Veterinarians use fluid replacement frequently to treat dogs that suffer electrolyte loss through diarrhea and vomiting. They create an "isotonic" solution that will mimic the ion levels found in the blood stream (285 mOsmol/kg of water) and essentially rebalance the system by imbuing the plasma with any lost ions. Rehydrate can be used therapeutically at a two-tablet dose to provide the best hydration for animals that have pronounced fluid losses.
Osmolality is the concentration of a solution. In other words, it is a measurement of the amount of a solute (electrolytes, anti-oxidants, or minerals) that dissolves in a solvent (like water) compared to the amount of solvent in a solution. In the blood stream this refers to the proteins, ions, and anything else dissolved in the plasma. The normal range of canine plasma is between 280-300 mOsmol/kg of water. Rehydrate is designed so that one tablet dissolved into 16 ounces of water provides a 145 mOsmol/kg of water (290 mOsmol/kg of water for a therapeutic two tablet dose in 16 ounces of water) compared to 6 mOsmol/kg for plain tap water. This causes a dilution of the plasma in the blood stream. If plasma osmolality decreases, water must enter cells and the cellular volume increases. Therefore, drinking tap water may cause cellular water retention and bloating where as Rehydrate will reduce the cellular volume increase and supply much needed ions to the blood stream.
HOW IS OSMOLALITY MEASURED?
Osmolality is expressed in units of measurement known as osmoles or milliosmoles (one thousandth of an osmole), per 1000 grams (a very small unit of weight) of solvent. An osmole is the weight of the molecules (the smallest naturally occurring particles of a substance) that make up a solute, divided by the number of particles or ions (electrically charged particles) that they separate in a solution. The molecules that make up the solute are usually measured in grams.
WHAT DOES THIS HAVE TO DO WITH THE ACTIVE DOG?
EVERYTHING! - Like we said earlier, osmolality is a term used to describe the concentration of particles dissolved in a solution. Therefore, the more "stuff" a rehydration beverage contains, the higher its osmolality will be. Optimal absorption of fluids within the body happens when solutions are equal in terms of osmolality and what naturally occurs in the body. As mentioned before, the osmolality of the blood ideally is between 280-300 mOsmol/kg, and fluctuates depending on the status of the animal. So, as the osmolality of your sports drink increases above 300 mOsmol/kg, efficient uptake from the GI tract is decreased. In fact, solutions with high osmolalities can actually draw fluid out of the body. Osmolality determines if your sports drink will give you the results you are looking for!