Why is the pulse oximeter not reading?

Pulse Oximeters and Oxygen Saturation

Pulse oximeters are great for patients who have gone through a pulmonary rehabilitation class and are knowledgeable about oxygen, oxygen saturation, and oximeters. But what if you haven’t been through a class. What do you need to know?

A pulse oximeter works by shining a light onto the blood vessels in your fingernail and measuring the color of your blood. Blood carrying a lot of oxygen is bright red, whereas blood with lower levels of oxygen becomes more bluish/purple in color. By measuring the color, you can get an idea of how well oxygenated your blood is.

Several things can affect the accuracy of the pulse oximeter reading that you get with a finger oximeter. If you wear nail polish (especially blue, green, black or metallic ones), then the reading might be inaccurate because the oximeter cannot ‘see’ your blood through the nail polish. If you have cold hands or poor circulation, then the reading might be inaccurate too, because you are not sending enough blood to your fingertip where the reading is being taken. If you smoke, you should not waste your time and money buying an oximeter! The oximeter can’t tell the difference between blood that is carrying oxygen, and blood that is carrying carbon monoxide. Smoking increases the carbon monoxide in your blood, and the pulse oximeter can give a falsely high reading. Another thing to remember about oximetry is that there is a delay of up to 30 seconds between what goes on in your lungs and the reading that you make at the fingertip. So be patient and wait in a relaxed state as you do your reading!

The amount of oxygen in your blood is described by the “oxygen saturation” – which is literally the percentage of your blood that is ‘fully loaded’ with oxygen.

A normal blood oxygen saturation, at sea level, is about 95% or higher.

Many patients with lung disease will have an oximetry reading of 90%, but that is fine. People without lung disease also have low saturation readings when they go to a high altitude. In Denver (5,000 feet altitude), a normal saturation in a healthy person is about 90%.

You should aim to have a saturation reading above 88%.

Don’t worry if it jumps around or briefly drops below that. A reading that jumps around can be due to your activity or your circulation, a bent finger or arm, cold hands, or even due to holding your breath! But if your pulse oximeter reading consistently drops below 88%, you should report this to your physician to see if you need treatment for low oxygen levels.

Most physicians prefer that you maintain an oximetry reading of at least 90%, and for pulmonary patients, keeping it between 90 and 94% is appropriate.

The preferred level depends on your individual condition and the type of pulmonary problem that you have. This is where you should turn to your pulmonary physician for advice specific to you. Remember, each of you is an individual with different needs.

If you are observant, you will find that pacing yourself during physical activity helps to keep your oxygen saturation up.

You will probably find that your oximetry readings will be higher, or even “normal,” when you are sitting, but may drop with activity. If you are really smart, you will observe that your breathing pattern can make a big difference in your oximetry levels. You may be fascinated to see how different activities ​affect your oximetry levels. Try it​​ and see for yourself. For patients who use supplemental oxygen, physicians are often comfortable having their knowledgeable patients titrate their own oxygen needs according to their oxygen saturation, especially when traveling to different altitudes. If, however, you haven’t gone through a pulmonary rehabilitation program, or your program hasn’t taught you about oximetry, you should definitely get your physician’s advice on this before you start adjusting your own oxygen levels.

Remember that oxygen is a drug! The dose (the liter flow) should be prescribed by your doctor and changed only with your physician’s advice and permission.

Remember too that the oxygen saturation provided by an oximeter does not have the accuracy of an arterial blood gas (ABG), a test done on blood taken from an artery usually in your arm or wrist. However, oximeter readings are a lot less difficult (and less painful!) to obtain, and great for providing trends. They are certainly a lot less expensive.

We turned to PERF board member Dr. Brian Tiep for advice to those who wish to purchase their own oximeter. He is well known for his research with oxygen and breathing techniques in pulmonary patients.

My patients and I were lucky enough to work with Dr. Tiep for many years in research studies on oxygen and oximeters. There are now several on the market. Nonin is the company that invented the small finger oximeter and with which we did some of our research (see video below). Massimo and Innovo are other companies that make medical-grade pulse oximeters, but there are a lot more companies out there now that make these devices. These brands tend to be more expensive; however, we are more confident of their accuracy. Look for devices that advertise “plethysmograph and perfusion index,” as these tend to be more accurate. They are also more expensive (in the $100-$300 range) than the more everyday type of devices that can retail for as little as $15. The FDA discourages the use of the sports model for medicine and the medical model for sports. However, they are exactly the same, and you do not need a prescription for the sports models. These days, you can even get oximeters that send recordings directly to your mobile app. There is a large choice of oximeters on Amazon.com and many other stores. If you decide to purchase your own oximeter, obtain a doctor’s prescription and you may be able to deduct the cost of the oximeter from your income tax. Laws change, so check with your tax consultant. On rare occasions, an insurance company will reimburse the purchase cost if you get a prescription. It is worth checking on. However, as many oximeters are now available in stores or online and are relatively inexpensive, they can be a good low-cost investment.

We recommend an oximetry video presented by Dr. Tiep and his team.

Mary Burns, RN, BS
PERF Executive Vice President

1 Dr. Tiep discloses that he has received consultancy income from Nonin.

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