Which of the following is NOT a type of crystalloid solution?

Crystalloids are a category of intravenous fluids that consist of water and electrolytes, which can easily pass through cell membranes. They are primarily classified into three types based on their osmolarity compared to plasma: isotonic, hypertonic, and hypotonic solutions.

Isotonic solutions maintain equilibrium with plasma, hypertonic solutions have a higher osmolarity than plasma, and hypotonic solutions have a lower osmolarity than plasma. Each of these solutions serves specific therapeutic purposes, like hydration, volume expansion, or correcting electrolyte imbalances.

In contrast, colloid solutions consist of larger molecules, such as proteins or starches, that create an oncotic pressure and help to expand blood volume by pulling fluid from tissues into the vascular space. As colloids do not fall under the definition of crystalloids, identifying colloids as the option that is not a type of crystalloid solution is accurate. This distinction is crucial for healthcare providers when selecting the appropriate fluid for a patient's specific needs.