What is a pulse oximeter?
A pulse oximeter is a device that checks to see how much oxygen your blood is carrying.
Usually a small clip is put on the end of your finger. (Sometimes it's put on your toe or earlobe.) The device shines a light beam through the skin. It estimates your oxygen level by measuring the percentage of your blood that's carrying oxygen. Your oxygen level (or oxygen saturation, SpO2) shows on the display screen.
Pulse oximeters are used in doctors' offices and hospitals. Your doctor may think it's a good idea to use one at home. This may be the case for people who have a condition that affects their oxygen levels. Examples include people who have long-term heart or lung problems or an infection like COVID-19. Choose a device that has been approved to give accurate readings. Talk to your doctor if you want help choosing one.
Why is it used?
Usually, low blood oxygen levels cause symptoms like fatigue or shortness of breath. But with some health problems, you may not have symptoms from low blood oxygen. Your doctor may suggest checking your oxygen at different times. This can help you know when you need medical attention even if you don't have symptoms.
How do you use a pulse oximeter?
Turn on the pulse oximeter. (Check that it has batteries.) Clip it on the end of a finger. Your nail should be facing up. You'll see the results in a few seconds.
The device gives two results: your blood oxygen level (SpO2) and your pulse rate (PR). Your doctor can help you know what numbers are normal for you.
The device may not show any results if you have cold hands or you wear nail polish or artificial nails. Warm your hand, or remove the nail polish or nail. Or try a different finger.
Your doctor may suggest checking your oxygen level at different times, during exercise, or anytime your symptoms get worse. Keep a record of your levels in case you need to show it to your doctor.
When should you call for help?
Your doctor probably told you what numbers to watch for when you use your pulse oximeter. If not, here is some guidance.
Call your doctor or nurse advice line if:
- Your blood oxygen level (SpO2) drops below 95%. This is true even if the number only drops when you're active.
If you have certain health problems, like COPD, your oxygen level may always be lower than 95%. Ask your doctor what oxygen number you should expect when using your pulse oximeter. Find out which number is a sign that you should call for help.
Watch closely for changes in your health, and be sure to contact your doctor or nurse advice line if:
- Your symptoms get worse.
- You are not getting better as expected.
Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse advice line (811 in most provinces and territories) if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.
A study of 1,095 patients hospitalized with COVID-19 discovered that two easily measurable signs of health – respiration rate and blood-oxygen saturation – are distinctly predictive of higher mortality. Notably, the authors said, anyone who receives a positive COVID-19 screening test can easily monitor for these two signs at home.
This context is lacking in current guidance from the Centers for Disease Control and Prevention, which tells people with COVID-19 to seek medical attention when they experience overt symptoms such as “trouble breathing” and “persistent pain or pressure in the chest” – indications that may be absent even when respiration and blood oxygen have reached dangerous levels, the authors say.
The research was led by Drs. Nona Sotoodehnia and Neal Chatterjee, cardiologists at the UW Medicine Heart Institute in Seattle.
“These findings apply to the lived experience of the majority of patients with COVID-19: being at home, feeling anxious, wondering how to know whether their illness will progress and wondering when it makes sense to go to the hospital,” said Dr. Neal Chatterjee of the University of Washington School of Medicine.
Chatterjee and fellow cardiologist Dr. Nona Sotoodehnia were co-lead authors of the paper, which was published today in the journal Influenza and Other Respiratory Viruses.
The findings suggest that, by the time some people with COVID-19 feel bad enough to come to the hospital, a window for early medical intervention might have passed, the authors said.
“Initially, most patients with COVID don't have difficulty breathing. They can have quite low oxygen saturation and still be asymptomatic,” said Sotoodehnia. “If patients follow the current guidance, because they may not get short of breath until their blood oxygen is quite low, then we are missing a chance to intervene early with life-saving treatment.”
The researchers examined the cases of 1,095 patients age 18 and older who were admitted with COVID-19 to UW Medicine hospitals in Seattle or to Rush University Medical Center in Chicago. The study span was March 1 to June 8, 2020. The lone exclusions were people who chose “comfort measures only” at time of their admission.
While patients frequently had hypoxemia (low blood-oxygen saturation; 91% or below for this study) or tachypnea (fast, shallow breathing; 23 breaths per minute for this study), few reported feeling short of breath or coughing regardless of blood oxygen.
The study's primary measure was all-cause in-hospital mortality. Overall, 197 patients died in the hospital. Compared to those admitted with normal blood oxygen, hypoxemic patients had a mortality risk 1.8 to 4.0 times greater, depending on the patient’s blood oxygen levels. Similarly, compared to patients admitted with normal respiratory rates, those with tachypnea had a mortality risk 1.9 to 3.2 times greater. By contrast, other clinical signs at admission, including temperature, heart rate and blood pressure, were not associated with mortality.
Nearly all patients with hypoxemia and tachypnea required supplemental oxygen, which, when paired with inflammation-reducing glucocorticoids, can effectively treat acute cases of COVID-19.
“We give supplemental oxygen to patients to maintain blood oxygen saturation of 92% to 96%. It’s important to note that only patients on supplemental oxygen benefit from the life-saving effects of glucocorticoids,” Sotoodehnia said. “On average our hypoxemic patients had an oxygen saturation of 91% when they came into the hospital, so a huge number of them were already well below where we would’ve administered life-saving measures. For them, that care was delayed.”
The findings have relevance for family-medicine practitioners and virtual-care providers, who typically are first-line clinical contacts for people who have received a positive COVID-19 test result and want to monitor meaningful symptoms.
“We recommend that the CDC and [World Health Organization] consider recasting their guidelines to account for this population of asymptomatic people who actually merit hospital admission and care,” Chatterjee said. “But people don't walk around knowing WHO and CDC guidelines; we get this guidance from our physicians and news stories.”
Sotoodehnia recommended that people with positive COVID-19 test results, particularly those at higher risk of adverse outcomes due to advanced age or obesity, buy or borrow a pulse oximeter and monitor for blood-oxygen below 92%. The clip-like devices fit over a fingertip and can be purchased for under $20.
“An even simpler measure is respiratory rate – how many breaths you take in a minute. Ask a friend or family member to monitor you for a minute while you’re not paying attention to your breathing, and if you hit 23 breaths per minute, you should contact your physician,” she said.