What medications can help with positive pressure ventilation (PPV) in Fontan patients?

Medications to Help Positive Pressure Ventilation in Fontan Patients

For Fontan patients requiring positive pressure ventilation, hypoventilation strategies and systemic vasodilators should be prioritized to optimize hemodynamics and reduce mortality risk. 1, 2

Understanding Fontan Physiology and PPV Challenges

Fontan circulation creates a unique hemodynamic situation where:

• Pulmonary blood flow depends on passive venous return without a subpulmonary ventricle
• Positive pressure ventilation can impair venous return, reducing preload and cardiac output
• Small increases in pulmonary vascular resistance (PVR) can dramatically impact cardiac performance

First-Line Medication Strategies

1. Systemic Vasodilators

• α-adrenergic antagonists (e.g., phenoxybenzamine): First-line therapy to reduce systemic vascular resistance, improve systemic oxygen delivery, and reduce cardiac arrest risk (Class IIa, LOE B) 1, 2
• Other vasodilators: Milrinone or nitroprusside for patients with excessive pulmonary-to-systemic flow ratio (Qp:Qs) (Class IIa, LOE B) 1, 2

2. Ventilation Strategies with Medication Support

• Deliberate hypoventilation: Target PaCO2 of 50-60 mmHg to improve oxygen delivery (Class IIa, LOE B) 1
  • Can be achieved by:
    • Reducing minute ventilation
    • Increasing inspired CO2 fraction
    • Administering opioids with or without chemical paralysis 1

3. Pulmonary Vasodilators

• Inhaled nitric oxide (iNO): Reduces pulmonary vascular resistance (Class IIa, LOE C) 1
• Aerosolized prostacyclin or analogs: Alternative to iNO (Class IIa, LOE C) 1
• IV prostacyclin: Consider if iNO unavailable (Class IIa, LOE C) 1
• Sildenafil (PDE-5 inhibitor): Improves pulmonary blood flow and exercise capacity in Fontan patients 1, 3
• Bosentan: May improve oxygen saturation and exercise tolerance in Fontan patients 1

Medication Considerations During PPV

1. Avoid excessive sedation that might worsen respiratory drive

   • When using opioids for hypoventilation strategy, carefully titrate to avoid respiratory depression
   • If benzodiazepines are needed, titrate midazolam carefully with reduced dosing 4

2. Inotropic support may be needed but use with caution:

   • Low-dose dopamine (3 mcg/kg/min) can support cardiac output 5
   • Avoid pure β-adrenergic agonists that may increase heart rate without improving stroke volume

3. Reinstitute any interrupted pulmonary vasodilator therapy if the patient was previously receiving it (Class IIa, LOE C) 2

Advanced Management for Refractory Cases

• Consider ECMO for patients with persistent cardiac arrest or severe hemodynamic compromise (Class IIa, LOE C) 1, 2
• Transition to negative-pressure ventilation when possible, as it improves cardiac output compared to positive pressure ventilation (Class IIa, LOE C) 1, 5

Key Pitfalls to Avoid

1. Excessive positive pressure: Even small increases in intrathoracic pressure can dramatically reduce venous return and cardiac output in Fontan circulation 5

2. Overventilation: Excessive ventilation reduces cerebral oxygenation and can worsen cardiac output in BDG circulation 1

3. Ignoring diastolic dysfunction: Reduced ventricular compliance is an important component of Fontan dysfunction and can be exacerbated during stress 6

4. Overlooking collateral flow: Aortopulmonary collateral flow contributes substantially to pulmonary flow during stress and should be considered when assessing hemodynamics 6

The management of Fontan patients requiring PPV requires careful attention to their unique physiology. By focusing on reducing PVR, optimizing ventilation strategies, and supporting cardiac output, clinicians can improve outcomes in this challenging patient population.