Propranolol Treatment for Postoperative Chylothorax

This clinical trial will prospectively enroll eligible patients and randomize them to placebo or propranolol (1:1). This study will aim to enroll 50 patients, randomized to 25 placebo and 25 propranolol treatment. After patients have been consented, registered, and screened, they will be entered into the study. Participants will be randomized to placebo or propranolol in a 1:1 ratio. Randomization will be double-blinded, and each enrolled participant will be given a number and receive coded medication from the research pharmacy. Patients may undergo a screening MR lymphangiogram (MRL) prior to starting treatment. The criteria for an MRL will require that no additional sedation be given, and patient or parent/legal guardian consents to an MRL. Thus, only patients who are already sedated, or who will be able to undergo the MRL without sedation, and who opts in to the MRL will be eligible. Propranolol or placebo will be administered for 9 days after reaching the lowest effective goal dose not to exceed 2mg/kg/day, or maximum tolerated dose, after which the study groups will be unmasked. Participants who have ≥80% reduction in volume of chylothorax drainage after 9 days of treatment and who received propranolol are identified as "responders". They will be taken off the study officially at this point as no more study interventions will be given. They will be tapered off of propranolol gradually as clinically indicated. Participants who have ≥80% reduction in volume of chylothorax drainage but who received placebo will be the "natural history cohort". This will serve to demonstrate, as baseline, the percentage of participants who naturally resolve their chylothorax without intervention. Patients who have \<80% reduction in chylothorax drainage and who received propranolol, will be categorized as initial "non-responders". They will be officially taken off the study. Participants who have \<80% reduction in chylothorax drainage and who received placebo are considered a control group. They will be given propranolol for 9 days as a single-arm, open study and re-evaluated after a 9-day treatment. After 9 days at goal dosing, they will receive the same treatment as the responders and non-responders in the propranolol-treated group.