A pulse oximeter is a painless and reliable way for clinicians to measure a person's blood oxygen levels.
When you breathe, oxygen enters your lungs, passes through thin membranes and enters your blood stream — where it's then picked up by red blood cells and carried around the body to various organs.
A pulse oximeter is a tiny device that usually slides over your fingertip or clips on your ear lobe and uses infrared light refraction to measure how well oxygen is binding to your red blood cells. Oximeters report blood oxygen levels via an oxygen saturation measurement called peripheral capillary oxygen saturation, or SpO2
Dr. Connolly: If a person has a mild case of COVID-19 and is self-treating at home, an oximeter can be a helpful tool for checking oxygen levels so that low oxygen levels can be caught early. In general, the people who are theoretically more at risk for oxygen issues are those with pre-existing lung disease, heart disease and/or obesity, as well as active smokers.
In addition, since "happy hypoxia" can be present in people who might otherwise be regarded as asymptomatic, a pulse oximeter can help ensure that this clinically silent early warning sign is not missed.
If you have tested positive for COVID-19 and are concerned about any developing symptoms, check immediately with your health care provider. From a lung health standpoint, aside from the objective pulse oximeter measurements, I suggest to my patients that if they're having any labored breathing, severe chest pain, uncontrollable coughing or dusky lips or fingers, it's time to go to the ER.
For a person with COVID-19, when do oximeter measurements become concerning?
Dr. Connolly: There is not one, universal SpO2 number indicating that a person's oxygen levels are healthy and ideal.
For an oximeter to be an effective tool, you'll first need to know your baseline SpO2, and keep in mind that your baseline reading can be impacted by pre-existing COPD, heart failure or obesity.
Next, it's important to know when a change in your SpO2 reading becomes significant. An SpO2 of 100% has effectively zero clinical difference to a 96% reading.
As a good rule of thumb, a person with COVID-19 monitoring his or her clinical status at home will want to ensure that the SpO2 reading stays consistently at or above 90 to 92%. If the number consistently drops below this threshold, timely medical evaluation is warranted.
What might make pulse oximeter readings less accurate?
Dr. Connolly: Pulse oximeters can have falsely low readings if a person has circulatory issues with poor blood flow to the extremities, such as very cold hands, intrinsic vascular disease or Raynaud's phenomenon. In addition, fake nails or certain darkly colored nail polish, such as black or blue, can distort the readings.
I always recommend that people measure at least one finger per hand to confirm the number