Fontan Circulation

A fully complete Fontan circulation necessitates surgery to create a direct connection between the venous return and the PA, excluding the subpulmonary ventricle. Blood flow through the lungs is passive and depends on a relatively high CVP, low PVR and low systemic atrial and ventricular diastolic pressures. Patients are delicately balanced between an inadequate blood supply to the lungs, causing cyanosis, and an excessive pulmonary blood flow (PBF) causing pulmonary oedema. Over time, these patients develop chronically increased venous pressure, leading to hepatic congestion, pulmonary venous congestion, an increased PAP and, eventually, cardiac failure.

Pulmonary Hypertension

PHT, defined as a mean PAP above 25 mmHg at rest, is a major perioperative risk factor. Strategies to manage PHT include avoidance of triggering agents, minimizing increases in the PVR with good oxygenation, avoidance of acidosis and limiting peak ventilatory pressures. Some patients are already taking conventional medications such as β-blockers, diuretics, digoxin or ACE inhibitors and may also require specific pulmonary vasodilators such as inhaled NO, prostacyclin (e.g. iloprost), calcium channel antagonists (e.g. diltiazem), phosphodiesterase-5 inhibitors (e.g. oral/IV sildenafil) or endothelin receptor antagonists (e.g. bosentan). Anaesthetic management must be tailored to the underlying cause of PHT in the ACHD patient.

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   1. Systemic-to-pulmonary shunt with an increased PVR or primary PHT – this may respond to pulmonary vasodilators.

   
   
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   2. Eisenmenger syndrome – Long-standing systemic-to-pulmonary shunts, leading to systemic pulmonary pressures, reversal of the right-to-left shunt and cyanosis. This is an anaesthetic challenge as both PHT and an exacerbation of the cyanosis must be addressed. This may respond to oral pulmonary vasodilators. The RV is accustomed to high afterload.

   
   
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   3. PHT due to left heart disease – this may require inotropic support and systemic afterload reduction.

Unrestricted Shunts

Patients with ASDs, VSDs, aortopulmonary collaterals or surgically created systemic-to-pulmonary shunts (e.g. Blalock–Taussig (B–T), Waterston and Potts) may have pulmonary to systemic blood flow (Q_P:Q_S) of 2:1 or 3:1 in room air, at rest. Breathing 100% oxygen reduces the PVR, leading to increased Q_P:Q_S, results in reduced systemic oxygen delivery and metabolic acidosis. Patients with single ventricles and pulmonary circulation supplied by aortopulmonary collaterals have a precarious balance between PBF and systemic oxygen delivery. Ideally, these patients should be maintained on an inspired oxygen concentration that recreates their normal room air oxygen saturations at rest, with the minimum ventilator settings, to maintain a normal PaCO₂.

History

Details of the original congenital lesion, previous percutaneous or open surgical interventions, anaesthetic records and subsequent cardiological investigations should be reviewed. It is important to understand the patient’s current anatomy, any residual structural defects and the extent of any physiological adaptation. Many patients are accustomed to poor exercise tolerance, so it is important to determine what is normal for them. A history of prolonged periods of ventilation or prior tracheostomy should be elicited, as well as details of any associated pulmonary disease.

Episodes of syncope, chest pain, cyanosis or arrhythmias should be noted.

Cyanotic patients are at risk of thrombosis and details of anticoagulation therapy should be obtained. Patients may be taking other medications such as β-blockers and ACE inhibitors – details of these should be sought.

CHD is associated with a number of genetic syndromes, such as Trisomy 21 and 22q11 deletion – relevant associated features should also be elicited.

Physical Examination

The presence of clubbing, cyanosis and signs of congestive heart failure (jugular venous distension, pulmonary crackles, hepatomegaly and peripheral oedema) should be sought.

Problems associated with the airway should be highlighted as these can substantially increase the risk, especially in the setting of cyanotic heart disease or PHT. Previous cardiac surgery may have resulted in damage to the vocal cords, recurrent laryngeal nerve or phrenic nerve palsy, or Horner syndrome. Prolonged postoperative mechanical ventilation of the lungs may have led to subglottic stenosis.

Peripheral pulses may be diminished, unequal or absent following surgery or previous shunt placement. The presence of additional or abnormal heart sounds are evidence of residual disease.

Neurological assessment may reveal developmental delay and learning difficulties. This may be due to associated congenital disorders, chronic hypoxaemia or following complex cardiac surgery, with long bypass or deep hypothermic circulatory arrest times or prolonged intensive care. Cerebrovascular events occur in up to 14% of patients with cyanotic heart disease, especially in the presence of AF and hypertension.