Oxygen saturation as a vital sign

Following the covid pandemic, it’s probably fair to suggest that everyone is a bit more aware of the importance of oxygen. Vital signs are “critical indicators of a person’s health and current medical status”.1

Traditionally, clinicians were interested in four vital signs:

  • Body temperature
  • Pulse (heart rate)
  • Respiratory rate (rate of breathing)
  • Blood pressure

However, more recently, oxygen saturation has been added to the list to become the fifth vital sign.2

What is oxygen saturation?

Oxygen saturation, often abbreviated to SpO2, is a measure of the level of oxygen in your blood. Normally, it should be between 95% and 99%.3

It’s an important measurement because it can show whether your heart and lungs are supplying enough oxygen to vital organs – including your brain.4

Under certain conditions, oxygen levels can fall, and that can cause serious problems. For example, if you suffer from a condition or disease that affects your lung function, that can impact the capacity of your red blood cells to carry enough oxygen.4

Exercise can also affect blood oxygen levels because oxygen is needed to turn food into fuel to keep you going. The harder you exercise, the more oxygen your body needs. That’s why you breathe harder when you exert yourself.5

How is oxygen saturation measured?

Fortunately, measuring oxygen saturation is very easy – so easy you can do it yourself, with a pulse oximeter.

A pulse oximeter is a small device that usually clips onto your finger and passes light through one side of your finger onto a light detector on the other side. As it passes through your finger, the light hits your blood cells and reacts differently to the cells carrying oxygen, compared to the cells not carrying oxygen.

The characteristics of the light that makes it to the photodetector tells you how much oxygen is in your blood.

If you’ve ever been in hospital as a patient or a visitor, you may have noticed that pulse oximeters are commonly used – which once again shows how vital a measurement oxygen saturation is. In fact, a pulse oximeter may have earned its place next to the thermometer in your first aid kit.

They’re a very affordable and easy way to monitor the fifth vital sign. Check out the Heart Sure Pulse Oximeter here.

Always read & follow the instructions for use & health warnings. Consult your health professional to evaluate the readings.


  1. https://www.sciencedirect.com/sdfe/pdf/download/eid/3-s2.0-B9780721603612500259/first-page-pdf
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1304215/
  3. https://exercise.lovetoknow.com/about-physical-fitness/understanding-blood-oxygen-levels-during-exercise
  4. https://www.webmd.com/lung/pulse-oximetry-test
  5. https://www.blf.org.uk/support-for-you/how-your-lungs-work/why-do-we-breathe



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