Study design and setting
We performed a retrospective analysis of the Japan Trauma Data Bank (JTDB). The institutional ethics committee of Osaka University Graduate School of Medicine approved this study and waived the requirement for informed consent because all of the analyses used anonymous data (approval no. 16260).
Japan Trauma Data Bank
The JTDB is a nationwide voluntary hospital-based trauma registry that was established in 2003 by the Japanese Association for the Surgery and Trauma (Trauma Surgery Committee) and the Japanese Association for Acute Medicine (Committee for Clinical Care Evaluation).13 In 2018, 280 major emergency medical institutions across Japan participated in the JTDB registry.14 The ability of these hospitals is equivalent to that of level I trauma centers in the United States. Data were collected from participating institutions via the internet. In most cases, physicians and medical assistants who completed the Abbreviated Injury Scale (AIS) coding course registered the patients’ data.
The JTDB captures the following data in trauma cases: age, sex, mechanism of injury, AIS code (version 1998), Injury Severity Score (ISS), vital signs on hospital arrival, date and time series from hospital arrival to discharge, medical managements (e.g., interventional radiology), surgical operations and computed tomography scanning, complications, and mortality at discharge. The ISS was calculated from the top three scores of the AIS in the nine anatomical regions classified by the AIS code.
Participants
The cases of patients who were admitted in the years 2004 to 2018 and whose information was registered in the JTDB were analyzed. We included blunt trauma patients with traumatic renal injuries, which were identified by AIS codes using the method described by Kuan et al.12 AIS codes were converted to AAST renal injury grades, excluding codes that did not match.15,16,17 We excluded patients who were in cardiac arrest on hospital arrival, and those whose records were missing information on age, sex, vital signs on arrival, ISS, or mortality. We defined cardiac arrest on hospital arrival as a systolic blood pressure of 0 mmHg or a heart rate of 0 bpm on hospital arrival.
Variables
We extracted the following patient data from the JTDB database: age, sex, mechanism of injury, AIS code, ISS, vital signs on hospital arrival, interventions (e.g., emergency abdominal angiography or nephrectomy), and mortality at discharge. To evaluate temporal trends, we divided the 15-year study period into five periods: 2004-2006, 2007-2009, 2010-2012, 2013-2015, and 2016-2018. We categorized age into three groups: <20 years, 20–64 years, and ≥65 years. We defined shock as a systolic blood pressure of <80 mmHg on hospital arrival.18 To assess concomitant injuries, we mapped AIS-coded injuries to the following categories: head/neck, thorax, pelvis/extremities, and intra-abdominal organs (including the liver, spleen, pancreas, and gastrointestinal tract).
Statistical analyses
Continuous variables are presented as the median and interquartile range (IQR) and categorical variables are presented as the number and percentage. The Jonckheere-Terpstra test was used to analyze trends in continuous variables and the Cochrane-Armitage test was used to analyze trends in categorical variables.
Factors associated with mortality were assessed by a multivariable logistic regression analysis and adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. A multivariable logistic regression analysis was performed with a forced entry procedure. The independent parameters included age group (<20 years, 20-64 years, ≥65 years), sex, mechanism of injury, shock on arrival, each concomitant injury, AAST renal injury grade, and interventions (e.g., emergency abdominal angiography or nephrectomy), and the 3-year time period. We also assessed factors associated with nephrectomy using a multivariable logistic regression analysis. The fit of the models was evaluated with the Hosmer-Lemeshow goodness-of-fit test.
As a further analysis, we divided patients into those with isolated renal trauma and those with multiple trauma to evaluate the difference in patient demographics. The patient characteristics were compared between the groups using the Mann-Whitney U test for continuous variables and the chi-squared test for categorical variables.
All tests were two-tailed, and P values of <0.05 were considered to indicate statistical significance. All statistical analyses were performed using R Statistical Software (version 3.6.2; R Foundation for Statistical Computing, Vienna, Austria).