Which solution is isotonic and commonly used for fluid resuscitation?

Which solution is isotonic and commonly used for fluid resuscitation?

• A. Normal saline
• B. Dextrose 5% in water
• C. Half-normal saline
• D. Hypertonic saline

Answer: (A)

Isotonic fluids have an osmolarity similar to blood plasma, so when they’re given intravenously they stay mainly in the intravascular space and expand circulating volume without causing water to move into or out of cells. For fluid resuscitation, you want a rapid increase in extracellular fluid to restore circulating volume, and the solution that fits this need best is normal saline. It’s 0.9% sodium chloride, already isotonic with plasma, so it effectively increases blood volume without shifting water into the cells or drawing water out of them. Dextrose 5% in water acts like a hypotonic fluid after the glucose is metabolized; initially it can raise osmolarity, but as the body uses the dextrose, the remaining fluid becomes hypotonic and can cause water to move into cells, which is not ideal for quick volume expansion and can contribute to hyponatremia if used for resuscitation. Half-normal saline is hypotonic, meaning it can cause cells to swell and is not used for standard resuscitation. Hypertonic saline is reserved for specific, controlled scenarios (such as certain brain injuries or severe hyponatremia) and requires careful monitoring, not routine resuscitation.

Isotonic fluids have an osmolarity similar to blood plasma, so when they’re given intravenously they stay mainly in the intravascular space and expand circulating volume without causing water to move into or out of cells. For fluid resuscitation, you want a rapid increase in extracellular fluid to restore circulating volume, and the solution that fits this need best is normal saline. It’s 0.9% sodium chloride, already isotonic with plasma, so it effectively increases blood volume without shifting water into the cells or drawing water out of them.

Dextrose 5% in water acts like a hypotonic fluid after the glucose is metabolized; initially it can raise osmolarity, but as the body uses the dextrose, the remaining fluid becomes hypotonic and can cause water to move into cells, which is not ideal for quick volume expansion and can contribute to hyponatremia if used for resuscitation. Half-normal saline is hypotonic, meaning it can cause cells to swell and is not used for standard resuscitation. Hypertonic saline is reserved for specific, controlled scenarios (such as certain brain injuries or severe hyponatremia) and requires careful monitoring, not routine resuscitation.