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Fluids for Maintenance and Replacement

Whether administered either during anesthesia or to a sick patient, fluid therapy often begins with the maintenance rate, which is the amount of fluid estimated to maintain normal patient fluid balance (Table 3). Urine production constitutes the majority of fluid loss in healthy patients.2,3 Maintenance fluid therapy is indicated for patients that are not eating or drinking, but do not have volume depletion, hypotension, or ongoing losses.

TABLE 1

Evaluation and Monitoring Parameters that May Be Used for Patients Receiving Fluid Therapy

  • Pulse rate and quality
  • Capillary refill time
  • Mucous membrane color
  • Respiratory rate and effort
  • Lung sounds
  • Skin turgor
  • Body weight
  • Urine output
  • Mental status
  • Extremity temperature
  • Packed cell volume/total solids
  • Total protein
  • Serum lactate
  • Urine specific gravity
  • Blood urea nitrogen
  • Creatinine
  • Electrolytes
  • BP
  • Venous or arterial blood gases
  • O2 saturation

Replacement fluids (e.g., LRS) are intended to replace lost body fluids and electrolytes. Isotonic polyionic replacement crystalloids such as LRS may be used as either replacement or as maintenance fluids. Using replacement solutions for short-term maintenance fluid therapy typically does not alter electrolyte balance; however, electrolyte imbalances can occur in patients with renal disease or in those receiving long-term administration of replacement solutions for maintenance.

Administering replacement solutions such as LRS for maintenance predisposes the patient to hypernatremia and hypokalemia because these solutions contain more sodium (Na) and less potassium (K) than the patient normally loses.Well-hydrated patients with normal renal function are typically able to excrete excess Na and thus do not develop hypernatremia. Hypokalemia may develop in patients that receive replacement solutions for maintenance fluid therapy if they are either anorexic or have vomiting or diarrhea because the kidneys do not conserve K very well.4

If using a replacement crystalloid solution for maintenance therapy, monitor serum electrolytes periodically (e.g., q 24 hr). Maintenance crystalloid solutions are commercially available. Alternatively, fluid made up of equal volumes of replacement solution and D5W supplemented with K (i.e., potassium chloride [KCl], 13–20 mmol/L, which is equivalent to 13–20 mEq/L) would be ideal for replacing normal ongoing losses because of the lower Na and higher K concentration. Another option for a maintenance fluid solution is to use 0.45% sodium chloride with 13–20 mmol/L KCl added.5 Additional resources regarding fluid therapy and types of fluids are available on the AAHA and AAFP websites.

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