The administration of IV fluid to avoid dehydration, maintain an effective circulatingvolume, and prevent inadequate tissue perfusion should be considered, along with themaintenance of sleep, pain relief, and muscular relaxation, a core element of theperioperative practice of anesthesia. Knowledge of the effects of different fluids hasincreased in recent years, and the choice of fluid type in a variety of clinicalsituations can now be rationally guided by an understanding of the physicochemicaland biological properties of the various crystalloid and colloid solutions available.