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Difficulty: EasyNephrology

Match each clinical scenario with the primary acid-base disorder it most likely causes.

  • A 25-year-old with severe watery diarrhea for 3 daysNormal anion gap metabolic acidosis
  • A 40-year-old with recurrent vomiting due to gastric outlet obstructionMetabolic alkalosis
  • A 30-year-old with an opiate overdose and a respiratory rate of 6 breaths/minRespiratory acidosis
  • A 22-year-old hyperventilating during a severe panic attackRespiratory alkalosis

Answer

Diarrhea matches with Normal anion gap metabolic acidosis. Vomiting matches with Metabolic alkalosis. Opiate overdose matches with Respiratory acidosis. Panic attack matches with Respiratory alkalosis.
The diagnosis of primary acid-base disorders requires identifying the underlying pathophysiology. Loss of bicarbonate-rich fluids (such as in severe diarrhea) leads to normal anion gap metabolic acidosis. Loss of hydrogen ions (such as in vomiting) leads to metabolic alkalosis. Decreased alveolar ventilation (such as in opiate toxicity) causes carbon dioxide retention and respiratory acidosis. Increased alveolar ventilation (such as in anxiety or panic attacks) blows off excessive carbon dioxide, causing respiratory alkalosis.

Step-by-Step Solution

1
Analyze the acid-base effect of lower gastrointestinal fluid loss.
Severe diarrhea causes bicarbonate loss, which matches with normal anion gap metabolic acidosis.
Lower GI secretions are rich in bicarbonate, and their loss forces the kidneys to reabsorb chloride to maintain electroneutrality, causing a hyperchloremic (normal anion gap) metabolic acidosis.
2
Analyze the acid-base effect of upper gastrointestinal fluid loss.
Vomiting causes acid loss, which matches with metabolic alkalosis.
Gastric fluid is rich in hydrochloric acid; its loss directly increases serum bicarbonate concentration, leading to alkalosis.
3
Analyze the acid-base effect of central respiratory depression.
An opiate overdose causes hypoventilation, which matches with respiratory acidosis.
A respiratory rate of 6 breaths/min indicates severe hypoventilation, leading to the accumulation of carbon dioxide (PCO2) in the blood.
4
Analyze the acid-base effect of hyperventilation.
A panic attack causes excessive breathing, which matches with respiratory alkalosis.
Hyperventilation drives off carbon dioxide at a rate faster than it is produced by cellular metabolism, causing a primary decrease in PCO2.

Key Concept

Primary acid-base disorders based on classic clinical presentations
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Topics

Nephrology

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