A baby who was diagnosed with pyloric stenosis has continued to have projectile vomiting. With prolonged vomiting, the baby is prone to?

1. A

   Respiratory acidosis

2. B

   Respiratory alkalosis

3. C

   Metabolic acidosis

4. D

   Metabolic alkalosis

Appeared in: NORCET 6 mains-2024

Explanation

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• Prolonged projectile vomiting, a hallmark of pyloric stenosis, causes a significant loss of gastric acid (hydrochloric acid, HCl).
• The loss of hydrogen ions (H+) from the body leads to a decrease in overall acidity and a corresponding rise in blood pH, resulting in alkalosis.
• Because the root cause is a disturbance in the body's metabolic processes (loss of acid and electrolytes from the GI tract) rather than a primary respiratory issue, the condition is termed metabolic alkalosis.
• This process is often accompanied by the loss of chloride and potassium, leading to the classic presentation of hypochloremic, hypokalemic metabolic alkalosis.

Why Other Options Were Wrong

• Option A: Respiratory acidosis is incorrect. This condition is caused by the retention of carbon dioxide (CO2) due to inadequate breathing (hypoventilation), which lowers the blood pH.
• Option B: Respiratory alkalosis is incorrect. This is caused by excessive loss of CO2 from rapid breathing (hyperventilation), which raises the blood pH.
• Option C: Metabolic acidosis is the opposite of what occurs with vomiting. It involves a decrease in blood pH due to either an accumulation of acid or a loss of bicarbonate (a base).

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Acid-base imbalance resulting from prolonged vomiting in pyloric stenosis as background academic context rather than a clinical decision trigger.
• Nurses must closely monitor the fluid and electrolyte status of infants with pyloric stenosis, as dehydration and alkalosis can develop rapidly and become life-threatening.
• A key nursing responsibility is the pre-operative correction of these imbalances. This involves administering intravenous fluids with appropriate electrolytes (sodium, chloride, and potassium) to stabilize the infant for surgery (pyloromyotomy).
• Accurate intake and output monitoring, including the frequency and volume of emesis, is crucial for assessing the degree of dehydration and ongoing fluid loss.

How to Approach the Question

• First, identify the core clinical condition mentioned: Pyloric stenosis.
• Next, identify the key symptom and its characteristic: Prolonged, projectile vomiting.
• Analyze the physiological effect of this symptom. Vomiting expels contents from the stomach.
• Recall the primary component of stomach fluid: Hydrochloric acid (HCl).
• Determine the consequence of losing a large amount of acid (H+ ions): The body's pH will increase, leading to a state of alkalosis.
• Finally, differentiate between metabolic and respiratory causes. Since the problem originates from the gastrointestinal system (a metabolic process), the correct answer is metabolic alkalosis.

Concept Tested & Keywords

• Concept Tested: Acid-base imbalance resulting from prolonged vomiting in pyloric stenosis
• Stem keywords: pyloric stenosis, projectile vomiting, prolonged vomiting
• Lead-in keywords: prone to
• Clinical cues: Diagnosis: Pyloric stenosis - This condition is characterized by forceful vomiting, which is the primary cause of the imbalance.
• Clinical cues: Symptom: Projectile vomiting - This specific type of vomiting indicates a significant and forceful loss of gastric contents, rich in acid.

Question ID

QlnlCQAvpkoINrfZnXKq7c

Copy ID

Reference Book

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 pp. 563-565, 559-561, 1062-1064