Patients with Fontan circulation represent a unique and physiologically vulnerable population in the CICU.¹ The Fontan procedure, originally developed for tricuspid atresia, is now used to manage several congenital heart defects characterized by single-ventricle physiology.² In this circulation, the superior and inferior venae cavae are surgically connected to the pulmonary arteries, eliminating the need for a subpulmonary ventricle. Thus, pulmonary blood flow occurs passively and is driven by the pressure gradient between the systemic venous circulation and the pulmonary vasculature.^2,3

In the absence of a subpulmonary ventricle, cardiac output in Fontan physiology is critically dependent on maintaining low PVR.⁴ Any factor that increases PVR, including hypoxemia, acidosis, inflammation, or elevated intrathoracic pressure, can significantly impair pulmonary blood flow and reduce ventricular preload. Unlike biventricular circulation, in which ventricular contractility frequently contributes to low cardiac output in shock, Fontan circulation is typically limited by impaired preload rather than intrinsic systolic dysfunction.^3,5

This patient developed septic shock in the setting of pneumonia and hypoxemic respiratory failure. Infection-related inflammation, hypoxemia, and tachypnea all contribute to elevations in PVR and lead to reductions in cardiac output with consequent hypotension, even in the absence of primary ventricular dysfunction.¹

Escalation of norepinephrine to support systemic perfusion would be the most appropriate management strategy because, in patients with Fontan physiology, pulmonary blood flow occurs passively from the systemic venous circulation into the pulmonary arteries and is highly dependent on maintaining low PVR. In this setting, cardiac output is primarily limited by impaired ventricular preload rather than intrinsic ventricular contractile dysfunction.^2-4 Norepinephrine is preferred in this scenario because it increases systemic vascular resistance (SVR) to a greater extent than PVR, thereby improving systemic arterial pressure and coronary perfusion pressure without significantly impairing pulmonary blood flow. In Fontan patients, maintaining adequate systemic perfusion pressure is particularly important because cardiac output reserve is limited and coronary perfusion may already be compromised by chronically elevated central venous pressures.¹ By supporting systemic perfusion while minimizing adverse effects on the pulmonary circulation, norepinephrine represents the most appropriate first-line vasoactive agent in this patient's current condition.

Although dobutamine may reduce PVR through beta-2–mediated vasodilation, it does not address the primary limitation leading to reduced cardiac output in Fontan physiology, namely impaired ventricular preload. In addition, dobutamine lowers SVR and may worsen hypotension in the setting of sepsis, often necessitating escalation of vasopressor support. In the acutely ill patient with Fontan physiology, inotropic therapy may therefore increase myocardial O₂ demand and HR without reliably improving cardiac output. Consequently, inotropes are generally reserved for select cases in which ventricular systolic dysfunction is clearly contributing to hemodynamic instability after preload and systemic perfusion have been optimized.⁵

Use of high PEEP ventilation during mechanical ventilation to improve oxygenation is an incorrect choice because high levels of PEEP increase intrathoracic pressure, consequently increasing PVR. In Fontan physiology, increased airway pressures are transmitted to the pulmonary vasculature and systemic venous circulation, impeding passive pulmonary blood flow and further limiting ventricular preload.³ Although mechanical ventilation may be required in cases of severe hypoxemic respiratory failure, ventilatory strategies in Fontan patients should be carefully selected to minimize mean airway pressures and peak end-expiratory pressures to avoid exacerbating hemodynamic compromise.

Hypoxemia induces hypoxic pulmonary vasoconstriction, which increases PVR and worsens ventricular preload limitation in Fontan circulation.⁴ Accepting lower O₂ saturations in this patient population may be counterproductive because worsening hypoxemia can further impair pulmonary blood flow and reduce cardiac output. In contrast to some cyanotic congenital heart diseases, adequate oxygenation in Fontan patients is critical to maintaining low PVR and preserving effective cardiac output.

References

1. Valle CW, Garfinkel AC, Buber J, et al. Critical care of the adult with congenital heart disease. JACC Adv. 2025;4(10 Pt 1):102081. doi:10.1016/j.jacadv.2025.102081
2. Rychik J, Atz AM, Celermajer DS, et al. Evaluation and management of the child and adult with fontan circulation: a scientific statement from the American Heart Association. Circulation. 2019;140(6):e234-e284. doi:10.1161/CIR.0000000000000696
3. Gewillig M, Brown SC. The Fontan circulation after 45 years: update in physiology. Heart. 2016;102(14):1081-1086. doi:10.1136/heartjnl-2015-307467
4. Liang F, Senzaki H, Kurishima C, Sughimoto K, Inuzuka R, Liu H. Hemodynamic performance of the Fontan circulation compared with a normal biventricular circulation: a computational model study. Am J Physiol Heart Circ Physiol. 2014;307(7):H1056-H1072. doi:10.1152/ajpheart.00245.2014
5. Senzaki H, Masutani S, Ishido H, et al. Cardiac rest and reserve function in patients with Fontan circulation. J Am Coll Cardiol. 2006;47(12):2528-2535. doi:10.1016/j.jacc.2006.03.022