemia.
How did my doctor determine that I need supplemental oxygen?
The amount of oxygen in the bloodstream can be easily measured two ways:
- Oximetry This is the method used most often. A small, clip-on device shines a light through your finger or earlobe and measures the amount of light absorbed by the oxygen-carrying hemoglobin in the red blood cells. By calculating the amount of light absorption, the device can measure how saturated the hemoglobin is with oxygen molecules, or O2 sat. Normally, the oxygen saturation of the blood is around 98 to 100 percent.
- Arterial blood gas study In this procedure, blood is drawn out of an artery, usually in the wrist, using a needle and syringe. The blood is then sent through an analyzer to measure the amount of oxygen gas dissolved in the blood. This result is called the arterial oxygen pressure (paO2), and is normally 80 to 100 mm Hg.
The body needs enough oxygen to keep the blood adequately saturated, so that cells and tissues get enough oxygen to function properly. Furthermore, cells and tissues can neither 'save up' nor 'catch up' on oxygen — they need a constant supply. When the oxygen saturation falls below 89 percent, or the arterial oxygen pressure falls below 60 mmHg — whether during rest, activity, sleep or at altitude — then supplemental oxygen is needed.
Your health care provider can determine your supplemental oxygen needs by testing you while you are at rest and while walking, and can also order an overnight oximetry study to test your oxygen saturation at night. A high altitude simulation test is also available to test your oxygen saturation at 8000 ft (the cabin pressure of most airliners).
When and how often do I have to wear my oxygen?
Your health care provider will write a prescription for when and how much you should wear your oxygen, based on the results of your testing. The prescription should specify the following:
- The appropriate oxygen flow rate or setting, expressed as liter flow of oxygen per minute (lpm or l/min) that will keep your saturations at or above 90 percent
- When you should wear your oxygen (for instance, during activity, overnight or continuously)
- The type of equipment that will accommodate your lifestyle needs
Why would I need to wear oxygen while sleeping?
Everyone's oxygen levels in the blood are lower during sleep, due to a mildly reduced level of breathing. Also, some alveoli drop out of use during sleep.
If your waking oxygen saturation is greater than about 94 percent on room air, it is unlikely that your saturation during sleep will fall below 88 percent. However, your doctor can order an overnight oximetry test if there is a question about your oxygen saturation levels while you are sleeping.
How do I know that I'm using the right amount of supplemental oxygen?
To determine if you're getting the right amount of supplemental oxygen, your oxygen saturation must be measured while you are using your oxygen. Your provider or a respiratory therapist from the oxygen supplier should test your oxygen saturation on oxygen while you are at rest, while walking and, if indicated, while you are asleep. As long as your saturation is in the 90s, you are getting the right amount of supplemental oxygen.
Should I buy my own finger oximeter to test my oxygen saturations?
It is probably a good idea to buy a finger oximeter, so that you are sure you are getting the right amount of supplemental oxygen. Finger oximeters are available on the internet, through medical supply companies and even in sporting goods stores.
How will using supplemental oxygen benefit me?
When a person isn't getting enough oxygen, all organs of the body can be affected, especially the brain, heart and kidneys. Wearing supplemental oxygen keeps these organs, and many others, healthy. There is evidence that, for people who are hypoxemic, supplemental oxygen improves quality of life, exercise tolerance and even survival.
Supplemental oxygen can also help relieve your symptoms. You may feel relief from shortness of breath, fatigue, dizziness and depression. You may be more alert, sleep better and be in a better mood. You may be able to do more activities such as traveling, including traveling to high altitudes.
Symptoms such as shortness of breath may be caused by something other than lack of oxygen. In these cases, supplemental oxygen may not relieve the symptom. But if tests show you are not getting enough oxygen, it is still important to wear your oxygen.
Normal O2 Sat%
Does my need for supplemental oxygen mean that I don't have long to live?
People live for years using supplemental oxygen.
Will I always need to use supplemental oxygen?
Normal O2 Levels In Blood
That depends on the reason oxygen was prescribed. If your lung or heart condition improves, and your blood oxygen levels return to normal ranges without supplemental oxygen, then you don't need it anymore.
Can I become 'dependent on' or 'addicted to' oxygen?
There is no such thing as becoming 'dependent on' or 'addicted to' supplemental oxygen — everybody needs a constant supply of oxygen to live. If there is not enough oxygen in your bloodstream to supply your tissues and cells, then you need supplemental oxygen to keep your organs and tissues healthy.
Does supplemental oxygen cause side effects?
It is important to wear your oxygen as your provider ordered it. If you start to experience headaches, confusion or increased sleepiness after you start using supplemental oxygen, you might be getting too much.
Oxygen settings of 4 liters per minute or above can cause dryness and bleeding of the lining of the nose. A humidifier attached to your oxygen equipment or certain ointments can help prevent or treat the dryness. For more information, see 'Higher Oxygen Flows' in Your Oxygen Equipment.
Will I be able to go out and about with my oxygen equipment?
Normal O2 Saturation
The goal is to have you continue as many of your usual activities as you can. You should work with your health care provider and oxygen supply company to get oxygen equipment that will allow you to do these things. Choosing the right type of equipment for you and your lifestyle is very important — the right ambulatory oxygen equipment can play a major role in improving quality of life.
Next:
Supplemental Oxygen Index:
UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your provider.
Related clinics
Lung Transplant Program
400 Parnassus Ave., Fifth Floor
San Francisco, CA 94143
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