# Integrating Health Care Data in an Informatics for Integrating Biology & the Bedside (i2b2) Model Persisted Through Elasticsearch: Design, Implementation, and Evaluation in a French University Hospital

## TL;DR

This paper describes how using Elasticsearch instead of a relational database improves the performance of the i2b2 model for health data analysis in a large hospital.

## Contribution

The paper introduces adaptations to the i2b2 model for Elasticsearch, enabling efficient query performance and reduced storage needs.

## Key findings

- Elasticsearch outperforms relational databases in query execution times, especially for free-text searches.
- Elasticsearch requires less disk space compared to indexed relational databases.
- The implementation is now in production at Bordeaux University Hospital.

## Abstract

The volume of digital data in health care is continually growing. In addition to its use in health care, the health data collected can also serve secondary purposes, such as research. In this context, clinical data warehouses (CDWs) provide the infrastructure and organization necessary to enhance the secondary use of health data. Various data models have been proposed for structuring data in a CDW, including the Informatics for Integrating Biology & the Bedside (i2b2) model, which relies on a relational database. However, this persistence approach can lead to performance issues when executing queries on massive data sets.

This study aims to describe the necessary transformations and their implementation to enable i2b2’s search engine to perform the phenotyping task using data persistence in a NoSQL Elasticsearch database.

This study compares data persistence in a standard relational database with a NoSQL Elasticsearch database in terms of query response and execution performance (focusing on counting queries based on structured data, numerical data, and free text, including temporal filtering) as well as material resource requirements. Additionally, the data loading and updating processes are described.

We propose adaptations to the i2b2 model to accommodate the specific features of Elasticsearch, particularly its inability to perform joins between different indexes. The implementation was tested and evaluated within the CDW of Bordeaux University Hospital, which contains data on 2.5 million patients and over 3 billion observations. Overall, Elasticsearch achieves shorter query execution times compared with a relational database, with particularly significant performance gains for free-text searches. Additionally, compared with an indexed relational database (including a full-text index), Elasticsearch requires less disk space for storage.

We demonstrate that implementing i2b2 with Elasticsearch is feasible and significantly improves query performance while reducing disk space usage. This implementation is currently in production at Bordeaux University Hospital.