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Co-enrollment of critically ill patients into multiple studies: patterns, predictors and consequences

Deborah Cook12*, Ellen McDonald2, Orla Smith3, Nicole Zytaruk2, Diane Heels-Ansdell2, Irene Watpool4, Tracy McArdle4, Andrea Matte3, France Clarke2, Shirley Vallance5, Simon Finfer6, Pauline Galt7, Tim Crozier7, Rob Fowler3, Yaseen Arabi8, Clive Woolfe9, Neil Orford10, Richard Hall11, Neill KJ Adhikari3, Marie-Clauide Ferland12, John Marshall3, Maureen Meade12, The PROTECT Research Coordinators, PROTECT Investigators and Canadian Critical Care Trials Group and the Australian and New Zealand Intensive Care Society Clinical Trials Group

Author Affiliations

1 Department of Medicine, McMaster University Health Sciences Center, Hamilton, ON L8N 3Z5, Canada

2 Department of Clinical Epidemiology and Biostatistics, McMaster University Health Sciences Center, Hamilton, ON L8N 3Z5, Canada

3 Interdepartmental Division of Critical Care, University of Toronto, Toronto, ON, Canada

4 Department of Critical Care, Ottawa University, Ottawa, ON, Canada

5 Intensive Care Unit, The Alfred, Melbourne, VIC, Australia

6 The George Institute for Global Health, University of Sydney, Sydney, NSW, Australia

7 Intensive Care Unit, Monash Medical Centre, Melbourne, VIC, Australia

8 Intensive Care Department, King Saud Bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia

9 Intensive Care Unit, Royal Prince Alfred Hospital, Sydney, NSW, Australia

10 Intensive Care Unit, Barwon Health, Geelong, VIC, Australia

11 Departments of Anesthesiology, Medicine, Surgery and Pharmacology, Dalhousie University, Halifax, NS, Canada

12 Intensive Care Unit, Hopital Laval, Quebec, QC, Canada

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Critical Care 2013, 17:R1  doi:10.1186/cc11917

Published: 8 January 2013



Research on co-enrollment practices and their impact are limited in the ICU setting. The objectives of this study were: 1) to describe patterns and predictors of co-enrollment of patients in a thromboprophylaxis trial, and 2) to examine the consequences of co-enrollment on clinical and trial outcomes.


In an observational analysis of an international thromboprophylaxis trial in 67 ICUs, we examined the co-enrollment of critically ill medical-surgical patients into more than one study, and examined the clinical and trial outcomes among co-enrolled and non-co-enrolled patients.


Among 3,746 patients enrolled in PROTECT (

phylaxis for
mbolism in
ritical Care
rial), 713 (19.0%) were co-enrolled in at least one other study (53.6% in a randomized trial, 37.0% in an observational study and 9.4% in both). Six factors independently associated with co-enrollment (all P < 0.001) were illness severity (odds ratio (OR) 1.35, 95% confidence interval (CI) 1.19 to 1.53 for each 10-point Acute Physiology and Chronic Health Evaluation (APACHE) II score increase), substitute decision-makers providing consent, rather than patients (OR 3.31, 2.03 to 5.41), experience of persons inviting consent (OR 2.67, 1.74 to 4.11 for persons with > 10 years' experience compared to persons with none), center size (all ORs > 10 for ICUs with > 15 beds), affiliation with trials groups (OR 5.59, 3.49 to 8.95), and main trial rather than pilot phase (all ORs > 8 for recruitment year beyond the pilot). Co-enrollment did not influence clinical or trial outcomes or risk of adverse events.


Co-enrollment was strongly associated with features of the patients, research personnel, setting and study. Co-enrollment had no impact on trial results, and appeared safe, acceptable and feasible. Transparent reporting, scholarly discourse, ethical analysis and further research are needed on the complex topic of co-enrollment during critical illness.