Fontan Physiology
Background
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Fontan is a palliative procedure for patients with functional univentricular physiology
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Selection criteria for performance of Fontan are: adequately sized pulmonary arteries; low PVR; good LV function & the presence of sinus rhythm
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The driving force for blood flow through the pulmonary circulation is the difference between central venous pressure (CVP) & atrial pressure
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There is no active pumping of blood through the lungs
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Cardiac output is essentially completely dependent on pulmonary blood flow
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Therefore, hypovolemia is tolerated very poorly
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Considerations
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Congenital heart disease patient with altered cardiac anatomy & potentially other congenital anomalies
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Hemodymanic & ventilatory goals of Fontan circulation (see below)
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High risk cardiac patient:
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Consider surgery at tertiary cardiac centre
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Consultation with cardiology
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Perioperative TEE invaluable
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Single ventricle pathophysiology:
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Venous congestion: protein loosing enteropathy, kidney disease, hepatic failure, failure to thrive
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Arrhythmias, embolic stroke, anticoagulation
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LV dysfunction
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Hypoxemia & hyperviscosity
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Medication management (possible beta blockers, ACE inhibitors, anticoagulants, diuretics)
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Consideration of bacterial endocarditis prophylaxis if applicable
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Possible ↑ risk of bleeding
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Postoperative monitoring in HAU/ICU
Anesthetic Principles
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Hemodynamic principles:
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Systemic venous pressure: keep full/avoid dehydration
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Pulmonary vascular resistance (PVR) = keep low:
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Avoid hypercarbia, hypoxemia, acidosis, stress, pain, high intra-thoracic pressures
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Cardiac rhythm: strict sinus
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Ventricular function: maintain
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Systemic vascular resistance: maintain
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Fluid management: guided by CVP or TEE (TEE very useful)
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Vascular capacitance is ↑ in the Fontan patient; more fluid may be required than anticipated based on the formula commonly used to calculate fluid requirements.
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Ventilatory strategy:
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Spontaneous ventilation is best as it enhances venous return & pulmonary blood flow
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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.
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↑ bleeding potential: coagulation factor deficiencies, antithrombotic therapy, venous collaterals, & venous hypertension
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Postoperative concerns:
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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
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Adequate analgesia improves pulmonary mechanics & oxygenation; enhanced vigilance is required to avoid the effects of hypercapnia secondary to opioids
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Treat postoperative nausea & vomiting to permit adequate hydration, prevent dehydration & electrolyte loss, & allow the patient to resume their medication regimen
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Pregnancy Considerations
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Case reports exist
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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
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Labor is NOT contraindicated, but needs to occur in a cardiac centre with invasive monitoring (arterial line) & with assisted 2nd stage
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If cearean section: best to use epidural technique
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If GA required, use strategies mentioned above
Laparoscopy Considerations
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Case reports exist
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Detailed discussion with surgeon ahead of time
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Minimize insufflation pressures or do staged insufflation & see effects
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Avoid high intrathoracic pressures, ↓ preload, & hypercarbia
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If cannot tolerate, may need an open technique