PROJECT SUMMARY/ABSTRACT Deimplementing overused health interventions is an essential step in maximizing quality and minimizing waste in the United States health care system. Acute bronchiolitis is a common lung disease of young children caused by respiratory viral infection. Continuous pulse oximetry monitoring in hospitalized infants with bronchiolitis who are not receiving supplemental oxygen is an overused intervention that has persisted despite evidence that it is ineffective in this population and may cause harm. Three national guidelines now discourage continuous pulse oximetry monitoring in hospitalized infants with bronchiolitis who are not receiving supplemental oxygen. In preliminary studies, the investigators showed that continuous pulse oximetry overuse occurs in nearly half of all hospitalized infants with bronchiolitis for whom there is no monitoring indication, and there is high between-hospital variability in overuse. The overarching goal of the applicants is to determine which strategies are most effective for deimplementing overused health interventions that have the potential to harm children. The overall objective of this application is to conduct the Eliminating Monitor Overuse (EMO) SpO2 trial, a hybrid type III effectiveness-deimplementation trial with a longitudinal cluster-randomized design in 32 Pediatric Research in Inpatient Settings Network hospitals. The trial will test an unlearning deimplementation strategy (educational outreach with audit & feedback) vs. a combined unlearning + substitution deimplementation strategy (adding an electronic health record-integrated clinical pathway) on sustainability of continuous pulse oximetry monitoring deimplementation in children with bronchiolitis who are not receiving supplemental oxygen. This proposal includes three Specific Aims: (1) Compare the effects of the unlearning only strategy versus the unlearning + substitution strategy on deimplementation outcomes, (2) Identify deimplementation strategy mechanisms linked to penetration and sustainability using mixed methods, and (3) Examine the effects of deimplementation on clinical outcomes and unintended consequences. This approach is innovative because it focuses on the under-researched area of pediatric deimplementation, the experimental design reflects state-of-the-art theoretical framing of deimplementation interventions, and the primary outcome focuses on long-term sustainability of deimplementation, which is highly relevant to the public. The proposed research is significant because it will advance the science of health care delivery for a high incidence pediatric lung disease that hospitalizes 100,000 children annually, acute viral bronchiolitis. The trial will also provide new insights into the processes, mechanisms, costs, and outcomes of large, rigorously- designed deimplementation efforts.