Sunday, 16 August 2015

The TPR paradox - how do I know if a child might have sepsis?

When I assess an ill child, I am primarily making a decision about whether the child has possible sepsis.  To a certain extent, everything else is detail.  The sepsis question determines which door the child leaves through.  Just like in primary care, I send the vast majority of children presenting to the ED back out the way they came, whether they have pneumonia, urinary tract infection or just a cold.  A small number of ill children are admitted, with the possibility of sepsis as the primary reason.  The question is: How do I decide which door to send each child through?  Once you answer that, I believe that you can begin to understand how to use the many guidelines and decision tools designed to help us make this choice.

In 1935, Einstein and two of his buddies published a paper detailing some problems with quantum physics theories.  In effect they were saying that their own advances had explained a lot about how physics worked, but that there were some things that they could not explain.  Specifically, when two particles went through two doors, one of them did something that didn't make sense.  You could do something to one of the particles and the other reacted even though they are not connected.  This is called the EPR paradox, after Einstein, Podolsky and Rosen.  These three were the best scientific minds in the world and yet they had a missing piece of the jigsaw so big that it called everything else into question.

I believe that we are in a similar place in medicine when it comes to recognising possible sepsis in children.  Once again we have two doors and sending children through these is not as straightforward as it should be.  We all do our best to send each child through the correct door.  There is a big piece of the jigsaw missing though and that’s got us all scratching our heads.  The missing bit is knowing how to go from considering possible sepsis to diagnosing probable sepsis without resorting to reading tea leafs or other substitutes for a valid test.  Most of the time we do our best and accept that in the absence of a good test all we have is good judgement.  The problem comes when a child dies of sepsis and that gap in the process comes under scrutiny.  I'm all for completing the puzzle but I am suspicious that we are trying to put the wrong piece into the gap.

If I asked you to create a decision tool for clinicians to move from considering sepsis to a provisional diagnosis of sepsis, what would you choose as predictors?  You could use the appearance of the child but that is difficult to quantify.  What seems far more reliable is TPR (temperature, pulse and respiration) since these can be measured.  The trouble is that the most measurable features of your assessment are the least reliable.

Before I get a rush of people saying that I think that you should ignore tachycardia and high temperature, please be clear that I don’t think that.  It is just that I think that there is a much better category of evidence and that numbers are not as reliable as we want them to be.

There are plenty of reasons to mistrust numbers.  For starters we have a lack of reliable reference ranges.  There is a good reason why no-one has started making a lot of money out of selling centile charts of paediatric heart and respiratory rates.  They don't exist.  There is not enough evidence to produce such a thing.  The variables are just too many.  Is it age that determines heart rate or your weight?  If it is weight then is it lean weight?  What is the effect of anxiety on heart rate?  How different is a normal heart rate in a resting child to that of a playing child or a screaming child?

What about those normal ranges that you have somewhere when you need to check?  Aren't they evidence based?  You could try to find out what their evidence base is but I could probably save you a lot of hassle by telling you that all the normal ranges that I know of are based on consensus, which is why they are all slightly different from each other. In the past few years, two large analyses have shown that some of the most commonly available reference ranges map poorly to population studies.  Even then, these publications acknowledge that the populations studied are never truly normal. (1,2)

However, I think that this whole issue is much simpler than all of that, because the wrong question is being asked.  The question is not, “Does this child have sepsis?”  The question is, “Can I say with confidence that this child does not have sepsis?”  When we use the rule out rather than rule in approach, everything starts to fall into place, including the value of numbers.

I said before that there is more reliable evidence than temperature and pulse.  That evidence is something that you rely on every time you assess a child and it is the thing that makes sense of the numbers for you: activity.   What we really want to know about the heart rate and capillary refill is not the absolute number but the effect that these are having.  What we need to assess is oxygen and glucose delivery to the organs and there is no better measure of this in a child than what the child can do once these get there.

There is one more variable which complicates the TPR paradox, which is the up and down nature of the illness.  You may see the child at their worst or possibly their best.  In any viral illness the likelihood is that the child will have extremes of activity making nonsense of the assessment.  Thankfully we have two saving graces here.  The first is that we can hear about what has gone before.  The second is that we are able to continue the assessment either by observing, referring or safety netting.

So let’s bring all of this together.  There are two simple elements to recognising serious infection in children.  The first is a hierarchy of evidence.  The second is a rule-in/ rule-out approach.

The hierarchy of evidence is logical.  If I see a child in a playground climbing up to go on the slide and their parent mentions that they have had a temperature, I don’t worry that they may be septic.  I do imagine that they have a significant tachycardia but this will be a result of their activity and possibly their temperature.  I see with my eyes both the activity and the vigour with which it is undertaken.  I don't need to ask any questions or measure any physiological parameters because I have all the evidence that I need.

If I was giving telephone advice and I hear that a child is sat playing on a tablet I now have some very useful information about the adequacy of their brain’s perfusion and oxygen/glucose supply.  It's not as good as what I see because I can't scrutinise what I am being told with my own experienced eye.

Finally if I measure a child’s heart rate and capillary refill, I have information but it needs to be put into context.  Was it cold outside?  Have they just been upset by something?  So the numbers are important but I need what I see and hear to make sense of them.

In any acute assessment of an unwell child this hierarchy can be combined with a rule-in/ rule-out approach to answer the question, “Am I certain that this child does not have sepsis?”

If what you see, hear and measure is all reassuring then the answer is yes, they do not have sepsis.  If what you see, hear and measure are all concerning then the answer should be no, they could well have sepsis.  If what you see, hear and measure give a mixed message then the question remains open and there are various ways to answer it.  Using the hierarchy of evidence above, I feel confident to give paracetamol and wait when a child looks well and behaves well even if they are febrile and tachycardic.  The options are always the same: discharge with safety netting advice, observe, discuss or refer.

Just like the scientists of 1935, none of us has all the answers.  None of the decision tools available is even close to perfect and all of them rely on someone at some point taking responsibility for making a decision about which door the child will go through.  Thankfully the majority of children answer the question for you.

Edward Snelson

If you liked this you might also like:

In Praise of Doing Nothing (Easter Egg – good safety-netting and saving lives)

Or How special is your patient? - (Neonates and other patients who don't follow the rules)



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