The use of intravenous fluid therapy must meet a need that cannot be met by oral administration and is not free from risk. No perfectly physiological intravenous solution is currently available. Intravenous solutions are classified into crystalloids and colloids. For the majority of indications, optimal intravenous fluid therapy is based on the use of crystalloids. The choice of fluid therapy must be personalised based on the patient’s characteristics and prior medical history, the current clinical situation, the osmolality and association of hydroelectrolytic imbalances and the acid-base equilibrium. The use of synthetic colloids is subject to significant restrictions given their negative effects on health outcomes, mainly anaphylactic reactions.