Making a diagnosis is a complex business. It is such a complicated process that, most of the time, we don't really think about it at all. This has been described as type 1 thinking (intuitive) in the context of clinical diagnosis. (1) Most days, I do very little thinking. When I come across something unexpected or unfamiliar, I am forced to come out of this unconscious automatic mode and think carefully and consciously (type 2 process) about what is going on. I have to engage my cortex, and it hurts.
So, going back to this little scenario. Let's say that the child is 2 years old and has has a cold for 3 days. They are brought by his parents because they have noticed that his breathing is a little fast. He looks well and is really quite happy with the toys in your room. Snot bubbles from his nose as he comes and sits on his mother's knee. Looking at his chest, he has mild subcostal recession and a mild tachypnoea. When you listen to his chest, you hear... breathing.
So, what most people do in this circumstance is to listen some more. It is traditional to check your stethoscope for gremlins or signs of tampering before pushing the earbuds a bit harder into your ears before listening again. However, there is no getting away from the fact that there is no wheeze, nor is this the silent chest that is so feared in asthma and viral wheeze. In a silent chest, no breath sounds can be heard and the patient looks awful. This child has breath sounds and looks well.
The reason that it causes us to have a confused moment is that there are certain combinations of signs and symptoms that indicate a particular illness. That is particularly useful in children's respiratory illnesses since no one sign or symptom is likely to be specific to an illness. This is why cough and fever do not equal a lower respiratory tract infection. We need to look for the presence or absence of other features to form a likely diagnosis.
So what we've got now is a mystery illness. What causes a well child to have respiratory distress without a wheeze or stridor?
What will probably happen next is a little surprising the first time you experience it: a wheeze appears. More importantly, the child's breathing improves. So, what is going on here?
The answer to that would be science. Science and music are happening and it goes like this: In order to have a wheeze, there must be the correct conditions for this to occur. A musical note needs the right amount of air flowing through a tube in the right sort of way. The size of the tube matters quite a lot. Ask any wind musician or organ player.
In these cases there is bronchospasm (caused by viral infection) but the conditions are not right to produce a wheeze for you to hear. Of the parameters that affect the musical note (length of tube, diameter of tube and flow of air) you can change two with β-agonists. You can't change the length of the tube but the other factors should respond nicely.
So, if you don't like what you hear, change the tune. When your clinical diagnostic brain tells you that there should be a wheeze, you are probably correct. If you were expecting a wheeze but don't hear one, by all means rethink your presumption. If you are left with the same conclusion, then try the β-agonist trick. It works a treat.
Disclaimer: This is a very different thing from rechecking a blood pressure until you get the number that you want. Very different. Anyway, I would never do that.
- Croskerry P, A universal model of diagnostic reasoning, Acad Med. 2009 Aug;84(8):1022-8.