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The Volume-Outcome Relationship in Critically Ill Patients in Relation to the ICU-to-Hospital Bed Ratio*

Sasabuchi, Yusuke MD1,2; Yasunaga, Hideo MD, PhD1; Matsui, Hiroki MPH1; Lefor, Alan K. MD, MPH, PhD3; Horiguchi, Hiromasa PhD4; Fushimi, Kiyohide MD, PhD5; Sanui, Masamitsu MD, PhD2

doi: 10.1097/CCM.0000000000000943
Clinical Investigations

Objectives: A volume-outcome relationship in ICU patients has been suggested in recent studies. However, it is unclear whether the ICU-to-hospital bed ratio affects the volume-outcome relationship. The aim of this study is to investigate the relationship between hospital volume and in-hospital mortality of adult ICU patients in relation to the ratio of ICU beds to regular hospital beds.

Design: Retrospective cohort study.

Setting: Four hundred seventy-seven Japanese hospitals from 2007 to 2012 in the Japanese Diagnosis Procedure Combination database.

Patients: A total of 596,143 patients discharged from acute care hospitals.

Interventions: None.

Measurements and Main Results: We analyzed data from 596,143 ICU patients from 2007 through 2012 using a nationwide administrative database. Patients were categorized into nine subgroups (the tertiles of hospital volume of ICU patients combined with the tertiles of ICU-to-hospital bed ratio). Multivariable logistic regression analyses were performed to examine the concurrent effects of hospital volume of ICU patients and ICU-to-hospital bed ratio on in-hospital mortality, with adjustment for patient and hospital characteristics. Higher hospital volume of ICU patients and a higher ICU-to-hospital bed ratio were independently associated with lower mortality. When patients were stratified by ICU-to-hospital bed ratio categories, in-hospital mortality was significantly lower in the high-volume subgroup (odds ratio, 0.74; 95% CI, 0.58–0.93) compared with the low-volume subgroup in hospitals with a high ICU-to-hospital bed ratio. However, these relationships were not significant in hospitals with low ICU-to-hospital bed ratios (odds ratio, 0.94; 95% CI, 0.59–1.50) or in hospitals with intermediate ICU-to-hospital bed ratios (odds ratio, 0.80; 95% CI, 0.71–1.08).

Conclusions: An inverse relationship between hospital volume of ICU patients and mortality was seen only when the ICU-to-hospital bed ratio was sufficiently high. Regionalization and increasing the number of ICU beds in referral centers may improve patient outcomes.

1Department of Clinical Epidemiology and Health Economics, School of Public Health, The University of Tokyo, Tokyo, Japan.

2Department of Anesthesiology and Critical Care Medicine, Jichi Medical University Saitama Medical Center, Saitama, Japan.

3Department of Surgery, Jichi Medical University, Tochigi, Japan.

4Department of Clinical Data Management and Research, Clinical Research Center, National Hospital Organization Headquarters, Tokyo, Japan.

5Department of Health Policy and Informatics, Tokyo Medical and Dental University Graduate School of Medicine, Tokyo, Japan.

* See also p. 1338.

This study was performed at School of Public Health, The University of Tokyo, Tokyo, Japan.

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Supported, in part, by a grant from the Ministry of Health, Labour and Welfare, Japan (Research on Policy Planning and Evaluation grant number: H26-Policy-011).

Drs. Sasabuchi, Yasunaga, Matsui, Lefor, Horiguchi, and Fushimi’s institutions received grant support from the Japanese Government. Dr. Sanui has disclosed that he does not have any potential conflicts of interest.

Address requests for reprints to: Yusuke Sasabuchi, MD, Department of Clinical Epidemiology and Health Economics, School of Public Health, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 1130033, Japan. E-mail:

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