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Informed consent in clinical trials in critical care: experience from the PAC-Man Study

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To identify the proportion of critically ill patients able to consent to participation in a randomised controlled trial (RCT) and to assess to what extent patient consent and relative assent processes could be conducted according to ethics committee permissions.


Descriptive study nested in an RCT.


Fifty-six UK intensive care units participating in the PAC-Man trial.

Patients and participants

First 500 patients consecutively enrolled into PAC-Man.

Measurement and results

The outcome measures were patient consent and/or relative assent. Of the 498 patients included, 13 (2.6%) provided consent before randomisation. Of the remaining 485 patients, relative assent was obtained for 394 patients (81.2%), and refused post-randomisation for 3 patients (0.6%). No relatives were available for 15 patients (3.1%), and it was unclear from documentation whether relative assent had been obtained for 73 patients (15.1%). Of the 482 patients who did not provide consent prior to randomisation, 188 (39%) survived. Of these, 175 (93.1%) gave retrospective informed consent, six (3.2%) refused, and seven (3.7%) did not regain mental competency.


A very small proportion of patients were able to give consent before randomisation. Due to the high in-hospital mortality (60.6%), only around one third of the remaining patients could provide consent retrospectively. This study demonstrates difficulties experienced in obtaining consent from critically ill patients to participate in medical research and raises important issues about the ethical basis of the consent process in critical care.

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We wish to thank the patients and staff at participating hospitals and the PAC-Man Study Steering Committee, and David Harrison for extra analyses. We also wish to thank Lesley Morgan (Trial Manager for the TracMan Trial) and Ian Roberts (Principal Investigator for the CRASH Trial) for their helpful comments.

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Authors and Affiliations


Corresponding author

Correspondence to Diana Elbourne.

Additional information

Funding: The PAC-Man trial (HTA Project No. 97/08/03) was funded by the UK National Health Service Research & Development Health Technology Assessment Programme. (Disclaimer: The views and opinions expressed in this article do not necessarily reflect those of the National Co-ordinating Centre for Health Technology Assessment.) The NHS Research & Development Health Technology Assessment Programme had no involvement in the design, conduct and analysis of the study.

Contributors: S.E. Harvey conceived and designed the study and participated in the analysis and interpretation of data and in writing the paper. D. Elbourne participated in the analysis and interpretation of data and in writing the paper. J. Ashcroft and C.M. Jones collected the data and participated in the interpretation of data and in writing the paper. K. Rowan conceived and designed the study and participated in the interpretation of data and in writing the paper. S.E. Harvey is the guarantor of the paper and accepts full responsibility for the conduct of the study, had access to the data, and controlled the decision to publish.

Competing interest statement: All authors declare no conflict of interest.

Ethics approval: The PAC-Man trial (Application reference number MREC/00/2/83) was approved by the North Thames Multi-centre Research Ethics Committee on 12 March 2001, as well as all relevant Local Research Ethics Committees, and Research & Development Departments at collaborating hospitals.

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The authors wrote this article on behalf of the PAC-Man Study Collaboration

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Harvey, S.E., Elbourne, D., Ashcroft, J. et al. Informed consent in clinical trials in critical care: experience from the PAC-Man Study. Intensive Care Med 32, 2020–2025 (2006).

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