Unprecedented Covid cases in Australia have coincided with surging demand for pulse oximeters, as hundreds of thousands of people manage their infections at home.
At-home care guidelines for Covid-19 suggest using pulse oximeters – portable devices worn on the finger – to provide a measurement of oxygen in the bloodstream.
Low oxygen saturation levels may be a warning sign of worsening Covid, and people at higher risk of having their condition deteriorate – such as those who are over 65, pregnant, immunocompromised or Indigenous – may be provided with an oximeter by a local health service.
But a run on pulse oximeters has made buying them difficult, with experts saying they aren’t a necessary device for everyone who is Covid positive.
What is a pulse oximeter used for?
President of the Australian Society of Anaesthetists, Dr Andrew Miller, said pulse oximeters were reliable devices often used during anaesthesia and in intensive care.
“It’s a bit like a thermometer in that … it’s something that can be used at home by a layperson and get a meaningful result out of it.”
The device, which clips painlessly over a fingertip, measures blood oxygen saturation and pulse rate. It works using lights and a sensor that measures the colour of blood, which is brighter red when there is more oxygen in it.
Cheaper oximeters display the measurements as figures, while more expensive models also display a waveform of the pulse in the finger.
Some phones and smart watches have a pulse oximeter function, but the Royal Australian College of General Practitioners has warned that these “are not accurate and should not be used”.
Oximeters can be a useful addition to proper medical care, but not a replacement, Miller said. “We would encourage that they only be used in the context of someone who’s getting clinical support to be at home by either a state hospital-in-the-home service or a general practitioner.”
In the absence of an oximeter, breathing rate can be a good proxy, Miller said. “We’re normally breathing about 12 [breaths a minute]. People who are breathing over about 15 to 20 respirations a minute … we start to get concerned.”
Dr Suzi Nou, an anaesthetist in Melbourne who has been managing Covid patients in the community said: “If you’re having trouble breathing, if it’s an effort to do things like walk up the stairs, if you’re having trouble talking in a complete sentence and that makes you breathless, if you’ve noticed your lips or fingernail beds are going a little bit blue – they would be very strong signs that there’s not enough oxygen in their body.”
Are they accurate?
For those who are able to source a pulse oximeter: an oxygen saturation of 95% or above is the typical baseline for a healthy person breathing at rest.
According to Australian guidelines for people with Covid a saturation level between 92% and 94% at rest is a sign of moderate disease.
“In a non-pandemic world, if I had a patient who is otherwise fit and healthy and a bad chest or viral chest infection with saturations of 93%, I’d want to be looking into that,” Nou said, adding that people with lung conditions such as emphysema or chronic bronchitis may have a baseline level lower than 94%.
“Less than 92%, that is concerning: call an ambulance. Definitely seek medical attention,” she said.
There are certain factors that will help to improve the accuracy of a reading.
The devices are affected by movement – such as coughing fits, as well as poor circulation in the fingers. People with acrylic or gel nail polish should rotate the oximeter on their fingertip – so that it clips over the skin instead of the nail.
Concerns have also been raised about the accuracy of the devices in people with darker skin pigmentation. Earlier this month, the Therapeutic Goods Administration warned that pulse oximeters could overestimate oxygen levels in people with darker skin tones – meaning that low oxygen levels had the potential to be missed in these populations.
“If a state health system was rolling these things out, they need to make sure that they’re using one that’s been validated across ethnicities,” Miller said.
Nou said the jury was still out on how significant an effect skin tone had on oximeter accuracy. “I do a lot of work in developing countries with people with darker skin pigment, and I haven’t been too concerned about the accuracy of them,” she said.
“The monitoring is there to assist your … observation of the patient. So if I think someone is looking like they’re having trouble breathing and the monitor tells me it’s a great number, I’m always more likely to believe the patient.”
Can I still get one?
Nou said anecdotally people had been struggling to source them for personal use. “I’ve had some patients who have been able to get hold of them, so it is variable,” she said.
A spokesperson for the Pharmacy Guild of Australia said members had not reported any noticeable uptick in demand for oximeters since the start of the pandemic.
But only one of 10 chemists Guardian Australia contacted in Victoria and New South Wales said they had any in stock.
One pharmacy worker at a major chain in Melbourne said they had been out of stock for two weeks and were not sure when a resupply would occur. Another said the products were “quite popular at the moment” and that they hadn’t had any available since Christmas.
“Everyone’s been trying to get them,” said a third, while a fourth said their usual wholesale supplier was out of stock.
