Standardizing ICU Data Across Europe: Development of the INDICATE Minimal Data Dictionary

Building federated infrastructure for European ICU data requires establishing standards for semantic interoperability across heterogeneous clinical settings. Even with standardized terminologies like LOINC and SNOMED CT, a single clinical concept may correspond to hundreds of alternative codes, precluding interoperability without explicit harmonization guidance. We developed the INDICATE Minimal Data Dictionary through an iterative, consensus-based process involving clinical experts and data scientists. The dictionary defines standardized OHDSI concept sets across nine clinical domains and supports six concrete use cases. Implementation is supported by a web-based application that provides expert-curated guidance for terminology selection and mapping. This approach reduces terminology ambiguity while remaining adaptable to local ICU practices, enabling scalable data harmonization across 15 European data providers from 12 countries.