Question

A patient is in the emergency room and severely dehydrated. The physician ordered fluids for him. Given the fact that our blood is made of cells and plasma (fluid), we would expect that it has an overall tonicity of X micrograms/pint. What corresponding tonicity should the fluids the hospital gives him be in order to help or rehydrate the patient?

Answer 1

IV fluids given to the patient for rehydration should correspond to the tonicity of blood plasma. Intravenous fluids maintain fluid and electrolyte balance, replace extracellular fluid volume losses, correct existing electrolyte or acid-base disorders and provide a source of glucose.

Blood plasma has an osmolality of 288 mOsm/kg. Hence, the IV solutions given to the patient should be in the range of tonicity of blood plasma as given above. The soultions that are isotonic to blood plasma and commonly used as intravenous injections for rehydration are 0.9% NaCl solution (normal saline), it has an osmolality of 308 mOsm/kg. Another solution that can be used as an IV fluid to make up the loss of body fluid and electrolytes is Sterofundin with an osmolality of 309 mOsm/kg.