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What percentage of body weight is fluid?
- 60%
- (40 intracellular, 20 extracellular)
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How many liters of blood are in a 70 kg man?
5 (blood is approximately 7% of TBW)
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Water requirement per 24 hours?
30-35 mL/kg
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Potassium requirement per 24 hours?
1 mEq/kg
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Chloride requirement per 24 hours?
1.5 mEq/kg
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Sodium requirement per 24 hours?
1-2 mEq/kg
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When does third spacing occur post-operatively?
On about the 3rd post-op day, fluid that moved into the extravascular space begins to move back into the intravascular space. Beware of fluid overload.
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What are classic signs of third-spacing?
- Tachycardia
- Decreased urine output
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Causes of metabolic acidosis
- Loss of bicarb (diarrhea, ileus, fistula, high-output ileostomy, carbonic anhydrase inhibitors)
- Gain of acid (ischemia, renal failure, ketoacidosis, necrosis)
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What causes hypokalemic hypochloremic alkalosis?
NGT suction or loss of gastric acid (vomiting, NGT)
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Why does NGT suctioning cause hypokalemia?
Loss of gastric HCl results in alkalosis. In response, H+ is driven out of the cells, into the interstitium, in exchange for K+. K+ is also lost in the kidneys, in exchange for Na+.
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What is paradoxic alkalotic aciduria?
In severe vomiting, there is metabolic alkalosis due to loss of gastric acid, but there is also acidification of the urine, due to loss of H+ in exchange for Na, in an attempt to restore intravascular volume.
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What is the most significant cause of insensible fluid loss?
- Respiration--500-700 mL are lost, per 24 hours
- Respiratory fluid loss increases with fever and tachypnea
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