Which intravenous solution is considered isotonic?

The designation of a solution as isotonic refers to its osmolarity being similar to that of the body's own fluids, specifically plasma, highlighting its balanced nature in relation to the extracellular fluid. When intravenous solutions are isotonic, they are capable of being administered safely without causing osmotic shifts that could lead to cell swelling or shrinkage.

Normal saline, which is a solution of 0.9% sodium chloride in water, has an osmolarity of approximately 308 mOsm/L, making it isotonic to blood plasma. It is frequently used for fluid resuscitation and as a diluent for medications.

Lactated Ringer's solution contains a mix of electrolytes (sodium, potassium, calcium, and lactate) in a sterile solution, with an osmolarity close to that of normal plasma. This combination allows it to maintain the balance of fluids and electrolytes effectively in patients, classifying it as isotonic as well.

Dextrose 5% in water (D5W) is initially considered isotonic because it has an osmolarity of approximately 252 mOsm/L when in solution. However, once metabolized, it leaves behind free water, which can lead to a hypotonic effect.