Should fluids be administered to a hypotensive patient with tetralogy of Fallot?

Management of Hypotension in Tetralogy of Fallot

Fluid administration should be avoided in a hypotensive patient with tetralogy of Fallot, as it may worsen the right ventricular outflow tract obstruction and increase right-to-left shunting, potentially worsening hypoxemia and hypotension. 1

Pathophysiology of Hypotension in Tetralogy of Fallot

Tetralogy of Fallot is characterized by four key components:

• Ventricular septal defect (VSD)
• Right ventricular outflow tract obstruction
• Overriding aorta
• Right ventricular hypertrophy

In these patients, hypotension can trigger a dangerous cycle:

• Decreased systemic vascular resistance leads to increased right-to-left shunting through the VSD
• This causes worsening hypoxemia and cyanosis
• Infundibular spasm can occur, further obstructing right ventricular outflow

First-Line Management

1. Position the patient in a knee-chest position to increase systemic vascular resistance
2. Administer phenylephrine to increase systemic vascular resistance and reduce right-to-left shunting
3. Consider ketamine for infundibular spasm (hypercyanotic spell) at 1-2 mg/kg IV, titrating repeat doses to desired effect 1
4. Avoid volume administration as this can worsen right-to-left shunting

Second-Line Management

If the patient remains hypotensive despite the above measures:

1. Initiate norepinephrine at 0.05-2 mcg/kg/min, titrated to maintain adequate blood pressure 2

   • Norepinephrine increases systemic vascular resistance which reduces right-to-left shunting
   • Target a systolic blood pressure appropriate for age (for a 7-year-old: >70 + (2 × age in years) = >84 mmHg) 1

2. Consider morphine to reduce pulmonary vascular resistance and anxiety, which can worsen infundibular spasm

3. Provide supplemental oxygen at 6-8 L/min to improve oxygen saturation 1

Special Considerations

• Avoid fluid boluses which can increase right ventricular volume and worsen right-to-left shunting
• Monitor for acidosis which can worsen pulmonary vasoconstriction
• Evaluate for precipitating causes of hypotension such as arrhythmias, which are common in patients with tetralogy of Fallot 1
• Consider echocardiography to assess the severity of right ventricular outflow tract obstruction and degree of right-to-left shunting 1

Common Pitfalls

1. Administering fluid boluses - This is a common error in managing hypotensive patients but can be detrimental in tetralogy of Fallot by increasing right-to-left shunting

2. Failing to recognize "masked hypotension" - Elevated central venous pressure in these patients can artificially increase mean arterial pressure, concealing the true severity of hypotension 3

3. Delaying vasopressor therapy - Early use of vasopressors to increase systemic vascular resistance is critical in these patients

4. Overlooking the need for definitive management - While acute management focuses on stabilizing hemodynamics, these patients often require cardiac catheterization or surgical intervention to address the underlying cardiac defects 1

In summary, the management of hypotension in a patient with tetralogy of Fallot requires increasing systemic vascular resistance with vasopressors rather than administering fluids, which could worsen the patient's condition by increasing right-to-left shunting.