Fontan Physiology

 

 

Background

 

  • Fontan is a palliative procedure for patients with functional univentricular physiology

  • Selection criteria for performance of Fontan are: adequately sized pulmonary arteries; low PVR; good LV function & the presence of sinus rhythm

  • The driving force for blood flow through the pulmonary circulation is the difference between central venous pressure (CVP) & atrial pressure: 

    • There is NOT active pumping of blood through the lungs  

    • Cardiac output is essentially completely dependent on pulmonary blood flow

    • Hypovolemia is tolerated very poorly

  • Preoperative preparation:

    • Review information from patient’s cardiologist; changes in patient’s exercise tolerance, level of cardiac impairment, details of the patient’s physiology, anatomy, & any residual & sequelae of previous surgeries

    • Minimize NPO interval, maintain intravascular volume (↓ preload results in ↓ pulmonary blood flow & cardiac output)

 

 

Key Considerations

 

  • Congenital heart disease patient with altered cardiac anatomy & potentially other congenital anomalies 

  • Hemodymanic & ventilatory goals of Fontan circulation (see below) 

  • High risk cardiac patient 

  • Consider surgery at tertiary cardiac centre 

  • Consultation with cardiology 

  • Perioperative TEE invaluable 

  • Single ventricle pathophysiology

    • Venous congestion: protein losing enteropathy, CKD, hepatic failure, FTT

    • Arrhythmias, embolic stroke, anticoagulation

    • LV dysfunction

    • Hypoxemia & hyperviscosity

  • Medication management (possible beta blockers, ACEI, anticoagulants, diuretics) 

  • Consideration of bacterial endocarditis prophylaxis if applicable 

  • Possible ↑ risk of bleeding 

  • Postoperative monitoring in HAU/ICU 

 

 

Goals

 

  • Hemodynamic goals: 

    • Preload: keep full, avoid dehydration

    • Rate & rhythm: strict normal sinus rhythm

    • Contractility: maintain

    • Afterload: maintain

    • Pulmonary vascular resistance: keep low

      • Avoid hypercarbia, hypoxemia, acidosis, stress, pain, high intrathoracic pressures 

  • Fluid management:

    • Guided by CVP or TEE (TEE very useful)  

    • Vascular capacitance is ↑ in the Fontan patient; more fluid may be required than anticipated based on the formula commonly used to calculate fluid requirement

  • Ventilatory strategy:

    • Spontaneous ventilation is best as it enhances venous return & pulmonary blood flow 

    • For PPV:  

      • Limit peak inspiratory pressure (<20 cmH2O), use low respiratory rates (<20 bpm), short inspiratory times, avoid excessive positive end-expiratory pressure, moderately elevated tidal volumes (10–15 mL/kg), ensure adequate intravascular volume

  • Postoperative concerns:

    • Maintaining volume status, acid-base balance, & cardiac output are essential in the postoperative period; ensure adequate hydration & aggressively manage low cardiac output with intravenous hydration & inotropes

    • Adequate analgesia improves pulmonary mechanics & oxygenation; enhanced vigilance is required to avoid the effects of hypercapnia secondary to opioids

    • Treat postoperative nausea & vomiting to permit adequate hydration, prevent dehydration & electrolyte loss, & allow the patient to resume their medication regimen

 

 

Pregnancy Considerations

 

  • Case reports exist 

  • Titrated epidural is probably the safest technique as it does not worsen PVR; caution with reduction in preload so ensure well-hydrated; reduction in afterload is probably desirable

  • Labor is NOT contraindicated but needs to occur in a cardiac centre with invasive monitoring (arterial line) & with assisted 2nd stage

  • If cesarean section: best to use epidural technique 

  • If GA required, use strategies mentioned above 

 

 

Laparoscopy & Fontan

 

  • Case reports exist 

  • Detailed discussion with surgeon ahead of time 

  • Minimize insufflation pressures or do staged insufflation & see effects

  • Avoid high intrathoracic pressures, reduced preload, & hypercarbia 

  • If cannot tolerate, may need an open technique 

Further Reading 

Miller's Anesthesia, Chapter 78, 

 

 

 

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