Drowning (cont.)
What happens during drowning?
Drowning occurs when water comes into contact with the
larynx (voice box).
- After an initial gasp, there is an initial voluntary breath holding.
- This is
followed by spasm of the larynx and the development of hypoxemia (hypo=low +
ox=oxygen + emia=blood), or decreased levels of oxygen in the bloodstream.
- Lack
of oxygen causes aerobic metabolism to stop, and the body becomes acidotic. If
not corrected quickly, the lack of oxygen in combination with too much acid may
lead to problems with the electrical conduction system of the heart (cardiac
arrest) and lack of blood supply to the brain.
- As body function declines, the larynx may relax and allow water to enter the
lungs. However, up to 20% of drowning victims have persistent spasm of the
larynx, and no water is aspirated (this was formerly known as
"dry" drowning).
What are the complications of drowning?
- Hypoxemia causing brain damage is the major complication in drowning victims
who do not die.
- Direct lung tissue damage because of water aspirated into the lung can also
occur and lead to pneumonia and
acute respiratory distress syndrome (ARDS).
- If the drowning occurs in colder water risks include hypothermia or a
drop in body temperature. (If the body temperature drops below 95F (35C) get
medical attention immediately.)
- Cervical spine fractures may occur in diving injuries associated with
drowning.
Does the type of drowning matter?
There have been a variety of theories reported regarding the potential
responses of the body to different drowning situations. Most discuss dry vs. wet
drowning and salt vs. fresh water drowning.
Wet vs. Dry Drowning
Most drownings are unwitnessed, and the victim is found floating. While only
a small amount of aspirated water is required to cause significant problems with
lung function, it is the prolonged submersion time and lack of breathing that
causes morbidity due to hypoxemia.
Approximately 10%-20% of drowning victims have dry drowning, but even most
wet drowning victims have less than 4cc/kg of water found in their lungs. For a
50 pound child, this amounts to less than 3 ounces.
Salt vs. Fresh Water Drowning
In the lung, the breathing tubes (trachea, bronchi, bronchioles) branch into
smaller and smaller segments until they end in an air pocket called an alveolus
(plural alveoli). This is the part of the lung where air and red blood cells in
capillary blood vessels come near enough to allow the transfer of oxygen and
carbon dioxide between the two. Alveoli are covered with a chemical called
surfactant that allows the air pocket to open and close easily when breathing
occurs.
When fresh water enters an alveolus, it destroys the surfactant and causes
the alveoli to collapse, unable to open with breathing. A ventilation-perfusion
mismatch occurs in which the body sends blood to parts of the lung that lack
oxygen, resulting in a decrease in the concentration of oxygen in the blood.
Salt water doesn't destroy surfactant, rather it washes it away and damages
the membrane between the alveolus and the capillary blood vessel. One again, the
body sends blood flow to areas of the lung that aren't able to provide it
oxygen, and hypoxemia occurs.
Regardless of the type of water, lung function is compromised, and hypoxemia
occurs. In some circumstances,
electrolyte abnormalities may occur with fresh
water drowning.
Next: What are the risk factors of drowning? »
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