Intensive Care Outcome Network (ICON) Study

Phase 3







Little is known about the long-term physical and psychological effects of severe, critical illness in adults. This study will collect patient-reported information on long-term illness and its effect on quality of life from survivors who have been treated on Intensive Care Units (ICUs) in UK hospitals. The study will primarily use mailed questionnaires to collect the information. The results will allow better understanding of the problems these patients face, especially after they leave hospital, leading to better information for patients and carers, better treatments to minimise these problems, and better data for researchers to plan and interpret future studies.


Primary outcome measures

Data from the ICON study will allow identification of risk factors associated with poor long term outcomes for intensive care patients. Identification of these risk factors will help in the development of effective treatments and enable these risk factors to be recognised earlier. This entire process has the ultimate goal of improving the long-term quality of life of patients who have experienced treatment on an intensive care unit.


Secondary outcome measures

Detailed aims of the ICON study are:


  • To determine the health-related quality of life of patients at three, twelve and twenty-four months after ICU discharge and compare this with an age-, sex- and socio-economic status-matched historical control group.
  • To determine the number of patients at risk of developing Post Traumatic Stress Disorder (PTSD) at three, twelve and twenty-four months after ICU discharge. 
  • To determine number of patients at risk of depression and anxiety disorders at three, twelve and twenty-four months after ICU discharge.
  • To assign a health utility index value to each of the first two survivor-years to allow calculation of quality-adjusted life years (QALYs) for all patients and those in specific diagnostic groups.
  • To determine differences in health status for broad subgroups of patients based on diagnosis, and calculated (APACHE II and/or ICNARC score) hospital mortality risk.
  • To determine the survival of these patients beyond two years after hospital discharge and so determine the relative risk of death over time of all these patients compared with an age and sex matched group drawn randomly from the UK population.
  • To determine the relative risk of death over time for broad subgroups based on diagnosis, calculated hospital mortality risk (APACHE II and/or ICNARC score), sex, geography and socio-economic group (from postcodes) compared with the risk for all patients.
  • To determine the relative risk of death for patients with a similar diagnosis



The ICON study will generate data on long-term survival after critical illness, the effects of this illness on the health-related quality of life (HRQoL) and psychological morbidity, and the changes in these measurements over the first two years after discharge. 


The final benefit of the ICON study will be the resource it will create.  In future, health economists will be able to interrogate the database and generate survival data and importantly HRQoL information, and hence utility weights, for the group of ICU patients they wish to study, irrespective of whether that group is defined by diagnosis, age, sex, physiological derangement or other variables.


Study design

This is a multi-centre longitudinal observational study of survivors of critical illness.


Participants meeting the inclusion criteria will be recruited from 16 of the intensive care units in the UK.


Inclusion criteria

To be eligible to be invited to take part in the ICON study, participants must

  • have experienced at least 24 hours of level three dependency care (ICU care) at any time during their hospital stay
  • have survived until the time of hospital discharge
  • have reached at least 16 years of age on the date of admission to ICU
  • not be in prison
  • not live in residential care.


Exclusion criteria

Patients are excluded if they are:

  • aged under 16 years
  • unable to complete questionnaires and have no consultee to fill in the forms on their behalf
  • foreign nationals
  • in residential care
  • in prison
  • unwilling to consent; or
  • their life status cannot be traced (i.e. have no GP or NHS numbers).

The measurements

Patients will receive 3 sets of questionnaires at three, twelve- and twenty four months after ICU discharge. The questionnaires used are shown in the table below.




Time required †


Health-related quality of life



Health-related quality of life



Anxiety and Depression

HADS survey


PTSD symptoms




SF-36, Medical Outcomes Study Short Form 36-Item Health Survey; EQ-5D, EuroQoL instrument; HADS, Hospital Anxiety and Depression Scale; PCL-C, PTSD Civilian Checklist

† Derived from pilot testing


Sample size

The minimum target total survivor recruitment would be at least 1000 survivors per year returning the 12 month study questionnaires. 


Patient consent and study withdrawal

After discharge from the intensive care unit, but before discharge from hospital, an appointed research nurse will give a patient information leaflet to the patient.  After allowing the patient at least 24 hours in which to study the information the patient will be asked for consent to take part in the study.  If the patient gives consent, the signed consent form will be sent to the study office with the patient’s details (name, address, NHS number, hospital number, CMP number, date of birth, GP details and dates of admission and discharge to hospital and ICU).  If the patient refuses consent, the study office will be notified to prevent the office approaching the patient again.


If patients have not been approached before discharge from hospital, the patients’ details (name, address, NHS number, hospital number, CMP number, date of birth, GP details and dates of admission and discharge to hospital and ICU) will be sent to the study office so that the study office can screen the list of patients for eligible patients before writing to ask for consent.


Patients can withdraw consent to continue in the study at any point, either verbally, or in writing, or by returning a blank questionnaire. If they do so they will not receive any further mailings or telephone calls, and their data will be removed from the database.


Data protection and NIGB approval

The data collection, storage and access rights conform to the standards set out in the Data Protection Act 1998.  In addition, the National Information Governance Board has given approval for the ICON study to hold personal identifiable patient data under Section 251 of the NHS Act 2006.


Proposed duration

Patients will be followed up for a period of up to 24 months post-ICU discharge.  Sufficient data will be retained for five years to allow five year survival to be determined via NSTS/PDS.


Patients identified as at risk of psychological morbidity

Questionnaires returned will be scored according to their specific manuals.  There is the potential that patients may return questionnaires indicative of poor psychological health, in which case, provided the patient consented for the study to contact their GP, a standard letter will be sent to the patient’s GP to highlight that the patients has demonstrated significant risk of post-traumatic stress disorder (PTSD), and/or anxiety or depression on the relevant screening tools.


If the patient did not consent for a warning letter to be sent to the GP, a standard letter will be sent to the patient instead.  This letter will inform the patient that their questionnaire results were inconclusive and they are recommended to visit their GP to discuss their psychological health.


Study team

Chief Investigator: Dr J Duncan Young, Consultant Anaesthetist, Oxford University Hospitals NHS Trust.


Study Coordinator: Judith Bishop.


Contact details


Telephone: 01865 922440

Fax: 0844 3584470



ICON is funded by the BUPA Foundation.






PTSD Posttraumatic stress disorder (PTSD) is a severe anxiety disorder that can develop after exposure to any event which results in psychological trauma. Symptoms of PTSD include re-experiencing the original trauma(s) through flashbacks or nightmares, avoidance of stimuli associated with the trauma, and increased arousal – such as difficulty falling or staying asleep, anger, and being extra vigilant.


APACHE II (Acute Physiology and Chronic Health Evaluation II) is a severity-of-disease classification system, one of several ICU scoring systems. It is applied within 24 hours of admission of a patient to an intensive care unit (ICU): an integer score from 0 to 71 is computed based on several measurements; higher scores correspond to more severe disease and a higher risk of death. 

The ICNARC physiology score is a score from 0 to 100 based on weightings for deviations from normal in twelve physiological parameters during the first 24 hours in the intensive care unit.

HRQoL (Health Related Quality of Life) refers to how the individual’s wellbeing may be impacted over time by a disease, a disability, or a disorder.

SF-36 (The Short Form (36) Health Survey) is a survey of patient health. It is commonly used in health economics in determining the cost-effectiveness of a health treatment.


EQ-5D is a standardised measure of health status applicable to a wide range of health conditions and treatments. It provides a simple, generic measure of health for clinical and economic appraisal. The EQ-5D essentially consists of 2 pages - the EQ-5D descriptive system and the EQ visual analogue scale (EQ VAS).


HADS (Hospital Anxiety and Depression Scale) is a 10-point scale commonly used by doctors to determine the levels of anxiety and depression that a patient is experiencing. These points are determined by a series of questions, some geared towards anxiety, some towards depression.  The patient is asked to answer with his/her feelings during the past week. If a patient scores the lowest possible value of 1 they potentially need clinical psychiatric treatment. If the patient scores the maximum points (10) they will be considered clinically stable.


PCL-C (Post-traumatic stress (PTSD) checklist – civilian version) is a questionnaire administered to assess symptoms of post-traumatic stress amongst a civilian population.  The symptoms endorsed may not be specific to just one event, which can be helpful when assessing survivors of stressful events who have symptoms due to multiple events.