HESI American Career College Practice Exam

Vital describes something essential or necessary, especially for life or for a process to continue. In healthcare, it appears in phrases like vital signs—the basic measurements that show whether the body's most important functions are working (pulse, breathing, blood pressure, temperature). The other terms don’t carry that sense of essentialness: volume is about amount or capacity, prognosis is a predicted outcome of a disease, and vertigo is a sensation of spinning or dizziness. So the term that best matches “essential or necessary” is vital.