News : Pulse oximeters


In 2018 we were asked to look at the use of pulse oximeters in the mountains. Here's a summary of our findings after reading through the literature on them;

Pulse oximeters- Just how useful are they?

They are small, portable, getting cheaper and used increasingly on high altitude treks. They work best at or near sea level so can cause confusion when used in the mountains. This article aims to help you understand them better and how and when to use them.


What causes altitude illness?

It’s thought altitude illnesses affects some people at high altitude because of the way the body reacts to lower oxygen levels.

How do Pulse oximeters work?

Pulse oximeters shine light on the finger nail and from the reflection they calculate how much oxygen is carried by haemoglobin in the blood. The result is displayed as a percentage, the higher the number is means there’s more oxygen in the blood, which is vital for life.

Be careful though. Just because a reading might be lower than you expected, it does not mean the casualty will definitely develop altitude illness. 

Also, we cannot be certain what readings are ‘normal’ for a particular place or height as many things affect readings.


These include;

-Bad weather

-Seasons – generally lower readings in the winter

-The quality of the device – some are more reliable than others.

-Temperature – each device will work best between certain temperatures, this information is usually in the instruction manual. 

-Readings below 70%-75% even on a highly accurate probe are likely to be unreliable.

-Cold fingers, nail polish, acrylic nails, very dark skin, and strong sunlight also affect accuracy.

-People vary in the speed at which they acclimatise, so one person might have high readings shortly after arriving at a new altitude and another person may feel well but take a day longer to get up to the same readings.


How to take a reading?

 Readings can go down if you’re talking and up if you breath quickly.

Therefore, the best way to check saturations should be as follows;


after several minutes of rest

at least an hour after meal times

with no talking by the casualty 

the casualty has warm fingers 

record your readings once the figures have settled for at least 15 seconds


When to use a pulse oximeter?

Do not to routinely measure oxygen saturations when feeling well as it is likely to cause more worry if it's lower than expected. Only check them when someone’s feeling unwell above 3000m. 


What’s a normal reading and what if you get a low reading?

The reading is probably going to be less than 96%-98% (the usual range at sea level). Check a few readings in other healthy individuals at the same altitude. If it’s lower than any of theirs then be alert to the possibility that the casualty may be are suffering from an altitude related illness e.g. HAPE. Do not forget to take into account the person’s symptoms and physical conditionIf they do not improve with descent and/or oxygen/or a Portable altitude chamber, then re-consider other causes such as pneumonia, pulmonary embolism, pneumothorax and heart attack.

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