Crystalloids, colloids, blood and blood products and substitutes

Intravenous fluids are a core therapy in critical care and perioperative practice. Although most fluids that we use today are very similar to those of the mid 20^th Century, our understanding of the physiology of the cardiovascular system, the microcirculation and the extravascular space has evolved considerably. In modern practice, thought should be given to the distribution of stressed and unstressed blood volume, the glycocalyx and the gelatinous interstitial matrix. All of these components change dynamically in volume depleted states. In the dehydrated patient, if given slowly, most intravenous fluid remains in the circulation. However, if delivered rapidly, much of the it extravasates into the interstitium causing hydraulic damage and oedema. In general, isotonic balanced crystalloid solutions should be used in preference to 0.9% saline for resuscitation, and hypotonic crystalloid solutions, containing generous quantities of potassium, should be used for maintenance. There is minimal indication for colloidal products in modern medicine, with the exception of human albumin solution in liver disease. Blood products are indicated as the primary resuscitation tool in haemorrhagic shock.