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Comparing observed and predicted mortality among ICUs using different prognostic systems: why do performance

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  • 11Cerner Corporation, Vienna, VA. 2Department of Biostatistics, Kansas University Medical Center, Kansas City, MO. 3Critical Care Division, Department of Medicine, Baystate Medical Center, Springfield, MA. 4Tufts University School of Medicine, Boston, MA. 5Department of Anesthesiology and Critical Care Medicine, George Washington University, Washington, DC.

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Summary
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Standardized mortality ratios (SMRs) for intensive care units (ICUs) differ significantly between the Acute Physiology and Chronic Health Evaluation IVa (APACHE IVa) and National Quality Forum (NQF) models. These discrepancies arise from variations in case-mix adjustment, impacting ICU performance assessments.

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Area of Science:

  • Critical Care Medicine
  • Health Services Research
  • Biostatistics

Background:

  • Standardized mortality ratios (SMRs) are crucial for assessing intensive care unit (ICU) performance.
  • Existing models, such as Acute Physiology and Chronic Health Evaluation IVa (APACHE IVa) and National Quality Forum (NQF) methodologies, are used for SMR generation.
  • Differences in these models can lead to varied interpretations of ICU quality.

Purpose of the Study:

  • To compare ICU performance using SMRs generated by APACHE IVa and an NQF-endorsed methodology.
  • To investigate the reasons behind discrepancies in model-based SMRs.
  • To evaluate the impact of case-mix adjustment on ICU performance metrics.

Main Methods:

  • Retrospective analysis of day 1 hospital mortality predictions at the ICU level.
  • Utilized data from 47 ICUs across 36 U.S. hospitals (January 2008 - May 2013).
  • Included 89,353 consecutive ICU admissions, comparing APACHE IVa and NQF models on the same patient cohort.

Main Results:

  • Overall SMRs were 0.89 for APACHE IVa and 1.07 for NQF, with NQF showing wider SMR distribution.
  • Model exclusion criteria affected 10.6% of patients for APACHE IVa and 27.9% for NQF.
  • Agreement between models on SMR significance and direction was only 45%; discordant SMRs were linked to sicker patients and higher mechanical ventilation rates.

Conclusions:

  • APACHE IVa and NQF models provide different ICU performance assessments due to distinct case-mix adjustments.
  • The study highlights the need for models with fewer exclusions and superior accuracy for reliable performance evaluation.
  • Given the influence of outcomes on healthcare policy, robust case-mix adjustment is essential for fair ICU performance assessment.