Fontan Circulation

Preload is the driving pressure - There is no pump between the systemic veins and the lungs. Filling pressure is the only thing pushing blood through the pulmonary bed, so hypovolemia does not merely reduce output — it stalls the circuit. Fontan patients tolerate and need central venous pressures of 15 to 20 mm Hg, so a number that would alarm you in anyone else is the target here.

Minimize the fasting window - Dehydration is what breaks a passive circulation. Shorten the NPO period and start IV fluids while they wait rather than letting them arrive dry.

Positive pressure ventilation is the enemy - Raising intrathoracic pressure narrows the gradient for venous return, cuts pulmonary blood flow, and drops cardiac output. Keep spontaneous ventilation wherever the case allows it, since negative-pressure inspiration actually augments systemic venous return — provided you do not let them go hypercarbic.

If you must ventilate, ventilate flat - Low respiratory rates, short inspiratory times, low PEEP and tidal volumes of 5 to 6 mL/kg give adequate pulmonary blood flow at normocarbia. Enough PEEP to hold FRC earns its place: it preserves PaO2, prevents atelectasis, and avoids hypoxic pulmonary vasoconstriction. Hyperventilation backfires — the respiratory alkalosis does not offset the higher mean intrathoracic pressure, and pulmonary blood flow falls.

Guard PVR relentlessly - Pain, hypercarbia, acidosis, vasoactive agents and rising intrathoracic pressure are the common perioperative causes of a PVR spike. Inhaled nitric oxide lowers PVR without dropping systemic pressure and counters hypoxemia-induced pulmonary vasoconstriction.

Sinus rhythm is not optional - The single ventricle depends on atrial contraction for filling, and arrhythmias are common because the right atrium was manipulated at the original surgery. Losing the atrial kick cuts venous return, pulmonary blood flow and ventricular filling time at once. Preload reserve and contractility are both limited, so output rides on heart rate — treat bradycardia and treat lost rhythm early.

Central lines: think twice - Thrombus, air embolus, infection and impaired venous return usually outweigh what a CVP number buys you, and central access is not recommended unless the case truly requires it. Keep a low threshold for an arterial line instead; arterial waveform-based continuous cardiac output monitoring has been used successfully in this population and gives early warning of hypervolemia, hypovolemia and decompensation.

Monitor limb by limb - The surgically rerouted circulation means saturation and pressure can differ between extremities. Check each individually rather than assuming one arm speaks for the whole patient.

Chronic hypoxia drives polycythemia - Hematocrit and hemoglobin run high because oxygen-carrying capacity is doing compensatory work. Do not read a "normal" hemoglobin as reassuring, and agree the transfusion trigger with the cardiac team rather than applying a general threshold.

Stage the failing Fontan - Check an albumin, LFTs, coagulation studies and platelet count. Protein-losing enteropathy and plastic bronchitis occur in up to 5% and carry up to 50% mortality within 5 years of diagnosis. Chronically elevated central venous pressure produces liver fibrosis, cirrhosis and hepatocellular carcinoma. In a large long-term cohort, cardiac reoperation (32%), arrhythmia treatment (32%), thrombosis (12%) and protein-losing enteropathy (9%) were the most common complications.

Thromboembolism is a standing risk - Up to 25% of thromboembolic events in Fontan patients are fatal. Many are on warfarin or aspirin, though there is no consensus regimen or duration after Fontan. Confirm the agent and last dose, and take any neuraxial timing from the current ASRA anticoagulation guidelines alongside the cardiology plan — not from memory.

Debubble obsessively - Fenestrated Fontans and residual atrial communications give air a direct route to the systemic side. Purge lines, use filters, and treat every injection as a potential paradoxical embolus.

Regional works when it is titrated - Epidural anesthesia has been used successfully for cesarean delivery after Fontan repair, with preload optimized in advance and the catheter dosed incrementally in 3 to 5 mL boluses over roughly 30 minutes to a T4 level. A sudden sympathectomy is what these patients cannot absorb.

Functional status predicts trouble - Lower-than-expected exercise capacity and some degree of ventricular dysfunction are near-universal by adolescence, and poor functional status and low exercise performance predict death or transplant. Ask what they can actually do, and get the most recent echo and right heart catheterization numbers.

Plan analgesia before emergence - Pain raises PVR, which cuts pulmonary blood flow and output. Have the multimodal and regional plan in place before you wake them, and arrange a monitored bed.

The Fontan is the final-stage palliation for a functionally single ventricle — hypoplastic left heart syndrome accounts for most cases (25% to 67%), along with tricuspid atresia, pulmonary atresia and other single-ventricle defects. Systemic venous return is anastomosed directly to the pulmonary arteries as a total cavopulmonary connection, so deoxygenated blood bypasses the heart entirely and the one working ventricle spends all its energy on systemic flow.

The price is that there is no pulmonary ventricle. Pulmonary blood flow is passive, driven by central venous pressure alone, which makes cardiac output exquisitely sensitive to intrathoracic pressure and to pulmonary vascular resistance (PVR). The circuit only works if the ventricle is functional, PVR is low, and nothing obstructs the pathway. Over decades it drifts toward failure — falling preload, rising systemic venous pressure, chronically low output. Some 50,000 to 70,000 people worldwide live with a Fontan, and most now reach adulthood.