Maintenance Fluid Therapy

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Multiple physiologic processes work in concert to maintain appropriate fluid and electrolyte balance. In health, interactions between the kidney, hormonal secretion, and neuronal signals preserve effective circulating volume and osmolar homeostasis. An important participant in this carefully calibrated scenario is the individual’s perception of thirst and ability to consume water. In certain clinical situations, a child may not be able to take in the appropriate amount of water necessary to keep up with ongoing losses. Nausea, emesis, sedation, mechanical ventilation, and numerous other conditions encountered with a hospitalized child may limit enteral intake of fluids and jeopardize the ability to preserve physiologic balance. In these settings, one may provide intravenous fluids to deliver the daily requirement of water and electrolyte. Such fluids, designed to maintain homeostatic balance and compensate for normal daily losses, are often referred to as maintenance intravenous fluids. Maintenance fluids replace the usual insensible losses and anticipated urinary output when a child cannot do so on their own by autoregulation, kidney function, thirst, and oral intake. Maintenance fluids are designed to prevent dehydration or volume depletion from occurring. They are not designed to correct fluid depleted states or to compensate for abnormal shifts of fluids between body compartments, nor are they intended to expand vascular volume prophylactically. In addition to providing the daily requirement of water, maintenance prescriptions usually also provide a daily amount of sodium, chloride, and potassium, the basic electrolytes lost in normal urinary excretion. Systems to determine maintenance prescriptions rely on a series of assumptions, including normal volume status, normal renal function and urinary output, normal insensible losses, and a lack of additional ongoing losses. Situations where these assumptions do not hold will require review and adjustment to the maintenance fluid prescription. Recently there has been controversy about the appropriate method for prescribing maintenance fluids, noting the potential for complications and calling into question