Salt in the pool: off topic
I was visiting friends when we looked up from the breakfast table and saw the dog lying motionless in the swimming pool.  The women were faster afoot and had him out of the pool lying on the deck by the time I got there.  It was unconscious and its breathing and heartbeat, although audible, were depressed.  Mostly it seemed to be suffering from hypothermia.  My principle concern was to drain any water from the airway.  This we did by holding him upside down.  Over the next hour or so he began to come around.  His heart and breathing picked up, had started to shiver and was able to stand a bit. 

I tried to explain why fresh water in the lungs is so dangerous.  Saltwater in the lungs is bad enough.  I have seen x rays of humans that had been near drowning in salt water.  The lungs look very abnormal.  But an x-ray of the lungs of a near drowning victim in fresh water looks just about normal.  The difference is that when salt water enters the lungs it sucks water into itself from the blood by osmotic pressure.  The red blood cells shrivel but do not break.  But with fresh water the movement is in the other direction.  The water goes into the capillary blood, diluting the plasma salt so that the red blood cells swell and then break, releasing their potassium.

Potassium changes the way the cell membranes react to electric charge.  If there is too much potassium outside a cell no electrical signal can pass, which means muscles cannot contract.  That stops the heart and lungs, which is bad enough.  But it’s actually worse.  Effective circulation of the blood depends on having an adequate pressure and also depends on having vascular tone. 

Like a city’s water system the circulation goes through a branching system of conduits, and the flow is regulated by the pressure of tiny smooth muscle cells squeezing tiny peripheral vessels as the flow of water in the mains is regulated by opening and closing taps.  If more flow is needed such as where muscles are working or a region of the brain is working the local vessels relax, and flow increases.  If all the taps were opened the pressure in the mains would fall and much of the city would be without water.  If the vascular tone in the body collapses the heart is unable to continue keeping a viable blood pressure and the blood pools in the veins where it is unable to be pumped out by the heart. 

In time you could restore the water in the city by asking everybody in town to turn off their taps and be a bit more reasonable in their demands.  But If potassium has caused all the vessels to relax they cannot contract until the potassium is swept away by more blood flow, and there isn’t any.  The pooch had pretty well shut down with only a greatly reduced cardiac output and almost no respiration, but the vascular tone was still there and recovery was possible.  There cannot have been more than a tiny amount of water that got to the lungs.  We were all lucky.

I have long wondered whether pools would be safer if people put enough salt in them so that there would be the same osmotic potential as blood.  That would give a few moments more during which a life could be saved, at least I think it would.  It’s no use expecting pool maintenance people to advertise, “We give you a drowning proof pool.”  Lives saved would be few compared with lives lost and the liability would be extreme.  No government is likely to require it since there is to the best of my knowledge no proof it would make a difference.

But I think somebody who wanted to make the world a tiny bit better might stir up interest and get the issue studied.  It would never have the impact of things that are now routine like supervision, safe water, properly designed pools, restricted access to pools and so forth.  But there is a project for you if you are so inclined. 

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