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Heterogeneity of treatment effect by baseline risk of mortality in critically ill patients: re-analysis of three recent sepsis and ARDS randomised controlled trials

  • Santhakumaran, Shalini1
  • Gordon, Anthony2
  • Prevost, A. Toby1
  • O’Kane, Cecilia3
  • McAuley, Daniel F.3, 4
  • Shankar-Hari, Manu5, 6
  • 1 School of Public Health, Imperial College London, Imperial Clinical Trials Unit, London, W12 7RH, UK , London (United Kingdom)
  • 2 Imperial College London, Section of Anaesthetics, Pain Medicine and Intensive Care, London, W2 1NY, UK , London (United Kingdom)
  • 3 Wellcome-Wolfson Institute for Experimental Medicine, Centre for Experimental Medicine, Belfast, BT9 7AE, UK , Belfast (United Kingdom)
  • 4 Royal Victoria Hospital, Regional Intensive Care Unit, Belfast, BT12 6BA, UK , Belfast (United Kingdom)
  • 5 St Thomas’ Hospital, Guy’s and St Thomas’ NHS Foundation Trust, Department of Intensive Care Medicine, Westminster Bridge Road, London, SE1 7EH, UK , London (United Kingdom)
  • 6 School of Immunology & Microbial Sciences, King’s College London, Peter Gorer Department of Immunobiology, London, SE1 9RT, UK , London (United Kingdom)
Published Article
Critical Care
BioMed Central
Publication Date
May 03, 2019
DOI: 10.1186/s13054-019-2446-1
Springer Nature


BackgroundRandomised controlled trials (RCTs) enrolling patients with sepsis or acute respiratory distress syndrome (ARDS) generate heterogeneous trial populations. Non-random variation in the treatment effect of an intervention due to differences in the baseline risk of death between patients in a population represents one form of heterogeneity of treatment effect (HTE). We assessed whether HTE in two sepsis and one ARDS RCTs could explain indeterminate trial results and inform future trial design.MethodsWe assessed HTE for vasopressin, hydrocortisone and levosimendan in sepsis and simvastatin in ARDS patients, on 28-day mortality, using the total Acute Physiology And Chronic Health Evaluation II (APACHE II) score as the baseline risk measurement, comparing above (high) and below (low) the median score. Secondary risk measures were the acute physiology component of APACHE II and predicted risk of mortality using the APACHE II score. HTE was quantified both in additive (difference in risk difference (RD)) and multiplicative (ratio of relative risks (RR)) scales using estimated treatment differences from a logistic regression model with treatment risk as the interaction term.ResultsThe ratio of the odds of death in the highest APACHE II quartile was 4.9 to 7.4 times compared to the lowest quartile, across the three trials. We did not observe HTE for vasopressin, hydrocortisone and levosimendan in the two sepsis trials. In the HARP-2 trial, simvastatin reduced mortality in the low APACHE II group and increased mortality in the high APACHE II group (difference in RD = 0.34 (0.12, 0.55) (p = 0.02); ratio of RR 3.57 (1.77, 7.17) (p < 0.001). The HTE patterns were inconsistent across the secondary risk measures. The sensitivity analyses of HTE effects for vasopressin, hydrocortisone and levosimendan were consistent with the main analyses and attenuated for simvastatin.ConclusionsWe assessed HTE in three recent ICU RCTs, using multivariable baseline risk of death models. There was considerable within-trial variation in the baseline risk of death. We observed potential HTE for simvastatin in ARDS, but no evidence of HTE for vasopressin, hydrocortisone or levosimendan in the two sepsis trials. Our findings could be explained either by true lack of HTE (no benefit of vasopressin, hydrocortisone or levosimendan vs comparator for any patient subgroups) or by lack of power to detect HTE. Our results require validation using similar trial databases.

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