Barotrauma

Introduction

 

Barotrauma is injury caused by differences in pressure across a surface. In ENT we are usually concerned with barotrauma to the ears and that is what this tutorial will discuss. Of course, barotrauma to the sinuses is also possible but it isn't discussed here. Barotrauma is different to decompression injuries. In decompression injuries bubbles of gas appear in tissues when the external pressure falls. It will not be discussed further.

Mechanism

The middle ear is a space inside the bones of the skull. It is surrounded on all sides by bone except for a round aperture closed by the eardrum. It has a single tube linking it to the outside world - the Eustachian tube. It is this tube that ensures that the pressure inside the middle ear is the same as the pressure outside. It works by opening itself repeatedly during the day when we swallow or yawn. When open, the pressure in the nose equalises with that in the ear.

 

The middle ear works best when the pressure on the inside is the same as on the outside. It can amplify better in this situation.

 

Barotrauma of the ears occurs both when the atmospheric pressure (pressure outside the middle ear) is greater than the middle ear pressure and when atmospheric pressure is lower than middle ear pressure. The bone surrounding the middle ear does not change in these situations but the eardrum does. If the outside pressure is high the drum bulges inwards and if the outside pressure is low the drum bulges outwards. 

The images above show the normal situation where air pressure in the middle ear is the same as that outside. This is the optimal situation and the drum may move freely.

The middle image shows a reverse block of the ear where an obstruction lies in the outer ear. The air pressure between the obstruction and the eardrum cannot change easily and changes in atmospheric pressure cause the drum to bulge outwards. This can happen while diving with a wax obstruction.

What makes the Eustachian tube fail?

 

In adults the Eustachian tube is thin and long. It is lined with a respiratory mucosa. Swelling in the mucosa due to infection or inflammation may cause the tube to block off so that it can’t allow air to move through it. Thick mucus or mucosal swelling can also block the Eustachian tube as it enters the ear. Whatever the cause, once the tube is blocked the patient will be susceptible to barotrauma if atmospheric pressure changes.

 

Hence, patients with upper respiratory infections, in whom there may be poor function of the Eustachian tube, are recommended not to fly or dive until they are able to equalize their ears properly. 

 

Children have relatively poorly functioning Eustachian tubes and this makes it harder for them to equalize pressure in the middle ear. This is why we often hear babies crying during the descent of an aircraft. They are developing ear pain due to pressure changes.

Situations that change atmospheric pressure

 

Atmospheric pressure falls when we move up through the atmosphere such as walking up a mountain or going up in a plane. It rises when we go down hills, land in a plane or dive into water and swim below the surface.

 

If the Eustachian tube is working the pressure in the middle ear will change in the same way. So if you go up a hill air pressure on the outside will fall and so will the pressure in the middle ear. This means that the pressures on either side of the eardrum remain equal and the drum can move freely and the hearing will be good. If the Eustachian tube is blocked the pressure in the middle ear won’t change as you go up the hill and the ear drum will bulge outwards into the external canal. The drum won’t work so well and a feeling of deafness will arise. In reality, this situation is less common than one would think because air at a higher pressure in the ear can usually leak out through the Eustachian tube or puff the tube open.

 

The opposite happens when you descend. Imagine that you are in a plane and it has started to descend towards the ground. The pressure outside the ear is low and so is the pressure in the middle ear. The drum is in a good position and you can hear well. As the plane descends the pressure on the outside of the ear starts to rise. If you don’t equalize the pressure by opening the Eustachian tube the drum starts to push inwards. You feel pressure in the ear and then pain and your hearing starts to become dull. Middle ear pressure that is low makes the Eustachian tube problem worse and the tube can 'lock'.

 

If pressure does not equalize the middle ear may fill with fluid leaving the patient with conductive hearing loss for days or weeks.

 

Symptoms and Signs

 

Symptoms

1.      Pressure, fullness or pain in the ear

2.     Reduced hearing

3.     Tinnitus

4.     Dizziness or vertigo

 

Signs

1.      Retraction of the ear drum

2.     Middle ear fluid with or without bubbles of air

3.     Increased blood vessel markings on the drum

4.     Perforation of the drum with clear / blood stained discharge

 

Prevention

 

Not everyone has good Eustachian function. Some have poor function due to acquired disease such as the common cold, nasal allergy or chronic rhinosinusitis. Others are born with the tendency to it.

 

Patients with ear infections are not recommended to fly as this may cause barotrauma. People who cannot equalize their ear pressure (by doing a Valsalva manoeuvre) should avoid scuba diving. Most people will be able to help their problem by pinching and blowing their nose during descent or by sucking a sweet and swallowing.

 

Treatment

 

In general, all that is required is simple pain relief and time. Treating any underlying chronic conditions such as chronic rhinosinusitis is sensible and may prevent problems in the future.

 

If the ear fills with an effusion and this persists for more than three months, a grommet insertion will help with hearing and the pressure sensation in the ear. It may help any tinnitus that is present, too.

 

Perforations caused by barotrauma generally heal without any intervention.