Question:
A child with Tetralogy of Fallot (TOF) develops a cyanotic (hypercyanotic) spell. Which of the following measures helps to relieve the spell?
A child with Tetralogy of Fallot (TOF) develops a cyanotic (hypercyanotic) spell. Which of the following measures helps to relieve the spell?
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Management of a Tet Spell: Knee-chest position (squatting) to increase SVR, $100\%$ Oxygen, Morphine (decreases respiratory drive/agitation), IV Fluids, and Beta-blockers (Propranolol) to relieve infundibular spasm.
Updated On: Sep 3, 2026
- Fever
- Agitation
- Vigorous physical activity
- Squatting
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The Correct Option is D
Solution and Explanation
Concept:
A child diagnosed with Tetralogy of Fallot is experiencing an acute "Tet spell," a dangerous episode of profound hypoxemia.
The clinical task is to identify the specific physical maneuver (or physiological state) that acutely reverses the right-to-left shunting responsible for the cyanosis.
Explanation:
• Tetralogy of Fallot (TOF) comprises four defects: a large Ventricular Septal Defect (VSD), overriding aorta, right ventricular hypertrophy, and Right Ventricular Outflow Tract (RVOT) obstruction (infundibular stenosis).
• A hypercyanotic or "Tet" spell is an acute, life-threatening episode characterized by sudden, profound cyanosis, irritability, hyperventilation, and occasionally syncope.
• The pathophysiology of a Tet spell is driven by a sudden, severe spasm of the infundibular muscle, drastically worsening the RVOT obstruction. Simultaneously, events that cause a drop in Systemic Vascular Resistance (SVR)—such as agitation, crying, fever, or physical exertion—exacerbate the condition.
• When SVR drops and RVOT obstruction increases, deoxygenated blood in the right ventricle is forced entirely through the VSD into the aorta (a massive Right-to-Left shunt), entirely bypassing the lungs and causing severe systemic hypoxia.
• Squatting (or placing an infant in a knee-to-chest position) is a highly effective, natural compensatory maneuver performed by older children to abort a spell.
• Squatting physically kinks the large femoral and popliteal arteries in the legs. This mechanically and immediately causes a massive increase in Systemic Vascular Resistance (SVR) and left ventricular pressure.
• The sudden rise in left-sided pressures opposes and overcomes the Right-to-Left shunt at the VSD, forcing the deoxygenated blood back through the narrowed pulmonary tract to the lungs for oxygenation, thereby relieving the cyanosis.
• Fever (Option A), agitation (Option B), and vigorous physical activity (Option C) all decrease SVR and increase oxygen demand, which actively precipitates and severely worsens a Tet spell.
Final Answer:
Squatting successfully relieves a hypercyanotic spell by mechanically increasing systemic vascular resistance and decreasing the right-to-left shunt.
A child diagnosed with Tetralogy of Fallot is experiencing an acute "Tet spell," a dangerous episode of profound hypoxemia.
The clinical task is to identify the specific physical maneuver (or physiological state) that acutely reverses the right-to-left shunting responsible for the cyanosis.
Explanation:
• Tetralogy of Fallot (TOF) comprises four defects: a large Ventricular Septal Defect (VSD), overriding aorta, right ventricular hypertrophy, and Right Ventricular Outflow Tract (RVOT) obstruction (infundibular stenosis).
• A hypercyanotic or "Tet" spell is an acute, life-threatening episode characterized by sudden, profound cyanosis, irritability, hyperventilation, and occasionally syncope.
• The pathophysiology of a Tet spell is driven by a sudden, severe spasm of the infundibular muscle, drastically worsening the RVOT obstruction. Simultaneously, events that cause a drop in Systemic Vascular Resistance (SVR)—such as agitation, crying, fever, or physical exertion—exacerbate the condition.
• When SVR drops and RVOT obstruction increases, deoxygenated blood in the right ventricle is forced entirely through the VSD into the aorta (a massive Right-to-Left shunt), entirely bypassing the lungs and causing severe systemic hypoxia.
• Squatting (or placing an infant in a knee-to-chest position) is a highly effective, natural compensatory maneuver performed by older children to abort a spell.
• Squatting physically kinks the large femoral and popliteal arteries in the legs. This mechanically and immediately causes a massive increase in Systemic Vascular Resistance (SVR) and left ventricular pressure.
• The sudden rise in left-sided pressures opposes and overcomes the Right-to-Left shunt at the VSD, forcing the deoxygenated blood back through the narrowed pulmonary tract to the lungs for oxygenation, thereby relieving the cyanosis.
• Fever (Option A), agitation (Option B), and vigorous physical activity (Option C) all decrease SVR and increase oxygen demand, which actively precipitates and severely worsens a Tet spell.
Final Answer:
Squatting successfully relieves a hypercyanotic spell by mechanically increasing systemic vascular resistance and decreasing the right-to-left shunt.
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