The influence of volume and intensive care unit organization on hospital mortality in patients admitted with severe sepsis: a retrospective multicentre cohort study

Abstract

Introduction: The aim of the study was to assess the influence of annual volume and factors related to intensive care unit (ICU) organization on in-hospital mortality among patients admitted to the ICU with severe sepsis.

Methods: A retrospective cohort study was conducted using the database of the Dutch National Intensive Care Evaluation (NICE) registry. Analyses were based on consecutive patients admitted between 1 January 2003 and 30 June 2005 who fulfilled criteria for severe sepsis within the first 24 hours of admission. A 13-item questionnaire was sent to all 32 ICUs across The Netherlands that participated in the NICE registry within this period in order to obtain information on ICU organization and staffing. The association between in-hospital mortality and factors related to ICU organization was investigated using logistic regression analysis, combined with generalized estimation equations to account for potential correlations of outcomes within ICUs. Correction for patient-related factors took place by including Simplified Acute Physiology Score II, age, sex and number of dysfunctioning organ systems in the analyses.

Results: Analyses based on 4,605 patients from 28 ICUs (questionnaire response rate 90.6%) revealed that a higher annual volume of severe sepsis patients is associated with a lower in-hospital mortality (P = 0.029). The presence of a medium care unit (MCU) as a step-down facility with intermediate care is associated with a higher in-hospital mortality (P = 0.013). For other items regarding ICU organization, no independent significant relationships with in-hospital mortality were found.

Conclusion: A larger annual volume of patients with severe sepsis admitted to Dutch ICUs is associated with lower in-hospital mortality in this patient group. The presence of a MCU as a step-down facility is associated with greater in-hospital mortality. No other significant associations between in-hospital mortality and factors related to ICU organization were found.

Figure 1

ICU-specific RAMRs for patients admitted with severe sepsis. Values denote the risk-adjusted mortality rate (RAMR) with 95% confidence interval for each of the 28 Dutch intensive care units (ICUs) participating in the study. The RAMR was calculated as follows: based on the case-mix correction model (which included the variables age, sex, SAPS II score, and number of dysfunctioning organ systems), the standardized mortality ratio (SMR) was calculated for each ICU by dividing the observed number of deaths by the number of deaths as expected by the model. The RAMR was subsequently calculated by multiplying the SMR with the overall mean mortality rate in the population of patients admitted with severe sepsis. Values are based on all patients admitted with severe sepsis between 1 January 2003 and 30 June 2005.