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Difficulty: MediumPediatric Cardiovascular Disorders

An 8-month-old infant is rapidly triaged in the emergency department following a syncopal event at home. According to the parents, the child was crying vigorously during a diaper change when he suddenly became deeply blue around the lips and face, followed by a brief loss of consciousness. The mother notes he has had similar, though milder, episodes of blueness when agitated over the past few weeks. The infant was born at a rural clinic and has not received subsequent medical care. On physical examination, the infant is awake but severely agitated. Vital signs demonstrate a heart rate of 180/min, respiratory rate of 55/min, and oxygen saturation of 74% on room air. Auscultation reveals a prominent right ventricular impulse and a harsh, crescendo-decrescendo systolic murmur at the left upper sternal border. Lung fields are clear to auscultation. Which of the following is the most appropriate initial step in the management of this patient?

  1. A
    Initiate noninvasive positive pressure ventilation
  2. B
    Administer nebulized albuterol sulfate
  3. C
    Transport the patient for urgent computed tomography angiography of the chest
  4. Position the patient with the knees flexed firmly against the abdomenAnswer
  5. E
    Begin empiric broad-spectrum intravenous antimicrobial therapy

Answer

Position the patient with the knees flexed firmly against the abdomen
The patient is experiencing a hypercyanotic ('Tet') spell, characterized by a sudden increase in right-to-left shunting through a ventricular septal defect due to dynamic right ventricular outflow tract (RVOT) obstruction. The harsh, crescendo-decrescendo systolic murmur at the left upper sternal border is characteristic of the RVOT obstruction seen in Tetralogy of Fallot. The most appropriate initial step is positioning the patient with the knees flexed firmly against the abdomen (knee-chest position). This mechanical maneuver compresses the femoral arteries, thereby increasing systemic vascular resistance (SVR). The elevated SVR increases left ventricular afterload, which decreases the right-to-left shunt and forces more blood across the RVOT into the pulmonary circulation, rapidly improving arterial oxygenation.

Step-by-Step Solution

1
Analyze the clinical presentation to establish a preliminary diagnosis.
The infant exhibits cyanosis triggered by crying, a harsh crescendo-decrescendo systolic murmur at the left upper sternal border, and a right ventricular impulse.
These are classic signs of Tetralogy of Fallot, suggesting the infant is experiencing an acute hypercyanotic ('Tet') spell.
2
Identify the underlying pathophysiologic mechanism of the acute deterioration.
Agitation and crying lead to increased endogenous catecholamines.
This causes spasm of the right ventricular outflow tract (RVOT) and a drop in systemic vascular resistance (SVR), forcing deoxygenated blood through the ventricular septal defect into the systemic circulation.
3
Determine the most appropriate immediate physiological intervention.
The first-line management is the knee-chest position.
Kinking the femoral arteries mechanically increases SVR, which counteracts the right-to-left shunt and directs more blood into the pulmonary circulation for oxygenation.

Key Concept

Hypercyanotic (Tet) spells in Tetralogy of Fallot are initially managed with the knee-chest position to mechanically increase systemic vascular resistance and reduce right-to-left shunting.
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Topics

Pediatric Cardiovascular Disorders

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