This retrospective observational study used data from the Japan Trauma Data Bank. The study was conducted from January 2004 to December 2021. The JTDB is required to register all severe trauma cases with AIS 3 or higher injuries and was established by the Japanese Association for Acute Medicine and Japanese Association for The Surgery of Trauma to understand the current status and improve the quality of trauma care, akin to the Trauma Quality Improvement Program in the United States. By the end of December 2021, the JTDB included 303 facilities providing trauma care in Japan, of which 95% were government-certified tertiary care centers.

In Japan, trauma patients are usually transported by ambulance staffed with paramedics, although physician-staffed ground or air ambulance is dispatched to the field in some cases. However, REBOA is rarely performed in pre-hospital settings and is often performed after arrival at the emergency department. Moreover, blood transfusion is rarely performed in pre-hospital settings.

This study complied with the principles of the 1964 Declaration of Helsinki and its amendments and was approved by the Ethics Committee of Tsuchiura Kyodo General Hospital (approval number: 2022FY10). The requirement for informed consent from each patient was waived because of the study’s retrospective nature. We used the opt-out method, which provides opportunities to refuse to participate in the study through online information disclosure in our hospital. The study was conducted in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting statement.

The study included all cases for which REBOA was used between 2004 and 2021.

We collected the following patient information from the JTDB: age; sex; year of injury; trauma classification (blunt or penetrating); pre-hospital vital signs [systolic blood pressure (SBP), heart rate (HR), respiratory rate (RR), and percutaneous oxygen saturation (SpO2)]; Glasgow coma scale (GCS) score; time from emergency medical service dispatch to emergency department (ED) arrival; vital signs at ED arrival [SBP, HR, RR, and SpO2, body temperature, and GCS, abbreviated injury scale (AIS) score for each region, injury severity score (ISS), revised trauma score (RTS), status at hospital discharge (survival or death)]; lactic acid level; focused assessment with sonography in trauma (FAST) results; number of REBOA cases, cases of cardiac arrest on arrival, and ACC cases; and probability of survival based on the trauma and injury severity score (TRISS-Ps).

The AIS was calculated based on AIS 98 until 2018 and AIS 2008 after 2019 in accordance with the change in JTDB registration rule. Data for pre-hospital GCS score, SpO2, and lactic acid levels on ED arrival were only available after 2019 in the JTDB. Cardiac arrest was characterized by a recorded SBP of 0 mmHg based on the registration instructions of the JTDB. The primary outcome was survival at hospital discharge.

The trend of the number, characteristics, and outcomes of patients treated with REBOA and the number of facilities where REBOA was used, according to admission year, was described. Trends in hospital mortality were also compared among specific subgroups, including all patients with trauma, patients treated with REBOA, patients treated with REBOA without severe head or spine injuries defined by AIS ≥ 3, patients treated with REBOA with shock upon hospital arrival (SBP < 80 mmHg), and patients treated with REBOA without shock upon hospital arrival.

Patient characteristics were described using median and interquartile range (IQR) for continuous variables and number and percentage (%) for categorical variables. The chi-square test was used with a significance level of 0.05 to test the association of variables. We conducted a single regression analysis to show the changes in annual mortality rates across some subgroups: all patients with trauma in the database, all cases in which REBOA was used, the REBOA group without severe head or spine injury of AIS ≥ 3, cases with SBP < 80 mmHg among patients for whom REBOA was used, and patients with SBP ≥ 80 mmHg among patients for whom REBOA was used. We conducted a logistic regression analysis for the annual mortality rate adjusted by TRISS-Ps. All statistical analyses were performed using R software version 4.3.1 (R Foundation for Statistical Computing, Vienna, Austria).