The treatments for preventing and managing low cardiac output syndrome after congenital heart surgery with cardiopulmonary bypass include manipulations of vascular volume and infusions of phosphodiesterase inhibitors (milrinone) and catecholamines (epinephrine and norepinephrine) for inotropic and vasoactive effects, all of which have associated risks which can contribute to morbidity and mortality. Vasopressin, a vasoactive drug with efficacy in septic shock, has also been utilized to improve postoperative hemodynamics after cardiac surgery in children. It is a common institutional practice to use vasopressin in this patient population, but usually after escalation through two or three other vasoactive drugs. There have been several studies in pediatrics and adults which suggest that vasopressin is not inferior to other vasoconstrictor therapies, and advantageous when looking at specific end points. The investigators propose to randomize the use of vasopressin to use at an earlier point in our typical post-operative medication strategy. The proposed study is a double blinded, randomized, placebo control study of vasopressin infusion immediately after the completion Fontan operation. The goal is to identify a vasoactive treatment strategy that improves hemodynamics with lower catecholamine infusion burden, reduces volume of fluid resuscitation, and reduces in-hospital resource utilization.

Neonatal and pediatric interventions associated with congenital heart disease (CHD) continue to produce improved outcomes. There are no established guidelines for managing patients after congenital heart surgery due to lesion-specific unique challenges in the post-operative period. Volume resuscitation and catecholamine infusions are the traditional treatment methods to maintain adequate perfusion. However, these two treatment modalities are associated with increased risk of worsening lung function and prolonged ventilator support with aggressive fluid resuscitation, increased myocardial oxygen demand, and precipitation of arrhythmias. Given the multifactorial etiology of postoperative low cardiac output syndrome, it is often unclear which catecholamine infusion is optimal to improve circulatory function. Vasopressin, an alternative vasoactive therapy commonly utilized in shock, has been utilized to improve postoperative hemodynamics in neonatal and pediatric patient populations and has recently gained more attention.

The use of arginine vasopressin infusion in infants and children after cardiac surgery was first reported in 1999 in a case series of 11 patients with vasodilatory shock in the postoperative period. This case series reported initiation of vasopressin for hypotension refractory to traditional treatment methods and reported a significant rise in hemodynamics with improved blood pressure in all patients as well as weaning inotropic support in 10/11 patients. Since this study there have been conflicting reports regarding vasopressin levels and the use of vasopressin to improve hemodynamics. Results from a study published in 2008 evaluated vasopressin levels in 39 patients with CHD in the pre and post-operative periods and concluded that children do not have deficient levels of vasopressin following surgery with cardiopulmonary bypass (CPB). In addition, lower levels were not associated with hypotension. A larger study in 2010 of 121 patients who had congenital heart surgery with CPB described results suggestive of clinically important hypotension associated with low vasopressin levels. Several other publications have reported improved blood pressure and decreased catecholamine usage in patients with CHD. Two of these reports have focused on vasopressin use in infants with single ventricle physiology. In all of these reported case series the vasopressin infusion has been initiated in the post-operative period as a rescue therapy. None of the studies have advocated for initiation of vasopressin immediately post-operatively and prior to a time period of hemodynamic instability, except for one retrospective chart review by Alten et al. This study from 2012 initiated vasopressin in the operating room after CPB in 19 neonates undergoing either an arterial switch for d-transposition of the great arteries or the Norwood palliation procedure for hypoplastic left heart syndrome. In this study, all neonates in whom vasopressin was initiated in the operating room received significantly lower amounts of volume replacement and catecholamine support in the immediate post-operative period. They also described lower heart rate, lower incidence of arrhythmias, shorter duration of mechanical ventilation and shorter intensive care unit stay when compared to lesion-matched control group. More recently in 2016, a single center retrospectively reviewed their experience with vasopressin and patients undergoing Fontan operations over a 10 year period and it's effects on chest tube output. They determined that patients receiving vasopressin perioperatively had less chest tube output and shorter duration of chest tube drainage in addition to shorter hospital length of stay and improved fluid balance as compared to historical controls.

There is a gap in the literature describing improved outcomes with a specific targeted vasoactive and inotropic therapy regimen to use in the post-operative Fontan procedure patients. This proposed novel study will further provide evidence for outcome based post-operative medical interventions. The proposed study is a double blinded, randomized control study of vasopressin infusion versus placebo in the first 24-hours after Fontan completion. The aim of this study is to evaluate the impact of vasopressin on the early postoperative course in a relatively homogenous population, with specific attention to catecholamine use, hemodynamics, pleural drainage, extracardiac organ function (kidney and liver) and length of stay. Furthermore, the investigators plan to evaluate vasopressin levels between the two groups.