JC: Don’t Write off the Respiratory Rate – Part One

2

Two really interesting PEM-relevant papers appeared online first in Archives of Disease in Childhood in July – and happy days, both are FOAM!

What’s great about these papers is how they compliment each other in thinking about paediatric respiratory rates. You’ll often hear respiratory rate reported as the forgotten vital sign, its significance overlooked.

But exactly how useful is it as a standalone marker of underlying pathology? Let’s have a look at the two papers, the first in this post and the second in a post coming later this week.

The first paper I think you should look at is this one. Two authors – a paediatric respiratory specialist and a paediatric cardiologist – take us through a clinical approach to the child with an unexplained raised respiratory rate. You can find a PDF of the paper here (or click the graphic below). The paper isn’t very long and it’s pretty easy to read so I recommend you have a look at the original article.

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I have occasionally seen children brought or referred (usually by a GP) to the ED with an isolated, unexplained tachypnoea. More commonly we see children who seem reasonably well for whom the respiratory rate remains elevated. The article isn’t really concerned with those patients – more with persisting tachypnoea in the absence of other signs of disease.

What This Paper Doesn’t Do So Well

It’s not immediately clear what constitutes a “baby” in the authors’ minds. There’s a reference to a particular piece of hardware being suitable for use up to 18 months of age, while a graph of “normal” respiratory rates with centiles gives values up to 12 months. The majority of the manuscript seems to talk about findings up to the age of 12 months but it would have been nice to clear up that ambiguity; while the term “infant” is generally understood to refer to the first year of life, what is a baby?!

What This Paper Does Well & What You Should Do

The paper takes us through a number of important points in assessing children with a raised respiratory rate.

1. Apparent tachypnoea can be a normal finding

Infants rarely demonstrate a completely regular and predictable respiratory pattern – as new parents will tell you. Often they exhibit “periodic breathing” – rapid, shallow breathing interspersed with apparent apnoeic episodes lasting a few seconds (<6 secs). This pattern is not associated with colour change and it most often observed when the baby is asleep, usually disappearing by 6 months of age.

2. Reliable measurement of respiratory rate is hard

I have always found measuring the respiratory rate ridiculously difficult. Clearly nurses who can do this by visual inspection alone possess magical powers (I think all nurses have magical powers anyway); I can’t, so if I want to measure a respiratory rate I use a stethoscope. The authors also remind us of the inconsistencies inherent in counting for 15-20 seconds and multiplying up. If you want a reliable measure, use a stethoscope and listen for a full 60 seconds.

3. Examine carefully; look for clues of underlying pathology.

This means a full cardiac examination (including palpating femoral pulses, liver edge and the “murmur of a cerebrovenous malformation”, heard by auscultating the occiput – I’ll admit, that’s a new one on me) and respiratory examination. Think about neurological causes (development history and assessment of tone) as children – not just infants – are highly reliant on diaphragmatic function to breathe effectively before the thoracic bony structures calcify and intercostal muscles become stronger.

Think also about physical causes – choanal atresia (congenital blockage of the posterior part of the nasopharynx) is usually obvious from birth (as neonates are obligate nasal breathers, as Iain Beardsell likes to remind us)

4. Utilise investigations to rule out serious pathology – but follow-up

The authors go on to list a variety of conditions which may manifest as tachypnoea in an infant. As an ED physician you probably don’t need to know about the rarer conditions, but you do need to appreciate that tachypnoea can be the first sign of some rather serious underlying conditions and that while for many children the tachypnoea will resolve before a full explanation is uncovered, some will require specific treatments. There are some red flag signs and symptoms the authors have identified which are depicted below.

Journal club at st emlyn's-4

In the absence of these red flags (i.e. a well child with tachypnoea), the authors advocate three main investigations, all of which would be appropriate in the ED.

SpO2

Checking SpO2 is vital: remember, pre-ductal sats are measured using the right hand (this recent paper suggests you might be able to use the left hand); and a leg for post-ductal sats. SpO2 should be >94% according to the authors, who reference this paper which states that the median SpO2 in the first year of life is 97-98% and although the SpO2 does vary in babies  in only 5% of under 1s is the SpO2 <90% for more than 4% of the time.

Hyperoxia Test

If the SpO2 is <85%, consider performing a hyperoxia test – give the patient high flow O2 (100% via non-rebreathe mask) for 5-10mins. In reality I think you’d be hard pushed to stop the nurses from doing this anyway in an otherwise healthy child with unexplained low SpO2! What you expect to see is a correction of the apparent hypoxia; if there’s no change then it’s highly likely that there is a right to left shunt underlying and the child needs a cardiology review. The authors advocated pairing the hyperoxia with arterial blood gas sampling but certainly in the UK that’s rarely something we do in children, let alone infants.

Chest XR

As much as we try to avoid unnecessary radiation in children, a chest radiograph is going to be useful; a normal chest x-ray is reassuring while it may expose underlying abnormalities including occult pneumonias (I’ve seen this in clinical practice) and strange cardiac shadows to guide your management of the child.

And… BM, Cap Gas & ECG

These three investigations are quick and potentially really useful; I would personally add a blood sugar, a cap gas and an ECG.

The youngest DKA I’ve seen in PED was under two years of age and presented with an unexplained tachypnoea.

Perhaps I’m biased having worked at a metabolic centre, but metabolic disease can be hard to pick up unless you look for it – and the capillary gas will give you lots of extra information (often including the blood sugar).

And yes, I’d ask for an ECG having seen an infant present with an apparently normal heart rate but increased respiratory rate (and poor perfusion): note the ECG machine calculated heart rate here and then work it out yourself. The monitors agreed with the ECG’s auto-read of the rate but the rate was clearly not 164/min… After I got over the initial confirmation bias, the heart rate responded nicely to some adenosine!

MottledBabyECG

Follow-Up

Lastly, even if all these things are normal, the authors say we can discharge these patients home but need to ensure they have follow-up; they suggest both paediatric cardiac and respiratory clinics, within four weeks with advice to return in the interim if the situation changes. It’s worth considering how easy access to these tertiary services is for your from your ED – a general paediatric clinic may be easier to access but they may do little more than you’ve already done if you’ve followed the authors’ approach.

Stay tuned for the second respiratory rate paper!

Nat

Before you go please don’t forget to…

 

Posted by Natalie May

Dr. Natalie May, MBChB, MPHe, MSc, PGCert Medical Education, FRCEM, FACEM is section lead for paediatrics and medical education. She is an Editorial Board Member of the St Emlyn’s blog and podcast. She is a specialist in Emergency Medicine (Australia) and a Specialist in Emergency Medicine with Paediatric Emergency Medicine (UK). She works as Staff Specialist in Prehospital and Retrieval Medicine with the Ambulance Service of New South Wales (aka Sydney HEMS). She also works as aStaff Specialist, Emergency Medicine, St George Hospital (South Eastern Sydney Local Health District). Her research interests include medical education, particularly feedback; gender inequity in healthcare; paediatric emergency medicine. You can find her on twitter as @_NMay

  1. […] now we know what to do with an unexplained abnormal respiratory rate in a baby – but how do we know what constitutes an abnormal respiratory rate? That’s the question […]

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  2. […] two part series on the importance of the respiratory rate from St. Emlyn’s – Part 1 + Part 2. […]

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  3. […] two part series on the importance of the respiratory rate from St. Emlyn’s – Part 1 + Part 2. […]

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