Fontan Physiology Anesthesia: Essential Guidelines for Optimal Management5 min read

Providing safe and effective anesthesia for patients with Fontan physiology can be challenging due to their unique cardiovascular anatomy and hemodynamics. This article presents a comprehensive clinical protocol for anesthesiologists managing these complex cases, covering key physiological considerations, monitoring requirements, and perioperative strategies to optimize outcomes. By understanding the underlying principles of single ventricle physiology and the impact of cardiac shunts, you’ll be well-equipped to deliver high-quality care tailored to the specific needs of Fontan patients.

Understanding Fontan Physiology

Fontan circulation is a surgically created pathway that directs systemic venous return directly to the pulmonary arteries, bypassing the subpulmonary ventricle. This unique physiology results in several key considerations for anesthesia management:

• Passive pulmonary blood flow dependent on venous pressure
• Increased systemic venous pressure and reduced cardiac output
• Altered pulmonary vascular resistance and ventilation-perfusion mismatch
• Potential for paradoxical emboli and thrombotic complications

Thorough understanding of these physiological alterations is essential for tailoring anesthetic techniques and optimizing hemodynamic management in Fontan patients.

Single Ventricle Anatomy and Function

In Fontan circulation, a single functional ventricle supports both systemic and pulmonary circulations. This ventricle is often hypertrophied and may have diastolic dysfunction, leading to preload sensitivity and reduced cardiac reserve. Anesthesiologists must carefully titrate fluids and inotropes to maintain adequate preload without causing ventricular distension or failure.

Pulmonary Vascular Resistance and Oxygenation

Pulmonary blood flow in Fontan patients is passive and driven by the pressure gradient between central venous pressure (CVP) and left atrial pressure. Elevations in pulmonary vascular resistance (PVR) can significantly impair pulmonary perfusion and oxygenation. Strategies to minimize PVR include:

• Maintaining normocapnia and avoiding hypoxia
• Judicious use of positive end-expiratory pressure (PEEP)
• Preventing hypothermia and pain-induced sympathetic stimulation
• Selective pulmonary vasodilators in refractory cases

Perioperative Monitoring and Management

Comprehensive monitoring is crucial for detecting and promptly treating derangements in Fontan physiology during anesthesia. Key components of the monitoring protocol include:

Invasive Hemodynamic Monitoring

• Arterial line for continuous blood pressure monitoring
• Central venous catheter for CVP trends and venous access
• Consider pulmonary artery catheter or transesophageal echocardiography for complex cases

Goal-directed therapy targeting CVP of 10-15 mmHg and mean arterial pressure (MAP) >50 mmHg can help maintain adequate cardiac output and tissue perfusion.

Oxygenation and Ventilation Monitoring

• Continuous pulse oximetry and capnography
• Arterial blood gas analysis for pH, PaO2, and PaCO2
• Maintain PaO2 >60 mmHg and PaCO2 35-45 mmHg
• Use lung-protective ventilation strategies with low tidal volumes and moderate PEEP

Careful attention to oxygenation and ventilation parameters is essential to prevent hypoxemia, acidosis, or pulmonary hypertensive crises.

Coagulation and Thrombosis Prophylaxis

Fontan patients are at increased risk for both bleeding and thrombotic complications due to altered hemostasis and venous stasis. Perioperative management should include:

• Baseline and perioperative coagulation studies (PT, aPTT, fibrinogen)
• Consideration of viscoelastic testing (TEG or ROTEM) for complex cases
• Antifibrinolytic therapy with tranexamic acid or aminocaproic acid
• Mechanical and pharmacologic thromboprophylaxis (sequential compression devices, heparin) when appropriate

Balancing the risks of bleeding and thrombosis requires individualized assessment and multidisciplinary collaboration with the surgical and hematology teams.

Anesthetic Techniques and Considerations

The choice of anesthetic technique for Fontan patients should prioritize maintaining hemodynamic stability, minimizing PVR, and preserving oxygenation. Some key considerations include:

Induction and Maintenance Agents

• Prefer intravenous induction with ketamine, etomidate, or careful titration of propofol
• Avoid agents that cause significant vasodilation or myocardial depression (e.g., high-dose propofol, thiopental)
• Maintain anesthesia with balanced technique using low-dose volatile agent and short-acting opioid
• Consider total intravenous anesthesia (TIVA) for cases requiring neurologic monitoring

Fluid Management and Hemodynamic Support

• Maintain euvolemia with goal-directed fluid therapy targeting CVP 10-15 mmHg
• Use balanced crystalloids and colloids judiciously to avoid fluid overload
• Consider inotropic support with milrinone, dobutamine, or epinephrine for depressed cardiac function
• Avoid pure vasopressors (e.g., phenylephrine) that may increase PVR
• Use vasopressin cautiously for refractory hypotension

Pulmonary Hypertension and Hypoxemia Management

In cases of pulmonary hypertensive crises or refractory hypoxemia, consider the following strategies:

• Inhaled nitric oxide (iNO) for selective pulmonary vasodilation
• Inhaled or intravenous prostacyclin analogs (epoprostenol, iloprost)
• Oral or intravenous phosphodiesterase inhibitors (sildenafil, milrinone)
• Extracorporeal membrane oxygenation (ECMO) for severe, refractory cases

Prompt recognition and aggressive treatment of pulmonary hypertension is critical to prevent circulatory collapse and end-organ dysfunction in Fontan patients.

Postoperative Care and Outcomes

Fontan patients require close monitoring and supportive care in the postoperative period to optimize recovery and prevent complications. Key aspects of postoperative management include:

Intensive Care Unit (ICU) Management

• Continued invasive monitoring and goal-directed therapy
• Careful titration of inotropes and vasodilators
• Aggressive pulmonary toilet and early extubation when feasible
• Strict fluid balance and early initiation of diuresis
• Prophylaxis for thrombosis and gastrointestinal bleeding

Pain Management and Sedation

Adequate pain control is essential to minimize sympathetic stimulation and prevent pulmonary hypertensive crises. A multimodal approach incorporating regional anesthesia, acetaminophen, and low-dose opioids can help optimize analgesia while minimizing side effects. Sedation should be used judiciously to prevent respiratory depression and maintain a low-normal PaCO2.

Long-Term Outcomes and Follow-Up

Despite advances in surgical techniques and perioperative care, Fontan patients remain at risk for long-term complications such as arrhythmias, thromboembolism, liver dysfunction, and protein-losing enteropathy. Regular follow-up with a multidisciplinary team, including cardiologists, electrophysiologists, and hepatologists, is essential for early detection and management of these complications.

Frequently Asked Questions

What is the optimal mean arterial pressure (MAP) for Fontan patients during anesthesia?

Maintaining a MAP >50 mmHg is generally recommended to ensure adequate perfusion pressure for vital organs. However, the specific target may vary based on individual patient factors such as ventricular function, aortic arch anatomy, and baseline blood pressure. Close communication with the surgical team and use of invasive monitoring can help guide individualized MAP goals.

How can anesthesiologists minimize the risk of paradoxical emboli in Fontan patients?

Fontan patients are at increased risk for paradoxical emboli due to the presence of residual intracardiac shunts or collateral vessels. Strategies to minimize this risk include:

• Meticulous de-airing of intravenous lines and infusions
• Use of air filters on all venous access ports
• Avoidance of nitrous oxide, which can expand air emboli
• Transesophageal echocardiography to detect and guide treatment of emboli
• Consideration of preoperative anticoagulation or inferior vena cava filters in high-risk cases

What are the indications for extracorporeal membrane oxygenation (ECMO) in Fontan patients?

ECMO may be indicated for Fontan patients with severe, refractory hypoxemia or hemodynamic instability despite maximal medical therapy. Specific indications include:

• Cardiac arrest or severe ventricular dysfunction
• Pulmonary hypertensive crisis unresponsive to pulmonary vasodilators
• Severe hypoxemia (PaO2 <40 mmHg) despite optimal ventilation and oxygenation strategies
• Persistent lactic acidosis or end-organ dysfunction despite adequate circulatory support

The decision to initiate ECMO should be made in consultation with the multidisciplinary team, including cardiac surgeons, intensivists, and perfusionists, based on individual patient factors and institutional capabilities.

Conclusion

Providing safe and effective anesthesia for patients with Fontan physiology requires a thorough understanding of their unique cardiovascular anatomy, hemodynamic alterations, and potential complications. By adhering to a comprehensive clinical protocol that emphasizes meticulous monitoring, maintenance of hemodynamic stability, and prevention of pulmonary hypertensive crises, anesthesiologists can optimize outcomes for these complex patients.

Key strategies include goal-directed fluid therapy, judicious use of inotropes and pulmonary vasodilators, lung-protective ventilation, and proactive management of bleeding and thrombotic risks. Close collaboration with the multidisciplinary team, including surgeons, intensivists, and hematologists, is essential for navigating the perioperative challenges and ensuring the best possible long-term outcomes for Fontan patients.

By staying up-to-date with the latest evidence-based practices and adapting to the individual needs of each patient, anesthesiologists can play a critical role in the successful management of this unique and challenging patient population. With careful planning, vigilant monitoring, and a commitment to ongoing education and improvement, we can continue to push the boundaries of what is possible in the care of Fontan patients undergoing anesthesia.

MedicalHubNews PHD Team

The Health Insight Team consists of dedicated students and PhD candidates from leading medical schools around the world. Collaborating with experienced medical professionals, our team provides well-researched, evidence-based information on a wide range of health topics, including prescription medications, surgical procedures, anesthesia, and nutritional health. The articles by MedicalHubNews PHD Team are for educational purposes only. For medical issues, consult your doctor or healthcare provider.