What is the treatment for hypotension in a pediatric patient with Fontan circulation?

Treatment of Hypotension in Pediatric Patients with Fontan Circulation

For pediatric patients with Fontan circulation experiencing hypotension, systemic vasodilators such as α-adrenergic antagonists (e.g., phenoxybenzamine) should be used to treat increased systemic vascular resistance, improve systemic oxygen delivery, and reduce the likelihood of cardiac arrest. 1

Understanding Fontan Physiology and Hypotension

The Fontan circulation creates a critical bottleneck with:

• Upstream congestion
• Downstream decreased flow
• Limited cardiac output control
• Chronic preload deprivation with increasing filling pressures

These unique hemodynamic features require specific management approaches that differ from standard hypotension treatment.

Initial Assessment and Management Algorithm

1. Assess for signs of Fontan failure:

   • Mental status changes
   • Peripheral perfusion
   • Urine output
   • Distal pulses
   • Heart rate

2. First-line interventions:

   • Cautious fluid resuscitation: Use smaller boluses (5-10 mL/kg) of isotonic crystalloids to avoid worsening venous congestion 2
   • Consider hypoventilation: Deliberately increase PaCO2 to 50-60 mmHg to improve oxygen delivery in patients with Fontan physiology (Class IIa, LOE B) 1
   • Reinstitute any interrupted pulmonary vasodilator therapy if the patient was previously receiving it (Class IIa, LOE C) 1

3. Pharmacologic management:

   • Systemic vasodilators: α-adrenergic antagonists like phenoxybenzamine (Class IIa, LOE B) 1
   • Additional vasodilator options: Milrinone or nitroprusside (nipride) to reduce systemic vascular resistance (Class IIa, LOE B) 1
   • Pulmonary vasodilators: Consider inhaled nitric oxide or aerosolized prostacyclin to reduce pulmonary vascular resistance 1
   • PDE5 inhibitors: Consider sildenafil, particularly for patients with chronic Fontan circulation issues 3

4. Advanced measures for refractory hypotension:

   • Negative-pressure ventilation if available to improve cardiac output (Class IIa, LOE C) 1
   • Consider ECMO for patients with persistent cardiac arrest or severe hemodynamic compromise (Class IIa, LOE C) 1

Key Considerations for Fontan Patients

• Avoid excessive positive pressure ventilation: This can impair venous return and worsen cardiac output 1
• Monitor for protein-losing enteropathy and ascites: These are markers of Fontan failure and may require more aggressive therapy 3
• Fluid management is critical: Excessive fluid can worsen venous congestion, while insufficient fluid can compromise preload 2
• Response to fluid boluses may be transient: Peak response typically occurs shortly after administration and may return to baseline 2

Common Pitfalls to Avoid

1. Excessive positive pressure ventilation: Can impede venous return and worsen cardiac output in Fontan circulation
2. Standard vasopressor use: Traditional vasopressors like norepinephrine may increase systemic vascular resistance and worsen Fontan physiology
3. Aggressive fluid resuscitation: Can worsen venous congestion without improving cardiac output
4. Ignoring pulmonary vascular resistance: In Fontan patients, pulmonary vascular impedance is a major determinant of outcome 4
5. Failing to consider ECMO early: For severe hemodynamic compromise, early consideration of mechanical support may be life-saving

By following this algorithm and understanding the unique physiology of the Fontan circulation, clinicians can effectively manage hypotension in these complex patients and improve outcomes.