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Difficulty: MediumPediatric Cardiovascular Disorders

A 9-month-old boy arrives at the emergency department accompanied by his parents after a frightening episode at home. His mother reports that while he was crying vigorously during a diaper change, his lips, hands, and feet suddenly turned a deep blue color, and he appeared unusually limp. The mother instinctively held him tightly with his knees tucked against his chest, and his normal skin color slowly returned over 15 minutes. The infant was diagnosed with a heart murmur in the neonatal nursery but missed his scheduled cardiology follow-up. Current vital signs are temperature 37.0°C (98.6°F), heart rate 138/min, respiratory rate 32/min, and blood pressure 94/56 mm Hg. Oxygen saturation is 93% on room air. Cardiac auscultation reveals a prominent right ventricular heave, a single S2, and a grade 3/6 harsh, crescendo-decrescendo systolic murmur heard best at the left mid-to-upper sternal border. The remainder of the physical examination is unremarkable. If a similar hypercyanotic episode occurs during evaluation and fails to improve with supplemental oxygen and knee-chest positioning, which of the following is the most appropriate next pharmacologic step in management?

  1. A
    Intravenous furosemide
  2. B
    Continuous infusion of prostaglandin E1
  3. Intravenous morphine sulfateAnswer
  4. D
    Intravenous digoxin
  5. E
    Inhaled racemic epinephrine

Answer

Intravenous morphine sulfate is the most appropriate next pharmacologic step for a hypercyanotic spell refractory to initial positioning and oxygen.
The correct approach for a hypercyanotic 'tet spell' that fails initial conservative measures includes administering intravenous morphine. Morphine acts by depressing the respiratory center to reduce hyperpnea, decreasing systemic sympathetic tone, and subsequently reducing the infundibular spasm that causes the right-to-left shunt.

Step-by-Step Solution

1
Identify the underlying congenital heart defect based on the clinical presentation.
The patient has Tetralogy of Fallot (ToF), suggested by the history of a neonatal murmur, a hypercyanotic 'tet spell' relieved by knee-chest positioning, a right ventricular heave, and a harsh systolic ejection murmur at the left upper sternal border indicating right ventricular outflow tract obstruction.
Accurate diagnosis is required to understand the specific pathophysiology of the acute decompensation.
2
Determine the pathophysiology of the acute hypercyanotic episode.
The spell is caused by an acute increase in right ventricular outflow tract (RVOT) resistance (infundibular spasm) or a decrease in systemic vascular resistance (SVR), forcing deoxygenated blood across the ventricular septal defect into the systemic circulation (right-to-left shunt).
Management must directly reverse these specific hemodynamic changes.
3
Select the appropriate pharmacologic intervention for a refractory spell.
After knee-chest positioning (which increases SVR) and oxygen (which decreases pulmonary vascular resistance), intravenous morphine is given to decrease sympathetic tone and hyperpnea, thereby relaxing the RVOT.
Medications that increase contractility, decrease preload, or decrease SVR are strictly contraindicated.

Key Concept

Hypercyanotic 'tet spells' in Tetralogy of Fallot are managed initially by increasing systemic vascular resistance (knee-chest positioning) and providing oxygen, followed by medications that decrease sympathetic drive and relax the right ventricular outflow tract, such as intravenous morphine or beta-blockers.

Alternative Method

If intravenous access is difficult to obtain during the acute spell, intramuscular morphine or intranasal fentanyl can be utilized. Additionally, rapid intravenous fluids (crystalloid bolus) are crucial to increase preload and widen the right ventricular outflow tract.
Estimated Time:1m 15s
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Topics

Pediatric Cardiovascular Disorders

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