Hypotonic IV Solutions
Hypotonic solutions have an osmolality (how concentrated a solution is) of less than 240 mOsm/liter. They are less concentrated than blood. They exert less osmotic pressure than the fluid in the extracellular compartment which allows water to be drawn from the extracellular fluid. Blood cells will draw these solutions into them causing the blood cells to swell and burst. There is only one hypotonic solution in common use and that is 0.45% sodium chloride (1/2 Normal Saline). It has an osmolality of 155, a pH of 5.6, and contains 77 mEq of sodium and 77 mEq of chloride. Continuous infusion can cause dilution and depletion of electrolytes because of the small amount of sodium in this particular mixture resulting in hyponatremia. Because there are no calories in the solution, the patient is going to become calorie depleted as well if it is infused for a long period.
There is only one hypotonic solution: 0.45% sodium chloride.
Isotonic IV Solutions
Isotonic solutions have the same tonicity as plasma so that when they are infused into a vein, water neither enters or leaves the cells. They have the same concentration as blood. These kinds of IV solutions are used to expand the extracellular fluid volume and do not cause any fluid to move from into or out of the blood cells. Isotonic solutions have an osmolality of 240 to 340 mOsm/liter.
Isotonic solutions include 0.9% Sodium Chloride, Dextrose 5% in Water, Dextrose 5% and 2.5% saline, Dextrose 5% in water and 0.45% saline, Lactated Ringer’s, Dextrose 2.5% in 1/5 strength Lactated Ringers, 6% Dextran and and 0.9% saline, 10% Dextran and 0.9% saline and a number of formulated electrolyte solutions (i.e., Normosol R, Isolyte E, Plasmalyte R).
Hypertonic IV Solutions
A hypertonic solution is one that has an osmolality greater than 340 mOsm/kg. They are more concentrated than blood. Hypertonic solutions exert more osmotic pressure than the extracellular fluid so when these solutions are infused, fluid gets pulled into the vascular system. You want to monitor patients receiving any hypertonic solutions for fluid overload, particularly if they are being given at a rapid rate of infusion.
There are many hypertonic IV solutions. Most common ones you will see used are 5% Dextrose in 0.45 Sodium Chloride, 5% Dextrose in 0.9% Sodium Chloride, 5% Dextrose in Lactated Ringer’s Injection, Dextrose 10% in Water and 3% Sodium Chloride.
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