Pulse oximeters

Pulse Oximeters – Are they useful in daily life A personal view by Ashley Hulme Although I have done my best to check my facts and comments, please be aware that I am not a medical professional. I hope that my comments are useful should you wish to obtain your own oximeter, but by all means do your own checking and if in any doubt please check with your own doctor before making any important decisions based on what I say here.

What are oximeters used for?

They are a simple, low cost device to measure the amount of oxygen carried in the blood. They vary from small finger-tip devices to professional desktop units. The result is given as % SpO2.

There are four basic types: • Fingertip pulse oximeters • Handheld pulse oximeters • Wrist-worn pulse oximeters • Table-top/Bedside pulse oximeters Some provide more information or maybe record information over a period of time.

What is SpO2 The objective is to obtain a reading of the level of oxygen saturated in the blood, i.e. the percentage of haemoglobin molecules in arterial blood saturated with O2, this is reported as SaO2.

• Readings vary from 0 to 100% • Range from 94 – 100% in healthy adult SpO2 means the SaO2 measurement as determined by pulse oximetry. Measurement of oxygen saturation level using pulse oximetry is not quite as accurate but is very simple and good enough in most cases.

• Measurement of SaO2 requires a sample of blood.

• Measurement of SpO2 is simple and convenient.

How Does Pulse Oximetry Work?

LEDs shine red & infrared light through tissue

• • •

Oxygenated haemoglobin absorbs more infrared light Deoxygenated haemoglobin absorbs more red light SpO2 calculated by comparing the amounts of red and infrared light

Pulse oximeters should be used on a fingertip, toe or earlobe. Clearly the fingertip is easiest for most of us.

What do I use mine for?

To check that my SpO2 level does not go too low when exercising, etc.

• Out walking • In the gym • Working at home • To avoid going below 80% (better to stay above 85%) • To target remaining above 90% If SpO2 <85% – is oxygen required?

When first using mine in a gym on a treadmill, my SpO2 level was going down to 78% and it was recommended that I use oxygen in the gym. I do not like the gym and prefer walking (for example) at a NT property such as Kingston Lacy. However, it has been recommended that I take oxygen there if I am intending to walk out for any distance. I tend to walk quite quickly, which drives down my SpO2 level.

Don’t be ruled by it Also go by how you feel. Sometimes, when feeling breathless, the reading is >90%. Or, when feeling OK, the reading is <90%.

The reading is not an absolute value. Most pulse oximeters have an uncertainty of ±2(%) and they can be affected by other influences.

If you see a reading of 94% it could actually be 92% or 96% At 94% this is not too important, but if you see 78% then it could actually be 76% which could be of concern.

Also, they all only work between 70% and 100%.

Other things to be aware of It may not work or be accurate if • Your finger is too cold • You have nail varnish • The unit does not fit correctly • Too loose or too tight • Light interference (very bright conditions) • Movement (such as shivering) All these can affect measurement. On one occasion I arrived back home after walking quite quickly to shops and back. My hands were cold and my oximeter refused to give a reading until they had warmed up a bit.

Choosing a Pulse Oximeter Finger-tip units most convenient for personal domestic use • These vary from £12 to >£100 • They are all specified with the same or very similar accuracies • NHS document (CEP10066 – 2010) shows that not all have been proven I obtained several samples to compare how they performed.

Comparison of low cost oximeters 1 2 3 4 5

SpO2 PR SpO2 PR SpO2 PR SpO2 PR SpO2 PR

95 81 95 81 99 70 88 93 98 70

95 77 96 77 99 40 99 76 99 38

95 75 95 82 97 59 98 73 97 72

93 84 93 84 94 83 93 80 -

91 94 92 95 92 93 94 82 90 82

94 80 93 80 97 84 98 80 99 46

91 91 92 91 94 90 97 85 -

93 82 93 84 95 83 97 73 99 48

93 87 93 85 96 83 97 79 98 53

95 75 95 74 97 75 97 74 96 77

91 95 92 94 94 86 99 76 99 51

92 87 93 87 95 86 96 84 92 69

82 121 81 169 81 123 85 116 81 92

92 88 93 89 94 84 97 85 98 77

94 88 94 89 92 88 94 86 -

94 85 94 85 92 86 97 82 -

94 86 93 87 92 85 97 84 -

Note: PR = pulse rate Green shows readings of SpO2 that are reasonably in agreement, allowing for unit accuracies.

Blue shows readings of pulse rate that are reasonably in agreement, allowing for unit accuracies.

Red shows obvious significant differences.

Black shows other results that may be OK but difficult to rely on. They appear to me to be a bit optimistic.

It is important to remember that this not a scientific study in a controlled environment, but just some comparison tests I performed at home. I used all 5 on my fingers at the same time to get a reasonable comparison. I have noted that the oximeter I use every day (number 1 in the table) reads consistently 1% lower than a unit in Southampton hospital, which is well within the published accuracy.

Unit Make

Model

Made in Price

Comments Checked by clinical trials Seems reasonable OK if used with caution Always shows 98% on switch on Unconvinced about quality Always shows 98% on switch on Failed display (dim) after 2 days

1 2 3 4

Nonin Contec (Risling) Risling

GO2 CMS-50DL RPO-8A RPO-8B

USA China China China

£78.00 £17.29 £12.99 £11.99

5

Risling

RPO-8B

China

£11.99

They all need a little time before they give a proper result. The units labelled 1, 2 and 3 all give a blank reading until they are ready to show a measurement.

The units labelled 4 and 5 show 98% for a while before settling down. This could be confusing.

I also felt that the Risling units did not fit so comfortably.

Conclusions I believe that using an oximeter can be useful in daily life, especially when out walking, etc. It can help to make sure you pace yourself or when you should consider using oxygen.

If you do decide to buy one, consider buying a reasonably good unit. My experience shows that the very cheap ones are unhelpful and confusing. Look up CEP10066 â&#x20AC;&#x201C; 2010 on the internet and buy unit with proven specification. The NHS document CEP10066 is easily found on the internet (just google CEP10066). Although it is a little dated it gives a good indication as to which manufacturers take the testing seriously.