Thursday, 13 October 2016

Why bronchiolitis doesn't get better with inhalers and how understanding "why?" is better than "do that!"

There was interesting debate this week about using inhalers for bronchiolitis.  The interesting features included how heated it became (there was mild name calling and much "prove it" involved, rated PG) and how confident people were in expressing their views on social media about their differing clinical practice.  (Take it from me that you should be fairly sure of yourself before you put something out onto the interweb.)  To me what was most interesting was that the views, despite being polar opposites, where seen as fact.  I am going to assume that all involved want to practice the best possible medicine, but someone must be wrong mustn't they?

What do the guidelines say?  The American Academy of Pediatrics and the UK's National Institution of Clinical Excellence along with other institutions, have produced guidelines in the past few years, specifying that beta agonists and ipratopium should not be used, so why are such debates still happening?  I think that there are a few reasons.  One of these is that for medics, knowing what to do is not as powerful as knowing why, especially when it comes to changing practice.  For me, understanding a disease is much more effective as a learning process than being told, "This is the disease and this is the treatment."   I suppose it is because I already understood the reason why I was doing what I was doing (even if the understanding was flawed), so a diktat is not as powerful a persuader as a new and better understanding.

There is a perpetuated myth regarding beta-receptors and infants.  This myth comes from early studies that failed to find evidence of beta-receptors in infants.  Since then, (as early as 1987) research of better methodology (3) has proven that these receptors are there from birth.  The myth persists because (just as the news reports plenty of crises but not so many resolutions) we are often told things, but rarely does anyone untell us something.

Perversely, the beta-receptor folklore has done us no favours when it comes to trying to understand bronchiolitis and viral wheeze.  The uncertainty created by this myth makes clinicians think that a lack of beta receptors has caused the lack of response to salbutamol.  In fact, the child would respond just fine if only they had bronchospasm.

In bronchiolitis, there is no bronchospasm so salbutamol does not help.  In viral wheeze, ipratopium is a poor treatment and the old myth about ipratropium leads some to believe that ipratropium is the first line treatment for this age group when what they really need is plenty of salbutamol if they really do have bronchospasm.

When discussing the management of wheeze in infants, I often get the impression that people believe that bronchiolitis is just what you call viral wheeze in a child under the age of 12 months.  In fact this is not true.  Bronchiolitis is a separate entity, with different histopathology and a unique clinical pattern of illness.  There is a gradual unset of symptoms, peaking at day 3-4 and beginning to resolve at day 7-10.  Doesn't sound very spasmy does it?

Of course the confusion arises from the fact that both bronchiolitis and viral wheeze are caused by a viral illness.  They can both occur in a child around the age of 12 months old and they cause similar symptoms.  There is however a subtle but helpful difference in the way that they present.

The reason for this difference is a difference in mechanism.  While bronchiolitis and viral wheeze share a cause, the pathology is different because the effects on the airways are different.

I suppose that since it is unrealistic to think that all uncertainty can be removed, the question remains, what is the harm in trying a bronchodilator in all every case, just in case?  Here are a few possible reasons why it is going to make things worse if it isn't going to make things better:

It's always difficult when two illnesses have so much overlap, but there are genuinely good reasons to avoid unnecessary treatment for bronchiolitis.  Hopefully understanding why bronchodilators don't work helps the thinking clinicians to decide for themselves, rather than just being told what to do by guidelines.

Edward Snelson

Disclaimer:  I would like to express my appreciation to the children who allowed me to perform lung biopsies on them during their wheezy episodes.  Science thanks you.

  1. Clinical Practice Guideline: The Diagnosis, Management, and Prevention of Bronchiolitis, American Academy of Pediatrics, October 2014
  2. NG9 Bronchiolitis in children: diagnosis and management, NICE, June 2015
  3. A Prendiville et al., Airway responsiveness in wheezy infants: evidence for functional beta adrenergic receptors, Thorax. 1987 Feb; 42(2): 100–104.