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.