My last post was about asthma. This one is about another very common breathing problem in children — bronchiolitis. In some ways it is similar to asthma, but in other important ways it is very different. With winter nearly upon us it’s time to reacquaint ourselves with this common entity.

I’ve written before (here and here) about the reliable seasonal arrival of the virus we call RSV, the chief cause of bronchiolitis. To scientists, RSV is a fascinating virus with several unique properties.

One of these is its behavior in the population. When it is present, RSV is everywhere. Then it suddenly vanishes. There are exceptions to everything in medicine — I have seen sporadic cases during the off-months — but generally RSV arrives with a bang in mid-winter and then leaves suddenly in the spring. It is the only virus that consistently and reliably causes an epidemic every year, although it often alternates more severe with milder visitations. However, RSV epidemics may still have some regional variability. For example, often one city will have a much more severe epidemic than do others in other regions of the country.

Another aspect of RSV that interests medical scientists is how poor a job our immune systems do in fighting it off. Virtually all children are infected with RSV during the first year of life. Not only that, all of us are reinfected multiple times during our lives. Attempts at devising a vaccine for RSV have all been unsuccessful. In fact, early versions of an experimental vaccine seemed to make the disease worse in some infants, raising the possibility that some aspect of our immune response to the virus actually contributes to the symptoms.

RSV has a high attack rate — the term scientists use for the chances that a susceptible person will get the infection if exposed to it. That, plus our generally poor defenses against it, explain the frequent epidemics.

So what is bronchiolitis? What does it look like? In medical terminology, adding the ending “itis” to a word means that whatever comes before is inflamed. Thus tonsillitis is an inflammation of the tonsils and appendicitis means an inflamed appendix. So bronchiolitis is an inflammation of the bronchioles, which are the final part of the system of air-conducting tubes that connect the lungs with the outside world. Beyond the bronchioles are the aveoli, the grape-like clusters of air sacs where the business of the lungs — getting oxygen into our bodies and carbon dioxide out — takes place.

Bronchiolitis, like asthma, is a disorder of blocked small airways. This prevents air from getting in and out normally, primarily out.  But the principal source of that blockage differs between the two lung problems. In bronchiolitis, the main problem is that the bronchiole tubes are blocked from swelling of the walls and from debris caused by the RSV infection — bits of broken airway cells and mucous plugs. Here’s what it looks like.

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Infants are the ones who have the most trouble breathing with bronchiolitis. There are several reasons for this, but a key one is the construction of an infant’s chest. When small airways get blocked, we use our chest muscles — tightening them — to force air in and out of our lungs. We are helped in doing this by the fact that our lungs are encased in a fairly rigid rib cage; when we use our muscles to squeeze or expand our chest the system works like a bellows. Infants can’t do this well because the ribs across the entire front half of their chest are not yet solid bone — they are still soft cartilage.  So when a small infant tries to suck air in against anything that is restricting airflow, like clogged bronchioles, his chest tends to sink inwards, causing what we call retractions. They also have trouble forcing air out, so their chests become hyperexpanded with air. The other reason infants have so much trouble handling debris in their bronchioles is that they are already narrow to start with, so they get more easily clogged up than do larger, adult-sized airways.

How does a child with bronchiolitis look? Typically they are breathing faster than the normal respiratory rate of 25-35; often they are puffing along at 60-70 breaths per minute. They also will show those chest retractions and have a cough. Fever is uncommon. They may look a bit dusky from not having enough oxygen in the blood. They often have trouble feeding because they are breathing so fast. The fast breathing, although with the poor feeding, often makes them become dehydrated. Our breath is completely humidified, so when we breathe fast we lose more water.

Can we do anything to treat this illness, make the symptoms better, make it go away faster? Sadly, the answer is no. I’ve been taking care of children with RSV for 30 years, and I’ve seen a long list of things tried — breathing treatments, anti-viral medicines, steroids, medicines intended to open up the small airways. None of them work very well, if at all. Even though the symptoms resemble asthma in some ways, none of the asthma medicines work very well, although often we try them just to see because the occasional child will get just a little better with them. The research of the past few years is conclusive — the best we can do is to use what we call supportive care and wait for the infection to pass, meanwhile helping breathing as needed with oxygen, clearing the lungs of mucous, and sometimes a mechanical breathing machine in severe cases.

RSV is generally not a serious illness, but for some children it can be life-threatening. These children are very small infants, especially those born prematurely, and those with underlying problems with their lungs or their hearts. For those infants we have a monthly shot (called Synagis) that helps reduce the severity of RSV when they get it, and may even prevent a few cases, but this is not ideal.

Since RSV cannot be prevented, the best thing a parent can do is try to postpone it. That is, if you have a newborn infant in the height of RSV season, try to minimize exposure of your child to people with cold symptoms, especially toddlers. And for those who do handle your infant, have them wash their hands first.