Drowning (cont.)

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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 mismatch can develop where blood is pumped to parts of lung where no oxygen is available to be absorbed. This may lead to a decrease in the concentration of oxygen in the blood called a ventilation-perfusion mismatch.

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 because of the lack of surfactant, and the effect it has on lung function. In some circumstances, electrolyte abnormalities may occur with fresh water drowning.

What are the risk factors of drowning?

There are two peak ages for drowning: children aged younger than 4 and young adults aged 15 to 25.

  • Infants less than one year old most often drown in bathtubs.
  • Children younger than age 5 most commonly drown in residential swimming pools.
  • Young adults tend to drown in larger bodies of water (for example, rivers and lakes). Neck fractures caused by diving into shallow water are associated with drowning in this age group. Alcohol is also implicated in up to 50% of drownings in this age group.
  • Medical emergencies that occur in the water also can lead to drowning. These may include, among others, seizures, heart attack (myocardial infarction), sudden cardiac death, and hypoglycemia (low blood sugar in a person with diabetes).
Medically Reviewed by a Doctor on 7/3/2014

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