Anesthetic Considerations of the Failing Fontan

By Matthew Lilien, MD; Elizabeth Wilson, MD; and Laura Downey, MD
Emory School of Medicine, Children’s Healthcare of Atlanta

Introduction
Congenital heart defects are the most common of birth defects, affecting up to 1% of live births in the United States. Due to major medical and surgical advances over the past three decades, up to 85% of these patients survive into adulthood.1 However, patients born with single ventricle physiology, in which a single ventricle pumps blood to both the systemic and pulmonary vascular beds, have an increased risk for early morbidity and mortality.  The treatment of choice for single ventricle physiology is a staged palliation, in which the final stage is the Fontan operation.2,3 

First described in 1971 by Francois Marie Fontan for the repair of tricuspid atresia, the Fontan operation places the systemic and pulmonary circulations in series, driven by a single anatomical or functional ventricular chamber.4,5 Modifications to the original Fontan operation and improvements in medical management have improved long-term outcomes, but despite “definitive” surgical repair, these patients will never be physiologically normal.  As a result, Fontan patients experience various comorbidities, and many will eventually develop end-stage heart failure, necessitating transplantation.  As patients with Fontan and failing Fontan physiology reach adulthood, their presence in the operating room, labor and delivery room, and intensive care unit is increasingly common. Therefore, an understanding of the Fontan anatomy, physiology, and potential comorbidities is essential to the safe anesthetic management of these patients.

Types of Fontan
Since the first Fontan operation was described in 1971, several modifications have taken place.  The original Fontan connected the atrium directly to the PAs (atrio-pulmonary connection), relying on atrial contraction to create forward flow through the pulmonary system.  Modern techniques include the intracardiac lateral tunnel Fontan (a baffle within the atrium) and the extracardiac Fontan (a conduit outside the atrium).  Often a fenestration is made between the conduit and the atrium to allow for right-to-left shunting (a “pop-off” valve) and adequate cardiac output at the cost of normal saturations, particularly in the immediate post-operative period.2,6

Fontan Physiology
As the Fontan operation places the systemic and pulmonary circulations into series, the single ventricle is responsible for generating enough energy to pump blood through both the systemic and pulmonary vascular beds.7,9 While certain heart defects may be amenable to early Fontan operation, the procedure is typically performed between 1.5-4 years of age, as venous return via the Glenn circuit decreases to 35% by age 4.2,6,7 After completion of the Fontan, patients should have normal oxygen saturations, barring any residual right-to-left shunting. 

In Fontan physiology, the single ventricle preload is dependent on pulmonary blood flow, which in turn is dependent on the gradient across the pulmonary vascular bed from the proximal pulmonary arteries to the common atrium. Therefore, a perfect Fontan circulation would have minimal resistances across the pulmonary vascular bed (no pulmonary artery stenosis or hypoplasia, no pulmonary vein stenosis, low PVR), no atrio-ventricular valve stensosis or regurgitation, good systolic/diastolic function, normal sinus rhythm, and no systemic outflow obstruction. Ideally the pulmonary pressures would be below 15mmHg, the transpulmonary gradient below 7mmHg, and low pulmonary resistance <4 Woods units/m2.3

Fontan Failure

Early Fontan Failure
In the early postoperative period, Fontan failure can be the result of stenotic anastomoses, injury to the conduction system, acute elevations in PVR, or myocardial injury from the insult of surgery and CPB. If these issues are allowed to persist in the immediate post-operative period, decreased PBF and low cardiac output will result.  Fenestrations may temporize periods of low cardiac output at the expense of oxygen saturation.  After identifying the etiology, the appropriate treatment should be taken to treat the problem as quickly as possible: anti-arrhythmics, inotropic support, pulmonary vasodilators, or surgical/cath lab interventions.2,6

Late Fontan Failure
While medical management and improvements in interventional cardiology and surgery have allowed Fontan patients to usually survive well into adulthood, most of these patients will eventually exhibit symptoms of Fontan failure. These patients should have annual follow up appointments with laboratory testing, EKG, CXR, and ECHO.8 Symptoms that should be further evaluated include palpitations, dyspnea, fatigue, diarrhea, and edema or ascites. Over time, patients may develop ventricular failure (single right ventricle earlier than single left ventricle), atrio-ventricular valve dysfunction, elevated pulmonary vascular resistance, arrhythmias, protein losing enteropathy (PLE), plastic bronchitis, and liver disease.  Definitive treatment is heart or combined heart-liver transplantation.3,8

Failing Fontan Etiology

Ventricular Failure
Even in ideal Fontan physiology, cardiac output in these individuals is only 70% of normal patients.9,10,11 The Fontan physiology is a pressure-loaded system. This is secondary to increased systemic vascular tone, decreased venous capacitance, and a baseline PVR greater than a biventricular patient due to a lack of a pulmonary ventricle. Over time, this results in increased strain on the single ventricle that may lead to ventricular dilation and hypertrophy. In addition, after multiple cardiopulmonary bypass surgeries and periods of myocardial ischemia, Fontan patients can develop systolic and/or diastolic ventricular dysfunction.2 Ventricular failure in Fontan patients is often resistant to standard medical management, but includes afterload reduction with ACE inhibitors, diuretics, and inotropic support.2,3,12

Elevated PVR
Ideally, the transpulmonary gradient (TPG) (the systemic venous pressure minus the common atrial pressure) in Fontan circulation is between 10-15mmHg.8 Therefore, anything that increases the TPG will eventually result in Fontan failure. The most common causes of elevated TPG include pulmonary artery/vein stenosis, pulmonary emboli, elevated PVR, or AV valve failure. While the etiology of increased PVR in Fontan patients is not clear, it has been postulated that Fontan patients have dysfunctional nitric oxide synthesis.  Therefore, first line treatment for elevated PVR is often phosphodiesterase type 5 inhibitor.  If a mechanical obstruction exists, patients may go to the cardiac cath lab for balloon dilation or stenting of stenotic arteries or veins. A more invasive option would be surgical reconstruction of the Fontan circulation or AV valve repair.  In most Fontan patients, the fenestration will close spontaneously.  However, patients with elevated PVR may continue to use their fenestration to maintain cardiac output. In patients whose fenestration has closed, creation of a fenestration may improve cardiac output in failing Fontan circulation.2,3 

Long-term Sequelae of Fontan Circulation

Arrhythmias
The incidence of arrhythmias in Fontan patients is approximately 20% at 10 years and 50% at 20 years.3 Risk factors for arrhythmias include atrial suture lines, atrial dilation (particularly in patients with the atriopulmonary connection) and ventricular failure. Atrial arrhythmias, including intra-atrial re-entry tachycardia and atrial flutter, are more common, while ventricular arrhythmias are usually associated with poor ventricular function. Since arrhythmias are often associated with hemodynamic compromise, they should be aggressively treated with pharmacologic therapy, catheter ablation, pacemaker placement or the MAZE procedure.3,4,12

Thromboembolic Events
Thrombotic events occur in 2-33% of patients following Fontan operations and can be life threatening. Risk factors for thrombus formation include right atrial dilatation, reduced cardiac output, anatomic obstructions in the Fontan circuit, and arrhythmias. Management includes anticoagulation, maintaining sinus rhythm, and correcting any obstruction to the Fontan circulation. Occasionally surgical thrombectomy or Fontan revision is needed.3,4

Protein Losing Enteropathy
Protein losing enteropathies is a poorly understood condition that is expected to affect between 3-15% of Fontan patients.2 It is defined as persistent hypoalbuminemia (<3.0mg/dL) in the absence of liver or renal disease. Clinical features include abdominal pain, diarrhea, edema and ascites. Patient with PLE have significantly elevated systemic venous pressures, decreased cardiac index, and increased end-diastolic ventricular pressure. The current theory is that PLE is caused by decreased cardiac output, which leads to increased mesenteric vascular pressures, inflammation, lymphatic hypertension, and enterocyte membrane dysfunction.  The protein loss results in interstitial and peripheral edema, ascites, pleural and pericardial effusions.  Over time these patients are more prone to infection and thromboembolic events. The development of PLE is a poor prognostic sign, with mortality approximately 50% within five years after the diagnosis is made.  PLE is an indication for heart transplant.2,3,4

Plastic bronchitis
After Fontan procedure, approximately 1-4% of patients develop plastic bronchitis, in which proteinaceous material forms casts in the airways causing partial or complete obstruction of the tracheobronchial tree.  Patients often present with asthma like symptoms or more acutely with dyspnea and desaturation.  Treatments include bronchodilators, steroids, inhaled hypertonic saline, mucolytics, antibiotics, and possible rigid bronchoscopy to remove casts. Like PLE, patients diagnosed with plastic bronchitis have a 50% mortality within five years, and definitive treatment is heart transplant.2,3,6

Kidney Dysfunction
Low cardiac output and venous congestion in Fontan patients can cause kidney dysfunction, reduced glomerular filtration, and elevated creatinine. Signs of renal failure found on follow up warrant consultation with a nephrologist familiar with the Fontan circulation.3

Liver Dysfunction
The cause of liver dysfunction is a low cardiac output state combined with increased hepatic congestion secondary to elevated systemic venous pressure, all causing decreased venous and arterial blood supply to the liver. Liver dysfunction is often found on routine blood work with elevated liver enzymes or on routine ultrasound, MRI, or CT. No specific surveillance method exists but some physicians recommend imaging every three to five years beginning five years after the operation, unless symptoms warrant earlier surveillance.2,3,13

Anesthetic considerations for Failing Fontan patients
The main challenges anesthesiologists face in caring for patients with failing Fontan are poor systolic function, elevated Fontan and RV diastolic pressures, and atrial arrhythmias. For patients coming for elective surgery, access to ECHO reports assessing ventricular function, AV valve function, patency of Fontan pathway, and fenestration status will be helpful.8 Depending on the procedure, a cardiac catheterization to assess hemodynamics may be necessary if there has been clinical deterioration.  The goals of intraoperative management include maintenance of sinus rhythm, ventricular contractility, and adequate preload to enhance PBF and cardiac output, while minimizing PVR and afterload increases. However, given the in-series circulation, it must be understood that increasing preload will also directly increase afterload, and so a delicate balance must be struck.

General anesthesia, regional anesthesia or sedation can all be safely achieved. Many of these patients will require premedication to alleviate anxiety and facilitate IV placement. For patients with well-compensated Fontan physiology, a mask induction can be performed safely.  However, patients with marginal physiology will benefit from a controlled IV induction with medications that do not cause myocardial depression.5,6 In some instances, it may be necessary to start inotropic support to counteract the vasodilatory and myocardial depressant effects of anesthetic agents. Dehydration should be avoided and patients may require volume replacement prior to induction to replace the preoperative fluid deficit.5,8 

Intraoperatively, ventilation strategies should be aimed at maintaining low PVR through good oxygenation, avoiding hypo/hyperventilation, and minimizing mean airway pressures.  During positive pressure ventilation, moderately elevated tidal volumes, low respiratory rates, longer expiratory time, and minimal PEEP should be used.9  Depending on the procedure, invasive monitoring such as an arterial line, a central venous line to measure Fontan pressures or deliver inotropic support, and TEE may be necessary.  Additionally, Fontan patients are often anticoagulated and may have increased risk of bleeding intraoperatively. Good pain control intraoperatively and postoperatively will decrease catecholamine release and promote adequate breathing to prevent increases in PVR associated with splinting and hypercarbia.  Neuraxial techniques should be used with caution in patients who have been anticoagulated.

Conclusion
Although surgical and medical advancements for single ventricle patients has improved over the past three decades, many of these patients will eventually develop end-stage heart failure and other complications from long-standing Fontan physiology. Therefore, it is important for anesthesiologists to have an understanding of this complex anatomy and physiology to safely manage these patients in the operating room, labor and delivery suites, and intensive care units.

References

  1. Tabarsi, Nazlee, et al. “Meta-Analysis of the Effectiveness of Heart Transplantation in Patients With a Failing Fontan.” The American Journal of Cardiology, vol. 119, no. 8, 2017, pp. 1269–1274., doi:10.1016/j.amjcard.2017.01.001.
  2. Davies, Ryan R., et al. “The Fontan Procedure: Evolution in Technique; Attendant Imperfections and Transplantation for âœFailureâ.” Seminars in Thoracic and Cardiovascular Surgery: Pediatric Cardiac Surgery Annual, vol. 14, no. 1, 2011, pp. 55–66., doi:10.1053/j.pcsu.2011.01.014.
  3. Management of Patients Post-Fontan Procedure, www.uptodate.com/contents/management-of-patients-post-fontan-procedure.
  4. Vaughn, Gabrielle, et al. “Management of the Failing Fontan: Medical, Interventional and Surgical Treatment.” Progress in Pediatric Cardiology, vol. 43, 2016, pp. 51–56., doi:10.1016/j.ppedcard.2016.07.007.
  5. Walker. “Perioperative Management of a Patient With Fontan Physiology for Posterior Spinal Fusion.” Journal of Medical Cases, 2014, doi:10.14740/jmc1789w.
  6. Andropoulos, Dean B., et al. Anesthesia for Congenital Heart Disease. Wiley, 2015.
  7. Nasr, V.G., & DiNardo, J.A. (2017). The Pediatric cardiac anesthesia handbook, Hoboken, NJ: John Wiley & Sons Ltd.
  8. Pitkin, Andrew D., et al. “Perioperative Management of a Patient With Failed Fontan Physiology.” Seminars in Cardiothoracic and Vascular Anesthesia, vol. 17, no. 1, 2013, pp. 61–65., doi:10.1177/1089253213476556
  9. Jolley, Matthew, et al. “Fontan Physiology Revisited.” Anesthesia & Analgesia, vol. 121, no. 1, 2015, pp. 172–182., doi:10.1213/ane.0000000000000717.
  10. Gerche, Andre La, and Marc Gewillig. “What Limits Cardiac Performance during Exercise in Normal Subjects and in Healthy Fontan Patients?” International Journal of Pediatrics, vol. 2010, 2010, pp. 1–8., doi:10.1155/2010/791291.
  11. Cote, Charles J., et al. A Practice of Anesthesia for Infants and Children. Elsevier, 2019.
  12. Michielon, Guido, et al. “Orthotopic Heart Transplantation in Patients with Univentricular Physiology.” Current Cardiology Reviews, vol. 7, no. 2, Jan. 2011, pp. 85–91., doi:10.2174/157340311797484259.
  13. Berg, Christopher J., et al. “Mortality Risk Stratification in Fontan Patients Who Underwent Heart Transplantation.” The American Journal of Cardiology, vol. 119, no. 10, 2017, pp. 1675–1679., doi:10.1016/j.amjcard.2017.02.005.
  14. John, Anitha S. “Fontan Repair of Single Ventricle Physiology.” Cardiology Clinics, vol. 33, no. 4, 2015, pp. 559–569., doi:10.1016/j.ccl.2015.07.010.

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