Isotonic IV solutions have osmolality close to plasma. Which option best reflects this, including two typical examples?

• A. Solutions with osmolality close to plasma (approximately 250-375 mOsm/L). Examples: 0.9% normal saline and lactated Ringer's.
• B. Solutions with osmolality higher than plasma.
• C. Solutions with osmolality far lower than plasma.
• D. Solutions with osmolality not linked to plasma.

Answer: (A)

Isotonic IV solutions have osmolality close to blood plasma, so they stay mainly in the intravascular space and expand circulating volume without causing water to move into or out of cells. This typically places their osmolality in a range similar to plasma, and two common examples are 0.9% normal saline and lactated Ringer's solution. Because their osmolality matches plasma, these fluids increase extracellular/intravascular volume without creating shifts of water across cell membranes. In contrast, solutions with higher osmolality than plasma are hypertonic and tend to pull water out of cells into the bloodstream, while solutions with lower osmolality than plasma are hypotonic and can cause water to move into cells, potentially leading to cellular swelling.