Fontan circulation

Definition: separates pulmonary and systemic blood flow in single ventricle physiology; accomplished by intra-atrial lateral tunnelling of the IVC flow into RPA, or extracardiac via conduit (extracardiac Fontan)

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Physiology:

• Better systemic oxygenation
• Reduced volume load to the systemic ventricle
• May be fenestrated to obtain adequate CO postoperative

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Preoperative preparation:

ECG, CXR, CUS, FBE, clotting, UECs, PRBC (4), FFP (2), platelets (2), cryoprecipitate (2).

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Risk assessment for Fontan candidates:

• Elevated PVR (>4 Wood units or mPAP >15 mmHg)
• Impaired ventricular function (EF <45%)
• Impaired ventricular diastolic function
• AV valve incompetence (LVEDP >12 mmhg)
• Small PA size (McGoon ratio)
• Subaortic obstruction

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Postoperative management:

Discuss anticoagulation with surgeon…

• Commence heparin 10 U/kg/hr once no major bleeding , further long-term anticoagulation with Vitamin-K antagonist (INR 2-3)
• Respiratory: normoxaemia, in fenestrated Fontan SpO2 >80%, normocapnea (mild hypercapnea improves oxygenation!), try to extubate early if feasible
• Inotropes: usually not required, if so milrinone to decrease PVR and SVR and improve ventricular dysfunction
• Goal is to lower PVR if possible, as this is the main determinant factor for CO in postoperative Fontan circulation; extubate early
• Fluid restriction: 2 ml/kg/hr for the first day; feed early
• Haemostasis (restrictive transfusion strategy if stable)

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Specific problems:

• Pleural effusions → replace losses (full/half/quarter)
• Low CO: hypovolemia (low CVP, low LAP) → volume
• Obstruction SVC/PA anastomosis (high CVP, low LAP) → ECHO, angio
• High PVR (high CVP, low LAP). To lower PVR: milrinone, iNO
  
• Exclude pulmonary venous obstruction (ECHO)
• Ventricular dysfunction (high CVP, high LAP): commence low dose milrinone (0.25 mcg/kg/min) as more common diastolic dysfunction, exclude AV valve regurgitation (ECHO)
• Persistent hypoxaemia: fenestration, low CO → ECHO; low SmvO2, unrecognised abnormal systemic connection → ECHO, angio, lung disease
• Systemic venous hypertension: pleural effusion, ascites – drain early. If chronic: protein-losing enteropathy
• Dysrhythmias: avoid inotropic, chronotropic support if feasible

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Outcome:

• Low perioperative mortality <2%
• Absence of death or transplantation after 1y: 80%, 5 yrs: 77%, 10 yrs: 75%, 25 yrs: 54%
• Major morbidity: tacharrhythmias, thrombotic events, PLE

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References:

[1] Critical Heart Disease in Infants and Children; 2nd ed, Nichols et al: Tricuspid Atresia

[2] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S57-69: Giglia et al: Preoperative pulmonary hemodynamics and assessment of operability: is there a pulmonary vascular resistance that precludes cardiac operation?

[3] Interact Cardiovasc Thorac Surg. 2010 Mar;10(3):428-33: Gewillig et al: The Fontan circulation: who controls cardiac output?

[4] Interact Cardiovasc Thorac Surg. 2010 Feb;10(2):262-5. Gewillig et al: Volume load paradox while preparing for the Fontan: not too much for the ventricle, not too little for the lungs

[5] Pediatr Cardiol. 2007 Nov-Dec;28(6):448-56: Deal t al: Arrhythmia management in the Fontan patient.[6] Circulation. 2008 Jan 1;117(1):85-92: Khairy et al: Long-term survival, modes of death, and predictors of mortality in patients with Fontan surgery

[7] Pediatr Crit Care Med. 2011 Vol. 12, No.1: 39-45: Cholette et al: Children with single-ventricle physiology do not benefit from higher haemoglobin levels post cavopulmonary connection: Results of a prospective, randomized, controlled trial of a restrictive versus liberal red-cell transfusion strategy

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