Maintenance Intravenous Fluids in Acutely Ill Patients.

A critical aspect of the care of acutely ill patients is the administration of intravenous fluids. Intravenous fluids may be required as a bolus infusion for resuscitation or as a continuous infusion when sufficient fluids cannot be ingested orally. The goal of maintenance intravenous fluids is to preserve the extracellular volume while maintaining a normal electrolyte balance. An appropriate maintenance fluid provides an adequate quantity of both water and electrolytes to ensure good tissue perfusion without causing complications related to fluid overload or volume depletion. It also prevents the development of hyponatremia, hypernatremia, and other electrolyte imbalances. Despite the almost ubiquitous need for intravenous fluids in acutely ill patients, there has been little consensus on the most appropriate rate of administration and composition of intravenous fluids, and practice patterns with respect to maintenance fluids vary widely.1-3 In addition, acutely ill patients frequently have conditions that impair normal water and electrolyte homeostasis (Table 1), and choosing the appropriate volume and composition of intravenous fluids requires great care.4 Intravenous fluids can be classified, according to the concentration of sodium plus potassium in the fluid, as being either isotonic (approximately equal to the plasma sodium concentration) or hypotonic (less than the plasma sodium concentration). The dextrose content of intravenous fluids has no effect on the tonicity, since the dextrose is rapidly metabolized when it enters the bloodstream and should not produce hyperglycemia. A prevailing practice has been to administer hypotonic maintenance intravenous fluids in both children and adults.1,5,6 This practice has been associated with a high incidence of hospital-acquired hyponatremia and more than 100 reports of iatrogenic deaths or permanent neurologic impairment related to hyponatremic encephalopathy,7-11 since acutely ill patients may have disease states associated with an excess of arginine vasopressin (AVP) (Fig. 1). This excess impairs excretion of free water and may aggravate hyponatremia.15,16 Over the past decade, many studies have evaluated the association between the composition and quantity of maintenance fluids and the development of hyponatremia. Recent data also suggest that rapid volume expansion with 0.9% saline (normal saline), as compared with balanced electrolyte solutions, may result in untoward complications.17 The current review considers the physiological principles that guide the appropriate selection of intravenous fluids, as well as the recent literature evaluating the safety of various intravenous fluids with respect to their composition and rate of administration. From the Department of Pediatrics and Division of Nephrology, Children’s Hospital of Pittsburgh of the University of Pittsburgh Medical Center (UPMC), University of Pittsburgh School of Medicine, Pittsburgh (M.L.M.); Renal Consultants of Houston, Houston (J.C.A.); and the Division of Nephrology, Hospital Italiano de Buenos Aires, Buenos Aires ( J.C.A.). Address reprint requests to Dr. Moritz at the Division of Nephrology, Children’s Hospital of Pittsburgh of UPMC, 1 Children’s Hospital Dr., 4401 Penn Ave., Pittsburgh, PA 15224, or at moritzml@ upmc . edu.