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The difference between freshwater and saltwater drownings

Q: What is the difference between freshwater and saltwater drownings?

Krishna:

Drowning occurs when the respiratory tract is blocked by any type of fluid. The factors other than hypoxia can cause death. When water enters the trachea, intense spasm of the larynx causes the trachea to close, so that more water cannot enter the lungs. Sometimes, the spasm may not occur, and the large amount of water entering the lungs lead to drowning.

The process of drowning varies significantly between fresh and salt water because of differing osmolarity (solute concentration) compared to blood.

Freshwater Drowning: Freshwater is hypotonic (lower salt concentration) compared to blood. When inhaled, water rapidly passes from the lungs directly into the bloodstream. This massive fluid shift increases blood volume, dilutes electrolytes, and bursts red blood cells (hemolysis), which can cause fatal cardiac arrhythmias within minutes.

Saltwater Drowning: Saltwater is hypertonic (higher salt concentration) compared to blood. Instead of entering the blood, the high salinity draws water out of the circulatory system and into the lungs. This results in severe pulmonary edema (fluid in the lungs) and rapid oxygen deprivation, causing blood to thicken and increasing the risk of cardiac arrest.

Hypertonic salt water—being more concentrated than human blood—creates an osmotic gradient when it enters the lungs. This gradient draws water out of surrounding lung tissues into the alveoli and bronchioles, leading to irritation and inflammation.

Salt water can also cause oxidative stress, dilution of pulmonary surfactant, breakdown of the blood-air barrier, cellular degradation and cell death.

Both environments result in fatal asphyxiation, but their distinct cellular and chemical impacts create different immediate medical emergencies.

90% of drowning cases occur in freshwaters such as rivers and pools. Drowning in fresh water and entering a large amount of pool or river water into the lungs and stomach is much more dangerous than swallowing a lot of sea water. Swallowing plenty of freshwater leads to quick absorption into blood from the gastrointestinal tract due to a lower osmotic pressure than blood; therefore, it increases blood volume in a short amount of time that results in the loss of red blood cells (hemolysis). Unlike freshwater, saltwater does not induce the above complications because of having the equal osmotic pressure to blood, and it just increases slightly sodium and chlorine causing mild symptoms. For this reason, swimmers are advised that if they swallow a lot of water, they try to remove it from the abdomen, and even if they are in a good condition, they should go to the hospital to control the blood electrolytes, as the symptoms may develop within the next few hours. (1)

Salt water aspiration syndrome or saltwater aspiration syndrome is a medical condition caused by the inhalation or aspiration (entry of materials into lungs from mouth) of small amounts of salt water during an underwater dive, leading to lung irritation and inflammation. Unlike drowning or near-drowning, it does not involve ingestion of large volumes of water. It often results from faulty diving equipment or improper breathing techniques, allowing fine water droplets to reach the lower respiratory tract.

The condition begins with a cough, followed by shortness of breath, chest discomfort or pain, shivering, fever and other systemic symptoms. It can resemble a viral infection but improves within hours, especially with supplemental oxygen. While most cases resolve on their own, severe instances may require critical care. Diagnosis is based on clinical history and symptom progression. Salt water aspiration syndrome was first described in 1970.

Footnotes:

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC7036150/

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