Data source
In this nationwide retrospective cohort study, we used data from the Japanese Diagnosis Procedure Combination database, the details of which have been described elsewhere.9 Briefly, this database includes data of approximately 7 million inpatients per year, which represent more than half of all inpatient admissions to acute care hospitals in Japan. The database includes the following characteristics for each patient: age, sex, body height, weight, Japan Coma Scale score, smoking status, diagnoses, pre-admission comorbidities, post-admission complications, medications, and discharge status. Diagnoses are recorded using the International Classification of Disease 10th revision (ICD-10) codes. The Institutional Review Board of The University of Tokyo approved this study (Approval Number, 3501-3; 25 December 2017). Because the data were anonymized, the requirement for informed consent was waived.