Which IV fluid is isotonic and commonly used for fluid resuscitation?

• A. Ringer's lactate
• B. Normal saline (0.9% NaCl)
• C. D5W
• D. Half normal saline (0.45% NaCl)

Answer: (B)

Normal saline (0.9% NaCl) is classified as an isotonic intravenous fluid, meaning it has a similar osmolarity to that of the body's plasma. This characteristic makes it particularly effective for fluid resuscitation because it helps to restore and maintain vascular volume without significant movement of fluid into or out of the cells. When used in resuscitation, isotonic fluids like normal saline can effectively increase intravascular volume, improving perfusion and oxygen delivery to tissues.

In contrast, Ringer's lactate, while also isotonic, contains multiple electrolytes that may be more appropriate in specific clinical scenarios, such as trauma or burns. D5W, or 5% dextrose in water, is actually hypotonic once metabolized because the dextrose is quickly utilized by the body, leading to a dilution of remaining fluid and potentially causing fluid shifts. Half normal saline is hypotonic as well, which can also lead to fluid shifts that are not ideal during resuscitation efforts. Therefore, normal saline stands out as the go-to isotonic fluid for immediate volume resuscitation.