Question

Question: Now that you know the difference between Hypotonic and hypertonic solutions, explain which of the following scenarios is more dangerous: Drowning in a swimming pool -or bath tubs- or drowning in the saltwater like sea or ocean?

Answer 1

The cell is surrounded by a membrane that separates the contents of the cell and regulates the exchange with the environment. The cell membrane works as a very selective filter that regulate the entry and exit of substances. Water can freely cross the membrane by simple diffusion: this shift is called osmosis. Instead the mineral salts and many other substances do not normally cross the cell membrane. The movement of water through the sides of the membrane depends on the concentration of salt (for example sodium chloride) on both sides of the membrane itself. The isotonic solution has the same salt concentration present inside red blood cell so the flow of incoming water in the red blood cell is equal to the leaving water and the cellular volume does not change. The water will spread from low solute concentration compartment to the high solute concentration compartment. Regarding blood, which has a concentration of 0,9% of NaCl, solutions with lower salt content are called hypotonic, instead the solutions with higher concentration are called hypertonic. Of course freshwaters (lakes, rivers, swimming pools) is hypotonic than blood, instead of seawater, which has an average content of NaCl 3,5%, is strongly hypertonic. The different salt concentration between freshwater and seawater cause several effects in relation to drowning in one or the other. The freshwater, especially chlorinated swimming pools, seriously damages the alveoli with consequential disruption, thus decreasing the possibility to oxygenate the blood (even after rescue).

Drowning in fresh water

The drowning in fresh water leads to the rapid passage of large quantities of water from the lungs to the blood (even more than 50% of the water sucked in after a few minutes). This is due to the fact that fresh water is hypotonic compared to the blood and then passes into the bloodstream by osmosis. This passage through the alveolar-capillary membrane occurs quickly and leads dilution of the blood (hemodilution), hyponatremia, and an increase of its total volume (hypervolemia). The diluted blood becomes hypotonic compared to the cells and leads the diffusion of water in the cells, mainly red blood cells, causing hemolysis, hyperkaliemia and, in more serious cases, hemoglobinuria with acute renal glomerular damage. Hemolysis is usually so important that the oxygen carrying capacity is strongly impaired (severehypoxia). The decreased concentration of salt (mostly sodium chloride and calcium) and plasma proteins, together with reduced availability of oxygen to the fact of hemolysis, may be responsible for severe anoxic brain damage and atrial fibrillation leading immediately to death.

Drowning in Sea water

Drowning in sea waters determines various physiological phenomena depending on the fact that sea water is hypertonic compared with blood. The pulmonary flooding leads to the rapid transition of large quantities of water by osmosis from the vascular district to the lung parenchyma (diffuse pulmonary edema). At the same time a certain amount of salt moving from the lung to the blood is the cause of tissue damage. The removal of water and the gain of salts with a rapid increase in the concentration of salts themeselves cause hypernatriemia and hyperchloremia with consequential plasmolysis (wrinkling of red blood cells). Plasma volume decreases (hypovolemia) and blood pressure drops rapidly and severe hypoxia occurs. At first there is tachycardia, which is followed by a pronounced bradycardia (until cardiac arrest) and then damages caused by cerebral anoxia begin to appear.

  Two different mechanisms of absorption of water drawn is used in two types of drowning, death occurs in a few minutes: 2 to 6, when it comes to fresh water, 6 to 8 in the case of sea water.The fatal drowning in fresh water is therefore faster than in salt water as it is evident that the attempt to bring out fresh water from the lungs is useless, because this, being hypotonic, quickly enters into the circulation. Whereas the sea water is hypertonic and recalls plasma into the lungs, so it should droped drainage: for this purpose can be useful Trendelenburg position. Therefore even if time difference is relatively small it indicates that drowning in the sea have more chances of be saved provided that the assistance is prompt. Therefore drowning in a swimming pool which is an example of fresh water is more dangerous than drowning in sea water, an example of hypertonic solutions.