PSA - Shallow water drowning, aka shallow water blackout

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Astronuc
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An unexpected result from a seemingly harmless activity - holding one's breath underwater.

https://www.yahoo.com/news/watched-husband-almost-die-front-104525608.html

An otherwise healthy 27-year old man held his breath underwater, then his heart stopped.

It is surprising, since I used to do that in swimming pools, in competition with my brother, or just to see how far I could swim underwater before surfacing. I managed to swim two laps. My brother and I had contests to see who could hold his breath the longest, but we did that sitting in chairs.
 
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berkeman
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I'd like to see what the cardiac rhythm was that he presented during this. It's not obvious why the drowning would lead to cardiac arrest (presumably ventricular fibrillation or ventricular tachcardia, which are the two primary shockable rhythms). This article seems to imply that pre-existing cardiac conditions can lead to cardiac arrest in drowning victims, but the usual problems are hypoxia and fluid in the lungs, not cardiac arrest.

Glad that he survived.

https://www.ncbi.nlm.nih.gov/books/NBK554620/
If no pulse is present, initiate CPR for five cycles (about 2 min), starting with chest compressions, 30 compressions, then two rescue breaths in the cycle. Initiate advanced life support early, which includes advanced airway and use of an automated AED as equipment availability permits. Regurgitation of stomach contents is the most common complication during drowning resuscitation.[2] Active efforts to expel water from the airway with abdominal thrusts or head down positioning should be avoided as they delay ventilation and increase the risk of vomiting and mortality. All water rescue patients who lost consciousness, even if brief, should undergo hospital evaluation. Most patients who require resuscitation efforts will require ICU hospital admission and possibly mechanical ventilation.[2]

Differential Diagnosis​

The unexpected demise of a swimmer can have multiple causes. When evaluating a patient who has lost consciousness in the water, it is crucial to consider all possible causes to intervene effectively. Hypoxic blackout (unconsciousness due to hypoxia) is one of the most common underlying causes of morbidity and mortality in the water. Other differentials to consider are preexistent organic cardiac disease (coronary artery disease or cardiomyopathy), preexistent cardiac arrhythmias, and epilepsy.[2] All of these conditions undergo exacerbation in the oxygen-starved apneic environment of being underwater. Some data has shown that a prolonged QT can also contribute to an increased risk of underwater unconsciousness. Prolonged QT is inducable by medications, metabolic disturbances (hypokalemia), or alcohol.[9] In general, with cardiac-related drowning, the swimmer is usually observed to have stopped swimming on the surface and may demonstrate unusual non-sustained behavior. On the other hand, in a hypoxic blackout, the swimmer may be seen hyperventilating before going underwater, which is followed by failure to surface. Considering these differentials will increase the efficacy of rescue efforts.
 
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