The Euvolemic Patient

The Euvolemic Patient is a topic covered in the Washington Manual of Medical Therapeutics.

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  • In a euvolemic patient, the goal of fluid and electrolyte administration is to maintain homeostasis. The best way to accomplish this is to allow free access to food and oral fluids. Patients who are unable to tolerate oral intake require maintenance fluids to replace renal, gastrointestinal (GI), and insensible fluid losses.
  • The decision to provide maintenance IV fluid (IVF) should be thoughtfully considered and not administered by rote. Fluid administration should be reassessed at least daily. Patient weight, which may indicate net fluid balance, should be monitored carefully.
  • Consider the water and electrolyte needs of the patient separately when prescribing IVF therapy.
    • Minimum water requirements for daily fluid balance can be approximated from the sum of the required urine output, stool water loss, and insensible losses.
      • The minimum urine output necessary to excrete the daily solute load is the amount of solute consumed each day (roughly 600–800 mOsm/d in an average individual) divided by the maximum amount of solute that can be excreted per liter of urine (maximum urine concentrating capacity is 1200 mOsm/L in healthy kidneys). The result is an obligate urine output of at least 0.5 L/d.
      • The water lost in stools is typically 200 mL/d.
      • Insensible water losses from the skin and respiratory tract amount to roughly 400–500 mL/d. The volume of water produced from endogenous metabolism (<250–350 mL/d) should be considered as well. The degree of insensible loss may vary tremendously depending on respiratory rate, metabolic state, and temperature (water losses increase by 100–150 mL/d for each degree of body temperature over 37°C).
      • Fluid from drain losses must be factored in as well.
      • After adding each of these components, the minimum amount of water needed to maintain homeostasis is roughly 1400 mL/d or 60 mL/h.
    • Electrolytes that are usually administered during maintenance fluid therapy are Na+ and K+ salts. Requirements depend on minimum obligatory and ongoing losses.
      • It is customary to provide 75–175 mEq Na+/d as NaCl. (A typical 2-g Na+ diet provides 86 mEq Na+/d.)
      • Generally, 20–60 mEq K+/d is included if renal function is normal.
      • Carbohydrate in the form of dextrose, 100–150 g/d, is given to minimize protein catabolism and prevent starvation ketoacidosis.
    • Table 12-1 provides a list of common IV solutions and their contents. By combining the necessary components, one can derive an appropriate maintenance fluid regimen tailored for each patient.
      Table 12-1: Commonly Used Parenteral Solutions
      IV SolutionOsmolality (mOsm/L)[Glucose] (g/L)[Na+] (mEq/L)[Cl] (mEq/L)Descriptive text is not available for this image Equivalents (mEq/L)
      0.45% NaCla154b77770
      0.9% NaCla308b1541540
      3% NaCl10265135130
      Lactated Ringer’sc274b13010928

      aNaCl 0.45% and 0.9% are half-normal and normal saline, respectively.

      bAlso available with 5% dextrose.

      cAlso contains 4 mEq/L K+, 1.5 mEq/L Ca2+, and 28 mEq/L lactate.

      D5W, 5% dextrose in water.

    • Example: A patient is admitted for a procedure and is made nothing by mouth. To maintain homeostasis, you must replace 2 L of water, 154 mEq Na+, 40 mEq K+, and 100 g dextrose over the next 24 hours (values are within water and electrolyte requirements described earlier).
      • 2 L of water: Dose fluid at 85 mL/h (2000 mL ÷ 24 hours)
      • 154 mEq of Na+: Use 0.45% normal saline (NS) (77 mEq Na+/L)
      • 40 mEq of K+: Add 20 mEq/L KCl to each liter of IVF
      • 100 g dextrose: Use D5 (50 g of dextrose/L)
      • Order: D5 0.45% NaCl with 20 mEq/L KCl at 85 mL/h

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