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EuSOS: European Surgical Outcomes Study

Pearse, Rupert M; Rhodes, Andrew; Moreno, Rui; Pelosi, Paolo; Spies, Claudia; Vallet, Benoit; Metnitz, Philip; Bauer, Peter; Vincent, Jean-Louis

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European Journal of Anaesthesiology: June 2011 - Volume 28 - Issue 6 - p 454-456
doi: 10.1097/EJA.0b013e328344907b
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Complications following major surgery are a leading cause of morbidity and mortality,1–5 although in surgical patients in general, the incidences of post-operative complications and death are low. However, studies from the UK suggest that a readily identified high-risk sub-group accounts for over 80% of post-operative deaths, but less than 15% of in-patient procedures.4,5 Each year in the UK, 170 000 patients undergo high-risk non-cardiac surgery, of whom 100 000 will develop complications resulting in over 25 000 deaths.4–6 Patients who develop complications but survive will still suffer reductions in functional independence and a substantial decrease in medium and long-term survival.1–3 Advanced age, co-morbid disease, major and urgent surgery are the key factors associated with increased risk.4–6 Despite strong evidence of the impact of poor surgical outcomes, our understanding of standards of care for patients undergoing major surgery is limited. Particularly, little is known about the availability of critical care resources for non-cardiac surgical patients and the impact of critical care admission on clinical outcomes. Importantly, survival among patients who develop post-operative complications varies widely between hospitals, confirming both the potential and the need to improve clinical outcomes in this group.7

Recent developments in peri-operative critical care may improve outcomes significantly for high-risk non-cardiac patients, but it is not clear whether the supply of critical care facilities is sufficient to meet the demands of high-risk surgical patients. Recent studies have demonstrated that fewer than one third of UK high-risk non-cardiac surgical patients are admitted to critical care following surgery.4,5 Those patients who did receive this level of care were discharged after a median stay of 24 h and subsequently lingered for many days on standard surgical wards. This situation contrasts starkly with peri-operative care for cardiac surgical patients for whom post-operative critical care admission is routine. Cardiac surgical patients also have a high incidence of co-existing disease and undergo major surgery, but with an overall mortality rate as low as 2%.8,9

At present, we have little data on current standards of care for patients undergoing major non-cardiac surgery across Europe, or the clinical outcomes following such procedures. Such data would significantly improve our understanding of poor surgical outcomes and how these relate to standards of clinical care. This in turn would allow us to focus research efforts on addressing important areas of uncertainty in patient care. A rigorous, prospective evaluation of standards of peri-operative care across Europe would provide important data which could trigger a step change in the current approach to care of the patient undergoing major non-cardiac surgery.

Research questions

  1. What is the in-hospital mortality rate for patients undergoing non-cardiac surgery in Europe?
  2. What is the duration of hospital stay for patients undergoing non-cardiac surgery in Europe?
  3. What is the current standard of peri-operative critical care provision for patients undergoing non-cardiac surgery in Europe?
  4. What is the current standard of haemodynamic (cardiac output) monitoring for patients undergoing non-cardiac surgery in Europe?
  5. Is there any evidence of differences in the standard of peri-operative care provision for patients undergoing non-cardiac surgery in different healthcare systems within Europe?
  6. Is there any evidence of differences in hospital stay and mortality for patients undergoing major non-cardiac surgery in different healthcare systems within Europe?
  7. What factors determine planned and unplanned admission to critical care after surgery?
  8. Are the factors associated with critical care admission similar to those associated with post-operative death?

Study design

This international cohort study of all adult patients undergoing in-patient non-cardiac surgery will recruit patients within a 7-day period in April 2011.

Inclusion and exclusion criteria

Recruitment will include consecutive patients admitted to participating centres undergoing elective and non-elective non-cardiac surgery with a planned overnight stay during the 7-day study period. Patients undergoing planned day-case surgery, cardio-thoracic surgery, neurosurgery, radiological or obstetric procedures will be excluded. All eligible patients undergoing surgery within the 7-day study period will be recruited wherever possible.

Participating centres

We aim to recruit in as many European centres as possible, but anticipate that a minimum of 150 centres in ten or more nations will be required.

Ethical considerations

National coordinators will be responsible for clarifying the need for ethics approval and applying for this wherever appropriate. We expect that in most, if not every participating country, there will be no requirement for individual patient consent as all data are already recorded as part of routine clinical care and will be anonymised.

Data collection

Data will be collected describing all eligible patients undergoing surgery within the 7-day recruitment period. These patients will then be followed-up until hospital discharge. Data will then be pseudo-anonymised (coded) and transcribed by local investigators onto an internet-based electronic case record form. A centre-specific form will be completed once for each hospital to provide data including secondary/tertiary centre, number of operating rooms, number and level of critical care beds, among others.


An operating room datasheet will be completed once for each patient recruited to include patient factors (age, sex, American Society of Anesthesiologists physical status, major co-morbid disease, etc.), surgical factors (procedure category, grade and urgency of surgery, grade of surgeon, surgical checklist, etc.), anaesthetic factors (anaesthetic technique, haemodynamic monitoring, airway, grade of anaesthetist, etc.), post-operative care (post-operative recovery ward stay, post-operative invasive or non-invasive ventilation or inotrope within first 24 h). A critical care datasheet will be completed once for each patient admitted to critical care at any time after surgery, including whether admission was planned or unplanned (organ support, simplified acute physiology score III, sequential organ failure assessment score, etc.). Patients will be followed until death or hospital discharge for the following outcomes: duration of critical care stay, critical care mortality, duration of hospital stay and in-hospital mortality.

Statistical analysis

The data will be collected as part of routine clinical care. Categorical variables will be presented as proportions and will be compared using χ2-test or Fisher's exact test. Continuous variables will be given as mean (SD) if normally distributed or median (inter-quartile range) if not normally distributed. Comparisons of continuous variables will be performed using one-way analysis of variance or Mann–Whitney U-test as appropriate. Univariate analysis will be performed to test factors associated with planned and unplanned admission to critical care and/or in-hospital death. A multiple logistic regression model will be used to identify independent risk factors. A stepwise approach will be used to enter new terms into the logistic regression model in which P-value less than 0.05 was set as the limit for inclusion of new terms. A logistic regression model will be performed to assess independent association between prognostic factors and outcomes. Results of logistic regression will be reported as adjusted odds ratios with 95% confidence intervals. A single final analysis is planned at the end of the study.

Outcome measures

Primary outcome measures are as follows:

  1. In-hospital mortality.

Secondary outcome measures are as follows:

  1. Duration of hospital stay.
  2. Planned admission to critical care.
  3. Unplanned admission to critical care.
  4. Duration of critical care stay.

Sample size calculation

We anticipate that approximately 20 000 patients will be required to provide a sample of up to 2000 admissions to critical care after surgery. Assuming an overall mortality rate following surgery of 1%, a sample size of 20 000 patients will yield 200 deaths. This will allow the inclusion of at least 15 variables in a logistic regression model for mortality. The rate of admission to critical care is likely to vary between nations, but an overall rate of 10% will yield data from up to 2000 admissions to critical care, whereas an overall rate of 5% will yield 1000 admissions. This should allow construction of a robust logistic regression model for this outcome. Twenty thousand patients will also provide more than 99% confidence for the overall mortality rate with 0.37% confidence width. If 200 deaths are observed in an overall sample of 20 000 patients, the 99% confidence interval for the proportion would be 0.008–0.012 with a confidence width of 0.37%. This dataset would also have sufficient generalisability to inform the practice of peri-operative care on an international basis.


The study will be conducted by the European Surgical Outcomes Study (EuSOS) study group on behalf of the European Society of Intensive Care Medicine and the European Society of Anaesthesiology. National coordinators will lead the project within individual nations and identify participating hospitals, translate study paperwork, distribute study paperwork and ensure necessary regulatory approvals are in place. Local coordinators will lead in the EuSOS study in individual institutions ensuring all relevant regulatory approvals are in place and adequate training of staff. They will supervise data collection, ensure timely data return and act as guarantor for the integrity and quality of data collected.

Time scale

  1. August–December 2010: finalise case record form, reverse translate protocol, secure regulatory approvals, build internet-based data portal and recruit sites.
  2. January–March 2011: test internet-based data portal, recruit sites, circulate information resources to participating sites.
  3. April 2011: 7-day recruitment period, patient follow-up, internet-based data return.
  4. May–June 2011: finalise patient follow-up, complete internet-based data return.
  5. July–September 2011: data checks, verification and analysis.
  6. October–December 2011: commence dissemination of findings.


Funding: the EuSOS study is funded and supported by the European Society of Anaesthesiology and the European Society of Intensive Care Medicine. In addition, R.M.P. is a National Institute for Health Research (UK) clinician scientist.

Trial registration:, identifier NCT01203605.


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© 2011 European Society of Anaesthesiology