Fontan Circulation

This covers physiology and principles of management of the Fontan circulation. Operative elements are covered briefly under the univentricular pathway.

The Fontan Circulation is a single-ventricle circulation. In the Fontan:

• Blood flows:
  • From the SVC/IVC directly to the pulmonary artery
    Pulmonary flow is passive.
  • Pulmonary circulation returns blood to the single, “left”/systemic atrium
  • Systemic ventricle to systemic circulation
• The critical bottleneck to flow occurs in the pulmonary circulation
  Therefore cardiac output and ventricular filling are dependent on pulmonary impedance, and:
  • Venous congestion occurs upstream, and is independent of cardiac output
  • Cardiac function is not the determinant of cardiac output
    
  • Circulation is dependent on a low PVR
• A fenestration between the IVC and systemic atria
  • Allows some ventricular filling to occur if PVR ↑
  • Reduces venous congestion and associated complications
  • Leads to a degree of cyanosis

Management

Treatment strategies must address the critical bottleneck to be effective:

• Reduce venous congestion
  Chronically elevated CVP is poorly tolerated.
  • Complications occur due to ↑ pressures
  • Filling in excess of what the pulmonary bottleneck can utilise will not augment circulatory parameters
  • Diuretics may be effective
• Reduce PVR

Anaesthetic Considerations

• B
  • Low PVR
    Minimisation of TPG is critical to maintain systemic ventricular filling. Avoid:
    • ↑ PCO₂
    • ↓ PO₂
    • ↓ Temperature
    • ↓ pH
  • Minimise Pip
    High airway pressures result in cessation of pulmonary flow, and ventricular filling is fenestration dependent. Therefore:
    • Negative-pressure ventilation is beneficial to maintain ventricular filling
    • If positively pressure-ventilating:
      • Avoid excessive PEEP
      • Minimise I time/Prolong E time
        As soon as Pip exceeds CVP then there will be no pulmonary flow. Therefore, the absolute inspiratory pressure is essentially irrelevant, as CVP is usually only mildly elevated and so any inspiratory pressure (however low) will prevent pulmonary flow.
• C
  • Arterial line is mandatory
  • Adequate preload
    
    • Ensure adequately resuscitated pre-operatively
    • Fill in anticipation of venodilation post-induction
  • Optimal filling pressures
    Other factors affecting filling pressure are important to optimise. Consider:
    • Valvular function
    • Ventricular function
    • Maintain sinus rhythm
    • Optimise afterload
• E
  • Position to optimise venous return

Marginal and Ineffective Therapies

Treatments that don’t affect the critical bottleneck:

• Chronotropes
• Inotropes
• Afterload reduction

Complications

Although a palliative procedure, outcomes vary widely and quality of life may be high for several decades. Potential complications include:

• Death
  Usually due to gradual elevation in:
  • Ventricular filling pressures
  • PVR
• Arrhythmia
• Secondary to intrinsic properties of the circulation
  • Cardiac failure
    
    • Diastolic dysfunction
      Combination of:
      • Volume overload of the single ventricle, particular during the BDCPC/S stage
      • Volume underload of the single ventricle, after establishment of the Fontan
    • Systolic dysfunction
      Pressure overload of the single ventricle in the low-volume, low-compliance post-Fontan stage.
  • Reduced exercise capacity
    Unable to ↑ CO, as pulmonary impedance remains the flow-limiting step.
  • Cyanosis
• Secondary to venous congestion
  • Hepatic congestion and failure
    • Secondary cirrhosis
    • Hepatic carcinoma
  • Protein-losing enteropathy
    
  • Lymphatic failure
    • Ascites
    • Peripheral oedema
    • Venous thrombosis
• Secondary to reduced systemic cardiac output

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References

1. Gewillig M, Brown SC. The Fontan circulation after 45 years: Update in physiology. Heart. 2016;102(14):1081-1086. doi:10.1136/heartjnl-2015-307467