A critical appraisal of intravenous fluids: from the physiological basis to clinical evidence

Fluid management has been a vital part of routine clinical care for more than 180 years. The increasing number of available fluids has generated controversy about the optimal choice of resuscitation fluid. In this review, we provide a critical overview of the different fluids available, their composition, the relevant physiology as well as the published evidence on clinical outcomes to guide their use. Commonly used infusion fluids include semisynthetic colloids and crystalloids; the latter comprises both normal saline (NaCl 0.9%) and the more chloride-restricted 'balanced' crystalloids. Despite their significantly greater intravascular persistence, semisynthetic colloids have an importantly adverse safety profile and are associated with greater incidence of renal failure and increased mortality; their use should be restricted. To date, evidence for clinical benefits associated with albumin solutions is generally lacking; its merits in specific clinical situations are the subject of further investigation. Infusion of normal saline, with its supraphysiological chloride content, is associated with higher serum chloride concentrations and metabolic acidosis, as well as renal vasoconstriction in animal and human models. Infusion of 'balanced' crystalloids is not linked to such changes. Although data on clinical outcomes associated with crystalloid infusion are heterogeneous, advantages of balanced salt solutions might include a lower need of blood products, and lower incidence of renal replacement therapy, hyperkalaemia and postoperative infections. Taken together, a critical appraisal of the data suggests that balanced salt solutions deserve consideration as infusates of first choice.