Tuesday, 15 March 2016

Croup - proof that a number is never enough information

Croup has to be one of the easiest upper respiratory tract infection diagnoses to make.  You can literally hear the child coming.  The classical croup picture is one of a child who has a cold for a few days and then develops a cough that sounds like a seal.  Although there are differentials listed in the textbooks these can also be excluded clinically:

  • Inhaled foreign body - has not inhaled a foreign body
  • Bacterial tracheitis and epiglottis - child does not look that unwell and is able to swallow their own saliva

So, it is a simple case of, "this is croup!"  The next job is that you have to ask yourself how bad the croup is.  The good news is that there are scoring systems available.  The problem with scoring systems is that they create the impression that the game is over.  It really isn't.


If you do use a croup score, you should see it for what it is: a snapshot which attempts to quantify what you see and hear.  As is often the case, these scoring systems are developed for the purposes of research and have been adopted into clinical practice.  It is equally valid to take the signs and symptoms and qualify these into a mild, moderate or severe croup.  You might find a scoring system helpful but it is not mandatory.  Whether you use a qualitative or quantitative method, the severity is only part of the picture.

One thing that guidelines often struggle to emphasise well is the importance of the trajectory.

All three children in the figure above have a Westley croup score of 4 when seen by a clinician.

Child A was found in the morning with a stridor and significant respiratory distress. As often happens, when the parents rushed the child to be seen, child A improved and now has the tail end of a soft stridor.


Child B was coughing, had a soft stridor all night and refuses to move out of croup limbo.

Child C was not so bad when they set off to see you but has got noticeably worse in the time leading up to the consultation. The game is just beginning for child C.
The score (or your qualitative mild/ moderate/ severe assessment) and the trajectory are the most important factors. I would also consider risk factors including co-morbidities and previous life threatening episodes of croup.

That brings us to croup management-

Turbulent flow of air creates more than twice as much resistance as laminar air flow. Children who have croup will tend to position themselves and breathe optimally if left alone to do so. Distressing the child either directly or via the parent can cause sudden decompensation.


If the child is in the severe category then facial oxygen should be given followed rapidly by nebulised adrenaline (epinephrine). Doses as per your formulary but at the time of writing that is 5mg for a child 2 and up where I work.  If not already at hospital, a child with severe croup should be moved there quickly. If already in an ED then the child may need further escalation but in many cases the adrenaline will buy time and avoid the need for airway management.


For mild and moderate croup the best evidence is for systemic steroids.(1)  There is evidence that dexamethasone is more effective than prednisolone.(1) Studies have also compared different doses of dexamethasone and found that there is no difference between giving the larger dose 0.6 mg/kg and the smaller dose 0.15mg/kg.(1) I have been using the lower dose for many years but have no hesitation in repeating the dexamethasone if the child vomits afterwards and it is uncertain as to whether the first dose stayed down.


Be warned, my GP land colleagues: dexamethasone liquid can be difficult to source from community pharmacies. NICE says that "Providers of urgent care services should ensure that dexamethasone is available."(2)  This may not be within your control.  Unless you know that your patients can get it easily, prednisolone may be the pragmatic choice.


I am very aware that treating mild croup is a relatively new phenomenon. If you fear change, please take comfort in knowing that I do too. However my dislike of medicalising childhood illnesses does not extend to croup. This is for two reasons. The first is to do with the aforementioned trajectory. I don't know which mild croups are going to become moderate or severe but some will and theses children may become victims of another fact of science.

The flow of air through a tube is reduced by the reduction in diameter to the power 4. If a child with croup gets worse and their airway haves in diameter then they will only be able to shift one sixteenth of the air. If that air flow becomes turbulent then you won't need a score to tell you how bad they are. So mild croup is not a thing to dismiss. It is level one of the game of croup. Level 1 is deceptively easy but unlike most games, level 2 is much harder and level 3 completely unexpected.


Edward Snelson
@sailordoctor

Disclaimer: It's not a game.

References:

  1. Cochrane library review, Glococorticoids for croup
  2. NICE, Clinical Knowledge Summary for Croup







2 comments:

  1. Great article thanks. Andy EM reg UK

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  2. Great Blog Sir,

    I concur with you, Turbulent stream of air makes more than twice as much resistance as laminar wind current.

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