Ringer's lactate is best described as which type of crystalloid for resuscitation?

• A. Isotonic crystalloid
• B. Hypertonic crystalloid
• C. Hypotonic crystalloid
• D. Colloid solution

Answer: (A)

Ringer's lactate is best described as an isotonic crystalloid. Crystalloids are solutions with small solutes that freely distribute across capillary membranes, and isotonic means their osmolality is close to that of plasma. When used for resuscitation, isotonic crystalloids expand the extracellular fluid, including the intravascular space, without causing large shifts of water into or out of cells. Ringer's lactate contains electrolytes similar to plasma (sodium, chloride, potassium, calcium) plus lactate as a buffering agent, and its osmolarity matches plasma closely, making it suitable for volume replacement. It is not hypertonic, which would draw water out of cells, nor hypotonic, which could cause cellular swelling, and it is not a colloid, which uses large molecules to stay mainly within the vascular space.