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Example: 70-kg man (1 L = 1 kg)
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- Intracellular: 28,000 mL (40% of BW)
- Extracellular: 14,000 mL (20% of BW)
- Plasma: 3500 mL (5% of BW)
- Interstitial: 10,500 mL (15% of BW in a 70-kg man)
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Total blood volume = 5600 mL (8% of BW in a
70-kg man)
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• Man, 20–36 mL/kg (1.15–1.21
L/m2) • Woman, 19–31 mL/kg
(0.95–1.0 L/m2)
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The minimum obligate water requirement to maintain homeostasis
(if temperature and renal-concentrating ability are normal and solute [urea,
salt] excretion is minimal) is about 800 mL/d, which
would yield 500 mL of urine.
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2500 mL/d (about 35 mL/kg/d baseline)
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- Oral liquids: 1500 mL
- Oral solids: 700 mL
- Metabolic (endogenous): 300 mL
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- Urine: 800–1500 mL
- Stool: 250 mL
- Insensible loss: 600–900 mL (lungs and skin). (With
fever, each degree above 98.6°F [37°C] adds 2.5
mL/kg/d to insensible losses; insensible losses
are decreased if a patient is undergoing mechanical ventilation;
free water gain can occur from humidified ventilation.)
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Baseline Fluid Requirement
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Afebrile 70-kg Adult:
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If Not a 70-kg Adult:
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Calculate the water requirement according to the following kg method:
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- For the first 10 kg of body weight: 100 mL/kg/d plus
- For the second 10 kg of body weight: 50 mL/kg/d plus
- For the weight above 20 kg: 20 mL/kg/d
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Electrolyte Requirements
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• 70-kg adult, unless otherwise specified
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80–120 mEq/d (children, 3–4 mEq/kg/24
h)
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50–100 mEq/d (children, 2–3 mEq/kg/24
h). In the absence of hypokalemia and with normal renal function,
most of this K is excreted in the urine. Of the total amount of
K, 98% is intracellular, and 2% is extracellular.
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If the serum K level is normal, about 4.5 mEq/L, the
total extracellular pool of K+ = 4.5 × 14
L = 63 mEq. K is easily interchanged between intracellular
and extracellular stores under conditions such as acidemia or alkalemia.
K demands increase with diuresis and building of new body tissues
(anabolic states).
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1–3 g/d, most of which is ...