Pulse oximeter is a simple device that uses infrared light to measure the amount of oxygen in your blood—it takes just seconds to do this.
More commonly used in hospitals, a pulse oximeter is simple enough to use at home—all you need to do is put the machine (it looks a bit like a stapler) on your index finger or big toe or ear lobe—whichever is convenient—and turn it on. It gives a reading in SpO2 which is the percentage of oxygen saturation in the blood. A reading below 95% means you should call your doctor.
Let's take a step back to see why and when we need to measure blood oxygen saturation: the haemoglobin in our red blood cells binds with oxygen to take it to different parts of the body. According to the "WHO pulse oximetry training manual 2011", each haemoglobin molecule can carry up to four molecules of oxygen. If every haemoglobin molecule in the body binds with four oxygen molecules each, blood oxygen saturation is 100%. Normally, the oxygen saturation or SpO2 in haemoglobin is 95% or more.
In medical conditions that cause shortness of breath or chest pain and respiratory illnesses like asthma, chronic obstructive pulmonary disease and now COVID-19, however, blood oxygen saturation may drop to or below 94%—this state of low blood oxygen is known as hypoxemia. Patients with hypoxemia need supportive oxygen therapy, which could be given through simple but effective equipment like an oxygen cylinder and cannula/mask, or an oxygen concentrator (which uses oxygen from the air around us and doesn't even require an oxygen cylinder). If unchecked, hypoxemia can advance to a stage where the different organs of the body don't get enough oxygen for normal processes—this condition is known as hypoxia. This is a potentially life-threatening condition in which the patient will definitely need oxygen therapy, and may even need heavy-duty oxygen support through a ventilator or ECMO (extracorporeal membrane oxygenation) machine in a hospital. (The ECMO machine oxygenates the blood outside the body, hence the term extracorporeal.)
A pulse oximeter can quickly alert doctors, caregivers or patients to dangerously low oxygen saturation in the blood or hypoxemia—sometimes even before symptoms like difficulty breathing and cyanosis show up. This can help save precious minutes in getting the necessary therapy to treat hypoxemia and prevent hypoxia. (Cyanosis, or lips and fingers/toes turning blue, may occur in some patients with blood oxygen saturation below 90%. However, doctors warn, cyanosis is quite hard to spot and may not even occur in patients who have anaemia).
Of late, many people have started buying pulse oximeters and with good reason. The COVID-19 outbreak has become associated with what is colloquially known as happy hypoxia or silent hypoxia. Simply put, happy hypoxia is a condition in which the patient does not exhibit any outward signs of low oxygen saturation until the blood oxygen levels drop significantly, at which point the patient may need emergency care. Having a pulse oximeter to periodically check blood oxygen levels could alert people if their oxygen levels start falling.
Conversely, getting a normal reading could also give them some peace of mind that they are not in any immediate danger. (That said, keep in mind that shortness of breath and hypoxia are severe symptoms of COVID-19. Milder symptoms of COVID-19 like fever, cough, fatigue and loss of sense of smell or taste should not be ignored, even if your oxygen saturation levels are okay.)
Read on to know all about pulse oximeters, including how they work and who needs them.
Read more: How to deal with the anxiety of living through a pandemic