What defines crystalloids in IV fluid therapy?

Crystalloids in IV fluid therapy are defined by their ability to cross cell membranes. These intravenous solutions contain electrolytes and other small molecules that can easily diffuse across biological membranes, allowing them to effectively hydrate cells and maintain or restore fluid balance in the body. This characteristic sets crystalloids apart from colloids, which are composed of larger molecules and do not readily pass through cell membranes.

This property of crossing cell membranes is crucial in clinical settings, as crystalloids can be used to manage hydration levels, electrolytes, and overall fluid status in various medical situations, from rehydration in patients to maintaining blood pressure. As crystalloids can move between intravascular and interstitial spaces, they can be rapidly distributed throughout the body, making them a common choice for fluid replacement therapies.