Question
A young patient presents with muscle spasms, numbness in the hands and feet, seizures, and difficulty in breathing due to laryngospasm. His blood work reveals an electrolyte imbalance. What is the most likely cause of these manifestations?
| A. |
Respiratory Acidosis
|
| B. |
Respiratory Alkalosis
|
| C. |
Metabolic Acidosis
|
| D. |
Metabolic Alkalosis
|
Show Answer
|
Correct Answer » B
Explanation
|
|
- Respiratory alkalosis results from hyperventilation, causing a decrease in arterial carbon dioxide (PaCO₂).
- The increase in blood pH causes more calcium to bind to albumin, thereby reducing ionized (free) calcium levels.
- Although total serum calcium remains normal, the decrease in ionized calcium produces symptoms of acute hypocalcemia.
These manifestations include:
- Perioral numbness
- Paresthesias of the hands and feet
- Muscle cramps
- Carpopedal spasm
- Tetany
- Laryngospasm
- Seizures
Explanation of the Correct Answer
B. Respiratory alkalosis
Mechanism:
- Hyperventilation → ↓ PaCO₂
- Increased blood pH
- Increased calcium binding to albumin
- Decreased ionized calcium
- Increased neuromuscular excitability
- Tetany, laryngospasm, and seizures
Common causes include:
- Anxiety or panic attacks
- Pain
- Fever
- Pregnancy
- High altitude
- Mechanical overventilation
- Early salicylate poisoning
Why Other Options are Incorrect
A. Respiratory acidosis
- Caused by hypoventilation and CO₂ retention.
- Produces CNS depression, headache, confusion, and drowsiness rather than tetany.
- Does not decrease ionized calcium.
C. Metabolic acidosis
- Characterized by decreased blood pH.
- Patients develop Kussmaul respiration as compensation.
- Acidosis increases ionized calcium rather than decreasing it, making tetany unlikely.
D. Metabolic alkalosis
- Metabolic alkalosis can also reduce ionized calcium and produce tetany.
- However, in a young patient with hyperventilation-related symptoms, respiratory alkalosis is the more likely diagnosis.
- If the question specifically mentioned vomiting, diuretic use, or gastric suction, metabolic alkalosis would be more likely.
