The lung is made up of a branching network of airways, shaped like a tree. The main trunk is called the trachea, with major branches coming off called bronchi. The bronchi then branch into smaller airways, the smallest of which are called bronchioles.

What is bronchiolitis? Bronchiolitis is a viral infection in the lungs that tends to occur in young children under 2 years of age. An infection by a virus causes swelling and increased mucous in the small airways, especially the bronchioles. The peak period for bronchiolitis is in the colder months, usually from November through April in Canada and other countries in the northern hemisphere.

There are several viruses that can cause bronchiolitis. The most common one is called respiratory syncytial virus (rsv). The other viruses that cause bronchiolitis include parainfluenza, influenza, adenovirus, and rhinovirus. These viruses are usually transmitted by unwashed hands infected with nasal secretions and, less frequently, through the air. Infection with rsv is common in childhood, with more than 80 percent of children being infected by the age of 2. Most frequently an older brother or sister or adult with a cold passes the virus on to the baby. The incubation period, that is, the time from when the virus is picked up until symptoms appear, varies from 2 to 8 days.

What does bronchiolitis look like? Initially, the symptoms are similar to the common cold. Often your baby has a runny nose, cough, and a low grade fever. Then symptoms and signs of infection spread to the lungs or lower respiratory tract. His breathing rate increases, as does the apparent work of breathing. His chest appears to be moving in and out faster, the spaces between the ribs seem to be more sucked in, his nostrils may be flaring, and he might make a grunting noise with every breath. There may be general symptoms such as restlessness, lethargy, a low grade fever, and decreased feeding. When listening to the lungs with a stethoscope a doctor or nurse will most likely hear wheezing, crackles, or both.

In babies who are very young or have underlying medical conditions (such as prematurity, chronic lung disease, congenital heart disease, or immunodeficiency), bronchiolitis can result in severe complications. These include apnea, where the baby doesn't take a breath for more than 10 to 15 seconds, or respiratory failure, where the lungs can no longer perform their vital function taking oxygen into the body and getting rid of carbon dioxide effectively.

How do I treat bronchiolitis? The vast majority of infants who have bronchiolitis do not require hospitalization and get better without any special treatment or medications. The disease lasts 1 to 2 weeks, which is similar to what happens when a child has a bad cold. Unfortunately, as in the common cold, there is no specific medication or treatment that makes a big difference in treating babies with bronchiolitis.

If you notice that your child is breathing faster and working hard to breathe, it is urgent that a medical professional examine him. The health care professional will then decide with you whether your infant can be safely looked after at home, or requires specific treatment or observation in the emergency room or hospital.

Several tests can be performed on babies who are suspected of having more severe bronchiolitis. An oxygen saturation level is measured by a monitor attached to the babys finger or toe. This test indicates whether the lungs are doing their job of getting oxygen into the bloodstream. A chest x-ray can be done to look for pneumonia caused by a bacteria or to exclude other disorders. A swab from the nose can be sent to the laboratory to identify the virus causing the infection. This is typically done only in children with bronchiolitis who are seen in hospital.

Supplemental oxygen is required for babies with low oxygen levels generally a saturation level less than 90 to 92 percent. This can be given by a mask applied to the face, through small prongs in the nostrils or, in very young infants, through a clear plastic box placed over their head, a bit like an astronaut.

It is important that your child receive adequate fluids to prevent dehydration. Often young infants may have difficulty coordinating their breathing with swallowing when they are working so hard to breathe, as is the case in bronchiolitis. They may also be exhausted from the effort and the infection, and therefore show minimal interest in feeding. Feeding smaller amounts more frequently may be helpful. However, if feeding is significantly reduced, your child may require intravenous supplementation to provide fluids. Another option would be a nasogastric tube passed through the nostril into the stomach, which can be used to provide formula and fluids.

Chest physiotherapy refers to various ways of tapping on the chest to help remove mucous from the lungs. There is no evidence that this helps in bronchiolitis, and thus it is generally not recom-mended.

There are a number of medications that have been tried with varying amounts of success. Salbutamol is an inhaled medication that works by relaxing the muscular wall of the airways, thereby opening them up. It is very effective in children with asthma. However, in bronchiolitis, although it does seem to be helpful in some babies, there is no convincing evidence that is works particularly well. Many doctors will try salbutamol, see if it helps and if there is no benefit, stop it. Epineph-rine is another inhaled medication. It also works by decreasing the swelling in the airways. Like salbutamol, the studies of its use have produced conflicting results. Some doctors like to use it, while others do not. Both salbutamol and epinephrine are usually given through a compressor in the hospital setting, although salbutamol can also be given at home with a compressor for very young babies or a puffer with a spacing device. Inhaled epinephrine is not given at home.

Steroids work by decreasing the inflammation in the airways. There is no strong evidence that inhaled steroids work in bronchiolitis but some doctors believe that one dose by mouth can help those babies sick enough to come to hospital. Further studies into the use of steroids for bronchiolitis are underway. Ribavarin is a medication that works against the most common virus that causes rsv bronchiolitis. For children with rsv bronchiolitis who have serious underlying medical conditions and, therefore, are considered at high risk for serious complications, ribavarin is a consideration. However, its benefit is also controversial. Remember that bronchiolitis is caused by a virus, and antibiotics will therefore be of no benefit. However, they will be required if the baby develops a bacterial infection on top of the bronchiolitis.

Can I prevent my child from getting bronchiolitis? Preventing healthy infants from getting bronchiolitis by avoiding contact with other people infected with a virus is difficult, if not impossible like the common cold. Remember, most children will be exposed to rsv before their second birthday and the majority of them will sail through with a nasty cold or no illness at all.

There is no immunization currently available to protect against rsv infection. However, infants who have serious underlying medical problems and are at high risk for getting seriously ill from bronchiolitis might gain some protection against rsv infection and bronchiolitis from a monthly injection during the winter season of pooled antibodies to rsv.

Can my child get bronchiolitis more than once? It is possible to get bronchiolitis more than once. That is because the rsv virus changes from season to season and even within the same season. Also, there are different strains of the rsv virus, each of which can cause bronchiolitis. Furthermore, several different viruses can cause bronchiolitis. For example, rsv may cause bronchiolitis the first time and influenza may cause it the second. Thus, bronchiolitis is different from the chicken pox virus, which you typically get only once.

Reprinted from Caring for Kids with permission from Key Porter Books Limited. Copyright © 2006 by The Hospital for Sick Children