RESULTS: In LCN2 -/- SBR mice, IL-22 gene expression in the small intestine significantly increased, and IL-22 serum levels were maintained; and in WT SBR mice, both decreased. CD4 + IL-22 + laminal propria lymphocytes significantly increased in LCN2 -/- SBR mice but decreased in WT SBR mice. In vitro, naı ¨ve CD4 + T cells that differentiated to Th22 cells secreted IL- 22 in the supernatant. Importantly, IL-22 levels significantly decreased in the presence of LCN2 (Figure). CONCLUSIONS: Lipocalin 2 inhibits IL-22 expression in SBS. Neutralizing LCN2 can be a novel therapeutic target to improve intestinal adaptation. Market Evaluation of the Pediatric Surgical Workforce in US Children’s Hospitals Liese CC Pruitt, MD, Zachary J Kastenberg, MD, David E Skarda, MD, FACS, Brian T Bucher, MD, FACS University of Utah, Salt Lake City, UT INTRODUCTION: With the number of pediatric surgeons increasing nationally, there has been concern about the operative volume of practicing pediatric surgeons. We elected to model the distribution of complex neonatal procedures at US children’s hos- pitals using an economic measure of market concentration, the Herfindahl-Hirschmann Index. METHODS: We used data from 49 US children’s hospitals be- tween 2007 and 2017 for the following neonatal procedures: congenital diaphragmatic hernia repair, esophageal and tracheoeso- phageal fistula repair, gastroschisis and omphalocele closures, neonatal bowel resections, and pull-throughs for Hirschsprung dis- ease. Surgeon volume was calculated using unique surgeon identi- fiers at each hospital. Surgeon specialization within each hospital was measured per hospital per year using the Herfindahl-Hirsch- mann Index: the sum of the squared proportion of cases performed by the surgeons at each hospital. RESULTS: The number of surgeon identifiers per year ranged from 437 to 733, as the number of hospitals increased from 41 to 49. Surgical workforce (mean surgeons per hospital) ranged from 11 to 15 and the mean neonatal cases per hospital ranged from 8 to 15. Median Herfindahl-Hirschmann Index was 0.18 in 2007 and 0.13 in 2017, which was a significant decrease (p ¼ 0.02). In 2007, 64% of hospitals fell in the moderately to highly concentrated range, which decreased to 40% in 2017, approaching statistical significance (p ¼ 0.08). There was significant negative correlation between the size of the surgical workforce and HHI (r ¼ -0.21; p < 0.001), (Figure). CONCLUSIONS: Increasing pediatric surgical workforce has led to decreased specialization by hospital. This implies that as the num- ber of pediatric surgeons grows, the index neonatal cases are being distributed between more surgeons. Morbidity of Conversion from Veno-Venous to Veno-Arterial Extracorporeal Membrane Oxygenation in Neonates with Meconium Aspiration or Persistent Pulmonary Hypertension Beatrix H Choi, Bridget Toy, RN, Heda Dapul, MD, Sourabh Verma, MD, Erin Cicalese, MD, Arun Chopra, MD, Jason C Fisher, MD, FACS, FAAP NYU Langone Health, New York, NY; NYU School of Medicine, New York, NY INTRODUCTION: Outcomes in neonates requiring extracorporeal membrane oxygenation (ECMO) for meconium aspiration syn- drome (MAS) and/or persistent pulmonary hypertension (PPHN) are favorable. Infants with preserved systemic perfusion can undergo veno-venous (VV) support to spare morbidities of veno-arterial (VA) ECMO. Worsening perfusion or circuit complications can prompt conversion from VV to VA support. We examined outcomes in MAS/PPHN infants requiring VA ECMO based on whether they underwent VA support initially or were converted to VA after a VV trial, and analyzed factors pre- dicting conversion. METHODS: We reviewed the Extracorporeal Life Support Organization registry from 2007 to 2017 for neonates with MAS/PPHN. Propensity score analysis matched VA single-runs (controls) 4:1 against VV to VA conversions based on age, pre-ECMO pH, and precannulation arrests. Primary outcomes were complications and survival. Data were assessed using Mann-Whitney U test, Fisher’s exact test, and multivariate regression analyses. RESULTS: A total of 3,831 neonates underwent ECMO for MAS/PPHN, including 2,129 (55%) initially requiring VA sup- port. Of 1,702 patients initially placed on VV ECMO, 98 (5.8%) required VV to VA conversion. Compared with 364 pro- pensity-matched single-run VA controls, conversion runs were longer and associated with more complications and decreased sur- vival (Table). On multivariate regression, conversion was more likely if neonates on VV ECMO did not receive surfactant (odds ratio 1.9; 95% CI 1.1 to 2.7; p ¼ 0.01) or required high-frequency ventilation (odds ratio 1.7; 95% CI 1.2 to 3.3; p ¼ 0.03) before ECMO. CONCLUSIONS: Conversion from VV to VA ECMO in MAS/ PPHN conveys increased morbidity and mortality compared Figure. S208 Scientific Forum Abstracts J Am Coll Surg