Intermediate Care Units Associated With Lower ICU Mortality and Better ICU Efficiency in Japan: Nationwide Cohort Analysis

Highlight

• In a nationwide Japanese database study of 2,278,521 adult ICU admissions (2016–2023), hospitals with an intermediate care unit (IMCU) had lower adjusted in-hospital and ICU mortality compared with hospitals without an IMCU.

• IMCU-equipped hospitals also showed fewer ICU readmissions, shorter ICU length of stay, higher ICU bed occupancy and life-sustaining therapy occupancy, and higher reimbursements and revenue per ICU bed, with only modest increases in hospitalization costs.

• Findings support integrating IMCUs into hospital critical care systems to improve patient outcomes and ICU efficiency, while highlighting remaining questions about variability, causality, and cost-effectiveness across settings.

Background

Demand for critical care services is rising globally. Intensive care units (ICUs) are resource-intensive, with constrained bed supply and high staffing costs, prompting interest in care models that optimize ICU utilization without compromising patient outcomes. Intermediate care units (IMCUs), also called high-dependency units or step-down/step-up units, provide an intermediate level of monitoring and therapy between general wards and ICUs. IMCUs can potentially (a) facilitate earlier ICU discharge for patients who remain at higher-than-ward risk, (b) provide monitored support for patients who do not require full ICU resources, and (c) serve as a buffer for ICU triage when demand fluctuates.

Despite theoretical benefits, evidence on IMCUs’ effect on patient-centered outcomes, ICU utilization, and hospital-level costs has been mixed, and many prior studies are single-center or limited by sample size. This nationwide retrospective cohort study from Japan evaluates patient-level outcomes and hospital-year-level utilization and cost metrics comparing hospitals with versus without an IMCU, using administrative inpatient data covering millions of admissions.

Study design

Design: Nationwide retrospective cohort analysis using Japan’s Diagnosis Procedure Combination Study Group database linked to Hospital Bed Function Reports from April 2016 to March 2023.

Population: 2,278,521 adult patients admitted to ICUs across 557 hospitals and 2,953 hospital-years.

Exposure: Hospital-level presence of an IMCU (hospitals with both an ICU and IMCU vs. hospitals with an ICU but no IMCU).

Outcomes: Patient-level— in-hospital mortality, ICU mortality, ICU readmission, and length of ICU stay. Hospital-year–level—ICU bed occupancy, occupancy for life-sustaining therapies, reimbursement rates, and annual revenue per ICU bed (in Japanese yen).

Analysis: The authors reported both participant-average treatment effects (patient-level adjusted analyses) and cluster-average treatment effects (hospital-year–level comparisons). Adjustment and modeling details were used to estimate adjusted odds ratios (aORs), adjusted rate ratios, mean differences, and 95% confidence intervals (CIs).

Key findings

Scope and transfers: Of the 2,278,521 ICU patients, 1,771,000 (77.7%) were cared for in hospitals that had both an ICU and IMCU. Across the cohort, 14.3% of patients experienced transfers between ICU and IMCU; transfer rates varied widely among hospitals.

Patient-level outcomes (participant-average treatment effect)

• In-hospital mortality: Patients in IMCU-equipped hospitals had modestly lower adjusted in-hospital mortality (aOR 0.94; 95% CI, 0.89–0.99). This corresponds to a relative reduction in odds of hospital death, after adjustment for available confounders.

• ICU mortality: ICU mortality was lower in IMCU-equipped hospitals (aOR 0.87; 95% CI, 0.83–0.92), indicating a larger relative association than for in-hospital mortality.

• ICU readmissions: ICU readmission rates were lower in IMCU hospitals (aOR 0.92; 95% CI, 0.85–1.00), a result that borders conventional statistical significance and suggests fewer premature ICU discharges or improved step-down monitoring.

• ICU length of stay: ICU stays were slightly shorter in IMCU-equipped hospitals (adjusted rate ratio 0.98; 95% CI, 0.98–0.99), representing a small but potentially systemically important reduction in resource days when aggregated across large populations.

Hospital-year–level outcomes (cluster-average treatment effect)

• ICU bed occupancy: Hospitals with an IMCU had higher mean ICU bed occupancy (mean difference: +5.5 percentage points; 95% CI, 3.3–7.7%).

• Occupancy for life-sustaining therapies: Occupancy for therapies such as mechanical ventilation, vasopressors, or renal replacement therapy was higher (mean difference: +8.6 percentage points; 95% CI, 7.7–9.5%), suggesting concentration of higher-acuity cases in IMCU-equipped centers.

• Reimbursement and revenue: IMCU hospitals had increased reimbursement rates (mean difference +5.4%; 95% CI, 4.0–6.8%) and higher annual revenue per ICU bed (mean difference ≈ 25 million JPY; 95% CI, 19–31 million JPY), indicating financial implications of IMCU integration—higher revenue and reimbursement with only modest increases in overall hospitalization costs reported by the authors.

Interpretation of magnitude

The observed effect sizes are modest at the patient level but potentially meaningful at population and system levels: small reductions in mortality and ICU length of stay multiplied by millions of ICU admissions and aggregated across hospital years could translate into substantial numbers of lives saved and ICU bed-days freed.

Expert commentary and critical appraisal

Strengths: This study benefits from an exceptionally large, nationwide dataset capturing millions of ICU admissions across multiple years, enabling high precision in estimates and assessment of hospital-level impacts. The authors analyzed both patient-average and cluster-average effects, providing complementary views of individual outcomes and system-level performance.

Biological and operational plausibility: IMCUs provide closer monitoring and earlier detection of deterioration than general wards, and more flexible allocation of staff and equipment than ICUs. These functions plausibly reduce ICU readmissions, expedite ICU discharge when appropriate, and concentrate very-high-acuity care in ICUs, consistent with the observed outcomes.

Limitations and alternative explanations:

• Observational design: Residual confounding and selection bias are possible. Hospitals that invest in IMCUs may differ in staffing, protocols, case-mix referral patterns, or unmeasured quality metrics that influence outcomes independently of IMCU presence.
• Heterogeneity of IMCUs: IMCUs vary in staffing ratios, physician coverage (intensivist vs ward physician), equipment, nurse skill mix, and admission/transfer criteria. The study treats IMCU presence as binary and cannot resolve which IMCU models confer most benefit.
• Data limitations: Administrative databases lack granular physiologic severity scores (e.g., APACHE/SAPS) that would help risk-adjust outcomes more precisely. Misclassification of transfers and variability in coding practices are possible.
• Generalisability: Results reflect the Japanese healthcare context (payment systems, ICU practice patterns, and hospital organization) and may not fully generalize to other countries with different critical care delivery models.

Implications for practice and policy

For hospital leaders and critical care policymakers, key takeaways are:

• Integrated IMCUs are associated with improved patient outcomes (lower ICU and in-hospital mortality, fewer readmissions) and more efficient ICU throughput (shorter ICU length of stay, higher occupancy), suggesting that IMCUs can play an important role in contemporary critical care systems.
• IMCUs may enable more concentrated provision of life-sustaining therapies within ICUs while permitting lower-intensity monitoring in a dedicated intermediate setting—supporting better resource allocation.
• Although IMCU integration correlated with higher reimbursements and revenue per ICU bed, overall increases in hospitalization costs were modest in the reported data. Hospitals considering IMCUs should therefore undertake local cost-effectiveness analyses that consider capital, staffing, and operational costs together with clinical benefits.

Research gaps and future directions

Recommended next steps include:

• Prospective comparative studies and pragmatic trials examining specific IMCU models (staffing ratios, physician coverage, nurse training, monitoring capability) to identify which configurations deliver the best outcomes and value.
• Analyses incorporating granular severity scores and patient-reported outcomes to further clarify patient-level benefit and equity implications.
• Cost-effectiveness studies that include longer-term outcomes (functional recovery, readmission beyond the index hospitalization) and societal costs.
• Implementation studies to define optimal triage criteria, handover protocols, and metrics for quality and safety across ICU–IMCU–ward transitions.

Conclusion

This large nationwide Japanese cohort study found that hospitals with IMCUs had modest but consistent associations with lower ICU and in-hospital mortality, fewer ICU readmissions, and shorter ICU length of stay, alongside higher ICU occupancy and revenue per bed. The results support the role of IMCUs as a component of efficient critical care systems, while recognizing the need for careful evaluation of IMCU models, local costs, and generalizability across healthcare systems.

Funding and clinicaltrials.gov

Funding: Not reported in the article abstract provided.

ClinicalTrials.gov: Not applicable (retrospective observational database study).

References

Ohbe H, Kudo D, Kimura Y, Matsui H, Fushimi K, Yasunaga H, Kushimoto S. Outcome, Process, Utilization, and Cost Measurements of Patients Admitted to the ICU in Hospitals With Vs. Without an Intermediate Care Unit: A Nationwide Inpatient Database Study. Crit Care Med. 2025 Nov 11. doi: 10.1097/CCM.0000000000006962 . Epub ahead of print. PMID: 41217377 .