Relationship Between Discharge Practices and Intensive Care Unit In-Hospital Mortality Performance: Evidence of a Discharge Bias

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Context:Current intensive care unit performance measures include in-hospital mortality after intensive care unit admission. This measure does not account for deaths occurring after transfer to another hospital or soon after discharge and therefore, may be biased.Objective:Determine how transfer rates to other acute care hospitals and early post-discharge mortality rates impact hospital performance assessments using an in-hospital mortality model.Design, Setting, and Participants:Data were retrospectively collected on 10,502 eligible intensive care unit patients across 35 California hospitals between 2001 and 2004.Measures:We calculated the rates of acute care hospital transfers and early post-discharge mortality (30-day overall mortality—30-day in-hospital mortality) for each hospital. We assessed hospital performance with standardized mortality ratios (SMRs) using the Mortality Probability Model III. Using regression models, we explored the relationship between in-hospital SMRs and the rates of hospital transfers or early post-discharge mortality. We explored the same relationship using a 30-day SMR.Results:In multivariable models, for each 1% increase in patients transferred to another acute care hospital, there was an in-hospital SMR reduction of −0.021 (−0.040−0.001). Additionally, a 1% increase in early post-discharge mortality was associated with an in-hospital SMR reduction of −0.049 (−0.142–0.045). Assessing hospital performance based upon 30-day mortality end point resulted in SMRs closer to 1.0 for hospitals at high and low ends of in-hospital mortality performance.Conclusions:Variations in transfer rates and potentially discharge timing appear to bias in-hospital SMR calculations. A 30-day mortality model is a potential alternative that may limit this bias.

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