Purpose The Blalock-Taussig (BT) shunt is a surgical procedure that establishes a permanent source of pulmonary or systemic blood flow in children with severely obstructed or hypoplastic vessels. Post-operatively, one of the major challenges for the practitioner is to maintain a balanced pulmonary to systemic blood flow ratio. For those patients with persistently low oxygen saturations or concern for pulmonary hypertension, some practitioners empirically trial selective phosphodiesterase inhibitors in an attempt to increase pulmonary blood flow. The purpose of this retrospective study was to evaluate the patient characteristics, indication, side effects, and efficacy of the phosphodiesterase-5 inhibitor sildenafil in patients who are dependent on a BT shunt. Methods Infants who underwent surgical palliation with a BT shunt between January 2009 and May 2019 were identified through our surgical database. Of these patients, a retrospective chart review of all infants who were initiated on sildenafil during their first interstage period was performed. Interstage was defined as the time between placement of the BT shunt and the next surgical palliation or complete corrective surgery. Results Of the 308 patients who underwent BT shunt placement, 31 (10%) were started on sildenafil during the interstage period (Figure 1 and Table 1). The most common indications were concern for pulmonary hypertension (N=11), weaning nitric oxide (N=9), and persistent oxygen requirement/low oxygen saturation (N=9). Eighteen (58%) were on at least one inotropic agent at the time of initiation. The average starting dose was 1.19 mg/kg/day with an average of 7.1 days until mean maximum dose of 2.7mg/kg/day was achieved. Over half (54%) of patients were discharged on sildenafil. Five (16%) patients had an adverse event requiring dosing adjustment, holding of a dose, or discontinuation of the medication. The most common adverse events were hypotension (16%), worsening pulmonary edema (3%), and persistent oxygen saturation > 85%. Nine patients (29%) underwent a diagnostic cardiac catheterization after initiation and 7 (23%) patients had an intervention to increase pulmonary blood flow, including pulmonary artery angioplasty (N=3), repositioning of an ECMO canula (N=1), BT shunt angioplasty/stent (N=2), and ballooning of the innominate artery (N=1). Conclusions The vast majority of patients with shunted physiology who were initiated on sildenafil did not experience adverse effects. Patients who seem to be at most risk for adverse effects such as hypotension are those in the intensive care unit and on inotropic support. The indication, starting dose, and final dose of sildenafil vary widely. Additional analysis of this cohort and its subgroups may be helpful to determine the utility of its use in this physiologically fragile population.

Weeks, weight, and days are all listed as averages for the cohort. Abbreviations: kg – kilograms; mm – millimeters; ECMO – extracorporeal membranous oxygenation; S2P – stage 2 palliation