In fluid resuscitation, what does "insensible loss" refer to?

Insensible loss refers to the fluid loss that occurs through the skin and respiration, which is generally not easily measurable or observable. This includes the moisture lost from the skin due to diffusion and crying, as well as the moisture lost during respiration as vapor. These losses are termed "insensible" because they happen continuously and can often go unnoticed, making it challenging to accurately assess or quantify them in clinical practice.

Fluid loss through vomiting, urination, or diarrhea, while significant, is generally considered "sensible loss" because these methods of fluid loss can be seen, quantified, and measured more easily. Therefore, understanding insensible loss is crucial in fluid resuscitation, as it accounts for a portion of total fluid needs that must be replaced to stabilize a patient’s hemodynamics and ensure adequate hydration.