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 no active pumping of blood through the lungs

    • Cardiac output is essentially completely dependent on pulmonary blood flow

    • Therefore, hypovolemia is tolerated very poorly

 

 

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 loosing enteropathy, kidney disease, hepatic failure, failure to thrive 

    • Arrhythmias, embolic stroke, anticoagulation

    • LV dysfunction

    • Hypoxemia & hyperviscosity

  • Medication management (possible beta blockers, ACE inhibitors, anticoagulants, diuretics) 

  • Consideration of bacterial endocarditis prophylaxis if applicable 

  • Possible ↑ risk of bleeding 

  • Postoperative monitoring in HAU/ICU 

 

 

Anesthetic Principles 

 

  • Hemodynamic principles:

    • Systemic venous pressure: keep full/avoid dehydration  

    • Pulmonary vascular resistance (PVR) = keep low:

      • Avoid hypercarbia, hypoxemia, acidosis, stress, pain, high intra-thoracic pressures 

    • Cardiac rhythm: strict sinus

    • Ventricular function: maintain 

    • Systemic vascular resistance: maintain 

  • 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 requirements.

  • 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 PEEP, moderately elevated tidal volumes (10–15 mL/kg), ensure adequate intravascular volume.

  • ↑ bleeding potential: coagulation factor deficiencies, antithrombotic therapy, venous collaterals, & venous hypertension

  • 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 IV 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 ↓ 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 cearean section: best to use epidural technique 

  • If GA required, use strategies mentioned above 

 

 

Laparoscopy Considerations 

 

  • Case reports exist 

  • Detailed discussion with surgeon ahead of time 

  • Minimize insufflation pressures or do staged insufflation & see effects

  • Avoid high intrathoracic pressures, ↓ preload, & hypercarbia 

  • If cannot tolerate, may need an open technique