1. A child vomiting along with a sodium level of 150 MEq/L? What is the expected finding? A. Hypervolemic hypernatremia B. Hypernatremia hyponatremia C. Euvolemic hyponatremia D. Hypovolemic hypernatremia Answer Solution.
Quick answer: A child with vomiting loses fluid (hypotonic losses from the GI tract), leading to volume depletion. If water losses exceed sodium losses, the serum sodium rises above 145 mEq/L. The combination of low volume status + high sodium = Hypovolemic hypernatremia. Answer: D.
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The answer is confirmed across multiple authoritative surgical and medical textbooks. Here is the full explanation:
Answer: D - Hypovolemic Hypernatremia
Why This is the Correct Answer
Step 1: Understand the scenario
- Child with vomiting + serum sodium of 150 mEq/L (normal: 135-145 mEq/L)
- Na > 145 mEq/L = Hypernatremia (eliminates options B and C immediately)
- Vomiting = fluid/volume loss = volume-depleted state
Step 2: Classify the hypernatremia by volume status
Hypernatremia is classified into three categories:
| Type | Volume Status | Causes |
|---|---|---|
| Hypovolemic hypernatremia | Low total body water AND low sodium, but water loss > sodium loss | Vomiting, diarrhea, burns, sweating, diuretics |
| Euvolemic hypernatremia | Normal sodium stores, pure water loss | Diabetes insipidus, fever, insensible losses |
| Hypervolemic hypernatremia | Excess sodium gain | Hypertonic saline, sodium bicarbonate excess |
Step 3: Apply to this case
Vomiting causes loss of hypotonic fluid (gastric contents are hypotonic relative to plasma). This means:
- More water is lost than sodium
- The remaining body fluid becomes relatively concentrated
- Serum sodium rises (hypernatremia)
- Volume is depleted (hypovolemia)
This is the classic mechanism of hypovolemic hypernatremia, confirmed by:
- Tintinalli's Emergency Medicine: "Extrarenal hypovolemic hypernatremia - Vomiting, Diarrhea, GI fistulas, Sweating, Burns"
- Fischer's Mastery of Surgery: "The most common cause is hypovolemic hypernatremia, usually as a result of dehydration due to uncontrolled fluid losses (e.g., diarrhea, high nasogastric tube output, and vomiting)"
- Sabiston Textbook of Surgery: "Hypovolemic hypernatremia commonly occurs in dehydrated patients with low water intake and high fluid losses, such as through vomiting, nasogastric tube loss, or diarrhea"
Why the Other Options are Wrong
- A. Hypervolemic hypernatremia - This occurs when there is excess sodium intake (e.g., hypertonic saline infusion). Vomiting causes volume LOSS, not gain.
- B. Hypernatremia hyponatremia - This is not a valid clinical entity (contradictory terms).
- C. Euvolemic hyponatremia - Sodium is 150 mEq/L here, which is hypernatremia, not hyponatremia. Euvolemic hypernatremia also requires pure water loss without volume depletion (e.g., diabetes insipidus).
Key Concept to Remember
Vomiting = hypotonic fluid loss = more water lost than sodium = volume depletion + rising serum sodium = Hypovolemic Hypernatremia
The correct answer is D. Hypovolemic Hypernatremia.
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