A baby who was diagnosed with pyloric stenosis has continued to have projectile vomiting. With prolonged vomi… - NORCET 5 Prelims - Sept 2023 (Shift-2)

NORCET 5 Prelims - Sept 2023 (Shift-2)

Child Health Nursing (Pediatrics)

Hard

Appeared in: NORCET 5 Prelims - Sept 2023 (Shift-2)

Explanation

Prolonged projectile vomiting, a hallmark of pyloric stenosis, leads to a significant loss of hydrochloric acid (HCl) from the stomach.
The loss of hydrogen ions (H⁺) and chloride ions (Cl⁻) from the body causes the blood to become more alkaline.
This process results in a specific acid-base disturbance known as metabolic alkalosis.
The body's attempt to compensate can also lead to low levels of potassium (hypokalemia) and chloride (hypochloremia), creating a classic triad of electrolyte imbalances.

Option A: Respiratory acidosis is caused by the retention of carbon dioxide (CO₂) due to inadequate breathing (hypoventilation), not by vomiting. The primary problem in the question is metabolic.
Option B: Respiratory alkalosis is caused by blowing off too much CO₂ through rapid breathing (hyperventilation). Vomiting does not cause hyperventilation.
Option C: Metabolic acidosis is the opposite of metabolic alkalosis. It involves either a loss of bicarbonate or an accumulation of acid in the body. Vomiting causes a loss of acid.

Visual 1: Flowchart: Pyloric Stenosis → Projectile Vomiting → Loss of HCl (H⁺ and Cl⁻) → Increased Blood pH → Metabolic Alkalosis.
Visual 2: Diagram: A four-quadrant chart illustrating the four primary acid-base disorders (Respiratory/Metabolic Acidosis/Alkalosis) with their corresponding pH and PaCO₂/HCO₃⁻ changes.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Acid-base imbalance in pyloric stenosis as background academic context rather than a clinical decision trigger.
The classic electrolyte pattern in an infant with pyloric stenosis is hypochloremic, hypokalemic metabolic alkalosis. Recognizing this is crucial for diagnosis.
It is a patient-safety priority to correct the infant's fluid and electrolyte imbalances before surgical intervention (pyloromyotomy). Anesthesia is unsafe in a patient with significant alkalosis and dehydration.
What if the infant had severe diarrhea instead of vomiting? In that case, the infant would be losing bicarbonate-rich fluid from the intestines, leading to metabolic acidosis, the opposite condition.

How to Approach the Question

Step 1: Identify the core clinical condition and symptom: The question describes an infant with pyloric stenosis and projectile vomiting.
Step 2: Analyze the physiological consequence of the symptom. Vomiting causes the loss of stomach contents.
Step 3: Recall the composition of stomach contents. The stomach is highly acidic, containing hydrochloric acid (HCl).
Step 4: Determine the effect of losing acid. Losing a large amount of acid (H⁺ ions) makes the blood more basic, or alkaline.
Step 5: Differentiate between metabolic and respiratory causes. Since the problem originates from the gastrointestinal system (a metabolic function), it is a metabolic disturbance.
Step 6: Combine the findings. The loss of acid from a metabolic source leads to metabolic alkalosis. Select the option that matches this conclusion.

Concept Tested & Keywords

Concept Tested: Acid-base imbalance in pyloric stenosis
Stem keywords: pyloric stenosis, projectile vomiting, prolonged vomiting, infant
Lead-in keywords: prone to
Clinical cues: The key clinical cue is 'projectile vomiting', which points to a significant loss of gastric acid.

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