CRNI Fluid and Electrolyte Balance 5 — Questions and Answers
Question 1: A postoperative patient has decreased urine output, pulmonary crackles, and a serum sodium of 148 mEq/L. Which fluid overload pattern does this represent?
- Isotonic fluid excess
- Hypertonic fluid excess (Correct answer)
- Hypotonic fluid deficit
- Isotonic fluid deficit
Correct answer: Hypertonic fluid excess
Elevated sodium with signs of fluid overload indicates hypertonic hypervolemia, often from excessive saline infusion.
Question 2: Which clinical sign best differentiates third-spacing from true dehydration?
- Decreased skin turgor
- Normal or elevated total body water with intravascular deficit (Correct answer)
- Serum sodium above 145 mEq/L
- Elevated hematocrit
Correct answer: Normal or elevated total body water with intravascular deficit
Third-spacing causes intravascular depletion despite normal or increased total body fluid, unlike true dehydration.
Question 3: A patient with SIADH has a urine osmolality of 600 mOsm/kg and serum osmolality of 260 mOsm/kg. What does this indicate?
- Appropriate renal water conservation
- Inappropriate ADH secretion causing concentrated urine despite dilute serum (Correct answer)
- Diabetes insipidus
- Osmotic diuresis
Correct answer: Inappropriate ADH secretion causing concentrated urine despite dilute serum
In SIADH, urine is inappropriately concentrated relative to a dilute serum, reflecting unregulated ADH activity.
Question 4: Which fluid is considered the most physiologically balanced crystalloid for large-volume resuscitation?
- 0.9% NaCl
- D5W
- Plasmalyte or Lactated Ringer's (Correct answer)
- 3% NaCl
Correct answer: Plasmalyte or Lactated Ringer's
Balanced crystalloids like Plasmalyte and Lactated Ringer's closely mimic plasma electrolyte composition and reduce hyperchloremic acidosis risk.
Question 5: A patient with Addison's disease presents with weakness, hypotension, and a serum sodium of 128 mEq/L with potassium of 6.0 mEq/L. What is the underlying fluid-electrolyte mechanism?
- Excess aldosterone causing sodium retention
- Aldosterone deficiency causing sodium loss and potassium retention (Correct answer)
- ADH excess causing free water retention
- Cortisol excess causing hyperglycemia
Correct answer: Aldosterone deficiency causing sodium loss and potassium retention
Aldosterone deficiency in Addison's disease impairs sodium retention and potassium excretion, causing hyponatremia and hyperkalemia.
Question 6: A patient receiving 0.9% NaCl at 200 mL/hr for 12 hours develops a pH of 7.28, HCO3 of 18, and Cl of 116. What has occurred?
- Metabolic alkalosis
- Respiratory acidosis
- Hyperchloremic metabolic acidosis (Correct answer)
- Anion gap metabolic acidosis
Correct answer: Hyperchloremic metabolic acidosis
Large volumes of normal saline cause dilutional hyperchloremic (non-anion gap) metabolic acidosis by lowering bicarbonate relative to chloride.
Question 7: Which assessment parameter is MOST useful for evaluating fluid status in a patient with severe hypoalbuminemia?
- Skin turgor
- Daily weight measurement (Correct answer)
- Serum sodium level
- Blood pressure alone
Correct answer: Daily weight measurement
Daily weight is the most reliable indicator of fluid balance, as hypoalbuminemia causes edema that masks clinical signs of dehydration.
CRNI Fluid and Electrolyte Balance 5
A postoperative patient has decreased urine output, pulmonary crackles, and a serum sodium of 148 mEq/L.
Which fluid overload pattern does this represent?