Barotrauma

Barotrauma is tissue injury caused by a change in pressure, which compresses or expands gas contained in various body structures.

Increased pressure outside the body is transmitted equally throughout the blood and body tissues, which do not compress because they are composed mainly of liquid. Thus, a person's leg, for example, does not feel squeezed as water pressure increases. However, gases (such as the air inside the lungs, sinuses, or middle ear or inside a face mask or goggles) compress or expand as outside pressure increases or decreases. This compression and expansion can cause pain and damage to tissue.

Nonpulmonary Barotrauma

Nonpulmonary barotrauma is injury to gas-filled parts of the body other than the lungs caused by increasing pressure that occurs during descent.

At 2 atmospheres absolute pressure (a depth of about 33 feet), air in gas-filled structures of the body is compressed to one half its original volume. If the pressure inside these structures is not equalized with surrounding water pressure, the pressure difference can strain and damage the surrounding tissue.

Symptoms

Divers often use the term "squeeze" for injuries caused by differences in pressure. If a diver does not properly equalize pressure in the face mask, the relatively lower pressure inside the mask causes it to act like a suction cup applied to the eyes. The difference in pressure inside and outside the mask causes blood vessels near the surface of the eyes to dilate, leak fluid, and finally burst and bleed. Although the eyes appear red and bloodshot, vision is not affected.

If pressure in the middle ear becomes lower than the water pressure, the resulting stress causes a painful inward bulge of the eardrum (see Section 19, Chapter 220). When the pressure becomes high enough, the eardrum ruptures, resulting in a rush of cold water into the middle ear, causing vertigo (severe dizziness with a spinning sensation), disorientation, nausea, and sometimes vomiting. These symptoms may place the diver at risk of drowning. The vertigo diminishes as the water in the ear reaches body temperature. A ruptured eardrum impairs hearing and may lead to a middle ear infection, causing pain and producing discharge from the ear. The inner ear can be injured as well, causing a sudden loss of hearing, buzzing in the ear (tinnitus), and vertigo.

Pressure differences have similar effects on the sinuses (air-filled pockets in the bones around the nose), causing facial pain or headaches, and on the air-filled pockets in or under a tooth or filling, causing toothache.

People who dive while holding their breath may feel a sensation of their chest being squeezed when descending. This sensation is not experienced by those who breathe compressed air while diving.

Prevention and Treatment

Pressure in the lungs and airways is automatically equalized with outside pressure when a supply of pressurized air is available at depth, as from a diving helmet or air tank. This pressurized air also equalizes pressure in the sinuses, as long as the openings to the sinuses are not narrowed by inflammation due to allergies or an upper respiratory tract infection. Pressure in a face mask is equalized by blowing out air from the nose into the mask. Divers equalize pressure differences in the middle ear by yawning or swallowing, which opens the tube connecting the middle ear and the back of the throat (eustachian tube).

Wearing earplugs or a tight-fitting wet suit hood creates a closed space between the earplug and the eardrum in which pressure cannot be equalized. The pressure inside goggles cannot be equalized either. Therefore, neither earplugs nor goggles should be worn during diving.

When nasal congestion prevents pressure in the ears and sinuses from being equalized, decongestants (such as pseudoephedrine taken by mouth before diving) may temporarily unclog blocked nasal passages, eustachian tubes, or sinuses.

A ruptured eardrum usually heals by itself, although a middle ear infection requires antibiotics given by mouth or as eardrops. A rupture between the middle and inner ear may require prompt surgical repair to prevent permanent damage.

Pulmonary Barotrauma

Pulmonary barotrauma is injury caused by the expansion of air held in the lungs due to decreasing pressure during ascent.

Because air under high pressure is compressed, each breath taken at depth contains many more molecules than a breath taken at the surface. At 33 feet (2 atmospheres absolute), for example, each breath contains twice as many molecules as a breath taken at the surface (and therefore depletes an air tank twice as rapidly). As pressure decreases, air expands--its volume increases. So if a diver fills his lungs with compressed air at 33 feet and ascends without freely exhaling, the volume of air doubles, causing the lungs to overinflate.

Overinflation of the lungs can rupture small air sacs, allowing air to leak out. Air bubbles can enter the blood (air embolism (see Section 4, Chapter 46)) and travel to any organ in the body and block small blood vessels, most commonly those of the brain and heart. At best, air embolism places the diver at risk of drowning. At worst, the diver may die within minutes. Air embolism is a leading cause of death among divers.

Air that leaks out of the lungs can be trapped in the space between the lungs and the chest wall, causing the lung to collapse (pneumothorax (see Section 4, Chapter 52)). Alternatively, air may be forced out of the lungs into the tissues surrounding the heart (pneumomediastinum) and under the skin of the neck and upper chest (subcutaneous emphysema).

The most common cause of pulmonary barotrauma is breath-holding during an ascent from a scuba dive, typically resulting from running out of air at depth. In panic, a diver may forget to exhale freely as air in the lungs expands during the ascent. Air embolism can occur in as little as 4 feet of water if a person breathing pressurized air holds his breath while ascending.

Symptoms

Symptoms of air embolism usually appear within 1 to 2 minutes of reaching the surface. Air embolism to the brain often resembles a stroke, resulting in headache, confusion, agitation, and partial paralysis. Some people have sudden loss of consciousness or seizures. Severe air embolism can block blood flow through the heart and the large arteries, leading to shock (see Section 3, Chapter 24) and death.

Pneumothorax and pneumomediastinum cause chest pain and shortness of breath. Some people cough up blood or develop bloody froth at the mouth. Air in the tissues of the neck can impair the vocal cords, causing the voice to sound different. Subcutaneous emphysema produces a crackling sensation when the affected area of skin is touched.

Prevention and Treatment

To prevent pulmonary barotrauma, divers using an air supply, such as a scuba tank, must not hold their breath during ascent. Any air inhaled at depth--even the depth of a swimming pool--must be exhaled freely during ascent.

A diver who loses consciousness during ascent or very shortly afterward is assumed to have air embolism and must be treated promptly. A person who has air embolism is given oxygen immediately and must be returned at once to a high-pressure environment, so that the air bubbles are compressed and forced to dissolve in the blood. A number of medical centers have high-pressure (recompression or hyperbaric) chambers for this purpose. Flying, even at a low altitude, reduces atmospheric pressure and allows bubbles to expand further, but it can be justified if it saves substantial time in getting the person to a suitable chamber. If possible, the person should fly in a plane pressurized to sea level, or the plane should not fly above 1,000 feet.

A small pneumothorax does not require treatment, but a large pneumothorax causes severe breathing problems and requires insertion of a plastic tube into the chest to remove the air. Treatment of pneumomediastinum and subcutaneous emphysema usually is bed rest and oxygen given through a face mask.