Crystalloids have which relevancy window?

• A. 1 hour relevancy
• B. 48 hour relevancy
• C. 24 hour relevancy
• D. 72 hour relevancy

Answer: (A)

Crystalloids act quickly but are redistributed out of the intravascular space rapidly. After a crystalloid bolus, the effect on circulating volume is most evident in the first hour because most of the fluid moves into the interstitial space within that time. That’s why the relevant window for assessing their immediate impact is about one hour—the intravascular volume expansion they provide is short-lived. Longer windows like 24, 48, or 72 hours would overstate how long crystalloids stay effective in maintaining intravascular volume.