Pulse oximetry in babies and small children - Essential ‘fifth vital sign’ or potentially inaccurate and poorly validated technology?

I’m sure we are all preparing ourselves for a potential significant surge in bronchiolitis over this autumn and winter. A past winter of lockdown and reduced social interaction has left many children now going into their second year of life unexposed to RSV and at risk of bronchiolitis. Together with the usual cohort of under ones, there is concern we will see substantially higher numbers of bronchiolitis this year, and has prompted NICE to review and re-publish their bronchiolitis guideline in August 2021 in readiness for this predicted surge. The Royal College of Paediatrics are also pretty twitched about it and in their recently published document clearly want as many children to (safely) be managed in primary care as possible, stating that systems need to be in place ‘to ensure children with mild bronchiolitis and lower respiratory tract infections are managed in primary care settings where possible and to reduce the number of infants and children with respiratory symptoms presenting to hospital’. 

One of the updates to the NICE guideline was around pulse oximetry thresholds for referral, admission and discharge, with the RCPaeds recommending that ‘access to paediatric oxygen saturation monitor probes in primary care should be prioritised’. The recommendation to measure sats in children with bronchiolitis is not new, with the previous 2015 NICE guideline recommending assessment in all children ‘including those presenting to primary care if pulse oximetry is available’. But the updated guideline and push for wider use of pulse oximetry in primary care when assessing bronchiolitis has put this issue in the spotlight, yet concerns remain. I think it’s fair to say there is considerable uncertainty about how useful and accurate oxygen sats are in babies in primary care, with a quick straw poll of the NB team substantiating a range of views!

All of which led us to ask ourselves a number of questions - How accurate are oxygen sats in babies and small children? How reliant should we be on O2 sats levels to guide referral/admission? What are the pitfalls in their use? How comfortable are you in using a paeds sats probe? Do you even have one or know where it is kept?! It’s all very well popping a finger probe on an adult, but trying to get a paeds sats probe on a wriggly crying baby that’s a bit chilly around the edges is considerably more challenging! 

First some very important pitfalls we need to be aware of when using and interpreting sats in babies and small children. Sounds obvious, but we MUST use the correct age appropriate probes. A National Patient Safety Alert in 2018 (highlighted in the NICE bronchiolitis guideline) concluded that if pulse oximeters intended for adult use are used on babies or children, sats levels may read 50% lower or 30% higher than the true level. This was reiterated by a useful review on pulse oximetry by the Primary Care Respiratory Society July 2021 - they recommend that children <2 need specialised paediatric probes/attachments. The other key point they make is that small children are much more likely to have poor peripheral perfusion due to small digits, meaning we may not get true/accurate readings. It is also interesting to note that the Royal College of Nursing document on assessing and measuring vital signs in children does not even have a section on pulse oximetry, which may reflect the uncertainty in this area. 

Any practical tips to help us? A few useful pointers I’ve picked up from colleagues include using the big toe (rather than finger, may reduce risk of poor perfusion in small digit) and use a wrap-around probe attached with some extra tape. Put the probe on at the beginning of the consultation to give time to check you’ve got a good trace/reading and let the child settle. Consider putting a sock back over the foot to keep it warm/reduce the risk of poor perfusion. 

So how reliant should we be on the oxygen sats level? Thankfully this seems to be the one thing that everyone agrees on - oxygen sats are only ONE part of assessing children with bronchiolitis and we must not get overly focussed on this one aspect, to the detriment of a more holistic assessment. NICE (and the RCPaeds flowchart) are quite clear that if other parameters are concerning we should still refer. Ultimately we must not take oxygen sats out of context - we know children can be quite sick, compensating with increased RR and pulse and normal saturations before they quickly fall off the cliff and desaturate quickly. I know many colleagues who regard respiratory rate as a more accurate predictor of a sick child than oxygen saturations. As one of my colleagues succinctly put it, a sick kid is a sick kid irrespective of their sats. Conversely, arguments have also been made that the introduction of pulse oximetry in the context of bronchiolitis has led to over-diagnosis of hypoxaemia, increased referrals and admissions with no improvement in outcomes, leading to potential harm for both individuals as well as hospitals that may struggle with this increased workload. Not a can of worms I’m going to open but for an interesting article see BMJ 2017;358:j3850 from a few years ago, as well as some robust alternative view points in the responses!

Oxygen saturations are sometimes referred to as the ‘fifth vital sign’, and that feels about where they should be - after the 4 traditional vital signs (temperature, pulse, respiratory rate and BP/capillary refill time) and to be used in addition to, not instead of, these four parameters; and importantly they should be used as part of a wider holistic assessment. Measuring oxygen sats in children with bronchiolitis may be a useful adjunct to our clinical assessment, as long as we use them as part of a wider holistic assessment and bear in mind the caveats and pitfalls above. 

References and other useful information:

• NICE NG9: Bronchiolitis Aug 2021
• RCPaeds guideline bronchiolitis July 2021
• RCPaeds flowchart for managing bronchiolitis in primary care (excellent 1 pager)
• Patient facing information on children with wheeze/SOB inc. bronchiolitis (good safety netting document)
• Primary Care Respiratory Society - Caveats with pulse oximetry July 2021