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Osmolarity vs. Osmolality

I am confused about the difference between osmolarity and osmolality.  Is it an equal comparision to compare the osmolarity of the IV solution to the osmolality of the blood plasma  when trying to determine if a peripheral or central venous access device should be used? If not, how do we compare these?

Thank you

I just finished reviewing a

I just finished reviewing a chapter in a book I am writing that had this very piece of information. Both terms measure the concentration of solutes and both are interchangable. Osmolarity measure the volume of fluid and dissolved particles, is expressed as mOsm/L, most often used to measure fluids outside the body, eg in the bag. Osmolality measure the weight of fluids, expressed as mOsm/kg, most often used to measure fluid inside the body. 1 liter of water weighs 1 kilogram so those terms are used interchangably. . 

Lynn Hadaway, M.Ed., RN, NPD-BC, CRNI

Lynn Hadaway Associates, Inc.

PO Box 10

Milner, GA 30257


Office Phone 770-358-7861

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