Useful therapy for hypercyanotic 'tet spells' in patients with tetralogy of Fallot might include any of the following EXCEPT:

Useful therapy for hypercyanotic 'tet spells' in patients with tetralogy of Fallot might include any of the following EXCEPT:

• A. Esmolol
• B. Lactated Ringer's solution bolus (5 mL/kg)
• C. Phenylephrine
• D. Isoproterenol

Answer: (D)

Hypercyanotic spells in tetralogy of Fallot happen when the obstruction to flow from the right ventricle increases and more blood shunts right-to-left across the ventricular septal defect. The goal of therapy is to raise preload and systemic vascular resistance while reducing infundibular spasm, so blood is forced forward into the lungs and oxygenation improves. Giving a crystalloid bolus (like Lactated Ringer’s) increases preload, helping fill the right ventricle and lessen the obstruction. Esmolol is useful because it blunts the infundibular spasm that worsens the obstruction, thereby decreasing the right-to-left shunt. Phenylephrine increases systemic vascular resistance, which also reduces the shunt and improves oxygen delivery to the lungs. Isoproterenol, on the other hand, is a nonselective beta-adrenergic agonist that increases heart rate and contractility and can lower systemic vascular resistance via beta-2 effects. This tends to worsen right-to-left shunting and cyanosis, so it is not a helpful therapy for tet spells.

Hypercyanotic spells in tetralogy of Fallot happen when the obstruction to flow from the right ventricle increases and more blood shunts right-to-left across the ventricular septal defect. The goal of therapy is to raise preload and systemic vascular resistance while reducing infundibular spasm, so blood is forced forward into the lungs and oxygenation improves.

Giving a crystalloid bolus (like Lactated Ringer’s) increases preload, helping fill the right ventricle and lessen the obstruction. Esmolol is useful because it blunts the infundibular spasm that worsens the obstruction, thereby decreasing the right-to-left shunt. Phenylephrine increases systemic vascular resistance, which also reduces the shunt and improves oxygen delivery to the lungs.

Isoproterenol, on the other hand, is a nonselective beta-adrenergic agonist that increases heart rate and contractility and can lower systemic vascular resistance via beta-2 effects. This tends to worsen right-to-left shunting and cyanosis, so it is not a helpful therapy for tet spells.