Intensive care unit (ICU)-acquired bacteraemia and ICU mortality and discharge: addressing time-varying confounding using appropriate methodology

K. B. Pouwels*, S. Vansteelandt, R. Batra, J. D. Edgeworth, Timo Smieszek, Julie Robotham

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    21 Citations (Scopus)

    Abstract

    Background: Studies often ignore time-varying confounding or may use inappropriate methodology to adjust for time-varying confounding. Aim: To estimate the effect of intensive care unit (ICU)-acquired bacteraemia on ICU mortality and discharge using appropriate methodology. Methods: Marginal structural models with inverse probability weighting were used to estimate the ICU mortality and discharge associated with ICU-acquired bacteraemia among patients who stayed more than two days at the general ICU of a London teaching hospital and remained bacteraemia-free during those first two days. For comparison, the same associations were evaluated with (i) a conventional Cox model, adjusting only for baseline confounders and (ii) a Cox model adjusting for baseline and time-varying confounders. Findings: Using the marginal structural model with inverse probability weighting, bacteraemia was associated with an increase in ICU mortality (cause-specific hazard ratio (CSHR): 1.29; 95% confidence interval (CI): 1.02–1.63) and a decrease in discharge (CSHR: 0.52; 95% CI: 0.45–0.60). By 60 days, among patients still in the ICU after two days and without prior bacteraemia, 8.0% of ICU deaths could be prevented by preventing all ICU-acquired bacteraemia cases. The conventional Cox model adjusting for time-varying confounders gave substantially different results [for ICU mortality, CSHR: 1.08 (95% CI: 0.88–1.32); for discharge, CSHR: 0.68 (95% CI: 0.60–0.77)]. Conclusion: In this study, even after adjusting for the timing of acquiring bacteraemia and time-varying confounding using inverse probability weighting for marginal structural models, ICU-acquired bacteraemia was associated with a decreased daily ICU discharge risk and an increased risk of ICU mortality.

    Original languageEnglish
    Pages (from-to)42-47
    Number of pages6
    JournalJournal of Hospital Infection
    Volume99
    Issue number1
    DOIs
    Publication statusPublished - May 2018

    Bibliographical note

    Funding Information:
    This research was supported by the National Institute for Health Research (NIHR) Biomedical Research Centre based at Guy's and St Thomas' NHS Foundation Trust and King's College London, programme of Infection and Immunity (RJ112/N027) awarded to J.E., and the NIHR Collaboration for Leadership in Applied Health Research and Care (CLAHRC) South London at King's College Hospital NHS Foundation Trust, awarded to J.E. and R.B.

    Funding Information:
    This research was supported by the National Institute for Health Research (NIHR) Biomedical Research Centre based at Guy's and St Thomas' NHS Foundation Trust and King's College London , programme of Infection and Immunity ( RJ112/N027 ) awarded to J.E., and the NIHR Collaboration for Leadership in Applied Health Research and Care (CLAHRC) South London at King's College Hospital NHS Foundation Trust, awarded to J.E. and R.B.

    Publisher Copyright:
    © 2017

    Keywords

    • Bacteraemia
    • Bias
    • Burden
    • Intensive care units
    • Inverse probability weighting

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