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1. How can fluid cross between fluid compartments? What does this depend on?
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Correct answer:
Fluid can cross compartments by osmosis, which depends on a solute gradient, and filtration, which is a result of a hydrostatic pressure gradient.
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2. Is the electrolyte composition of each fluid compartment the same?
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Correct answer:
No, it is different.
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3. How can you calculate daily fluid and electrolyte requirements?
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Correct answer:
In order to calculate daily fluid and electrolyte requirements, the daily losses should be measured or estimated.
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4. How are fluid losses from the kidney regulated in the absence of intrinsic renal disease?
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Correct answer:
By aldosterone and antidiuretic hormone.
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5. Why are aldosterone and antidiuretic hormone so important?
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Correct answer:
These two hormone systems regulate the circulating volume and its osmolarity, and are thus crucial to homeostasis.
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6. What is the role of the kidneys in normal fluid losses?
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Correct answer:
The kidneys control water and electrolyte balance closely, and can function in spite of extensive renal disease, and abuse from doctors prescribing intravenous fluids. However, damaged kidneys leave the patient exquisitely vulnerable to inappropriate water and electrolyte administration.
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7. What are the main abnormal causes of increased losses of fluid from the kidney?
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Correct answer:
Impaired tubular function may cause increased losses. Resolving acute tubular necrosis, diabetes insipidus and head injury may result in loss of several litres of dilute urine.
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8. What are the main abnormal causes of water retention and haemodilution?
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Correct answer:
Production of antidiuretic hormone (ADH) by tumours (the syndrome of inappropriate ADH; SIADH) causes water retention and haemodilution.
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9. What are the values of sodium, chloride, potassium, bicarbonate and calcium in 4% dextrose or 0.18% saline?
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Correct answer:
30 mmol/L of sodium, 30 mmol/L of chloride, nothing else is in it.
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10. What is the general rule of thumb when giving intravenous fluids?
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Correct answer:
Replace half the estimated loss quickly, and then reassess before replacing the rest.
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11. Which measurement can give you a good guide as to the rate of fluid replacement needed?
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Correct answer:
Central venous pressure monitoring will help in the adjustment of rate of infusion.
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12. Why is it important to have good nutritional status before surgery?
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Correct answer:
Patients with poor nutritional states have lowered resistance to infection and impaired wound healing.
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13. What are the basic contents of parenteral nutrition?
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Correct answer:
- The principle is to provide the patient with protein in the form of amino acids, carbohydrate in the form of glucose, and fat emulsions such as Intralipid.
- Energy is derived from the carbohydrate and fat (30–50% fat), which must be given when amino acids are given, usually in a ratio of 1000 kJ/g protein nitrogen.
- Trace elements, such as zinc, magnesium and copper, as well as vitamins such as vitamin B12 and ascorbic acid, and the lipid-soluble vitamins A, D, E and K, are usually added to the fluid, which is infused as a 2.5 litres volume over 24 hours.
