Colloids: Details and Myths

Colloids function as essential tools in intensive care by exerting osmotic pressure to maintain intravascular volume, yet common misconceptions persist regarding their definition and clinical application. While albumin serves as a primary colloid by remaining in solution to pull water into the circulatory system, whole blood acts as a suspension rather than a colloid because hemoglobin is sequestered within red blood cell membranes. Understanding this distinction is critical for fluid management, as 5% albumin provides volume expansion without significant osmotic pull, whereas 25% albumin exerts a hyper-oncotic effect. Clinical decisions regarding fluid resuscitation rely on balancing hydrostatic pressure against colloid-oncotic pressure, governed by Starling’s forces. Recognizing that blood is not a colloid and that albumin concentrations dictate specific physiological outcomes allows for more precise, evidence-based fluid administration in critically ill patients.