CI: Body Weight and Outcomes: Mixed ICU Patients (2007)

Bercault N, Boulain T, Kuteifan K, Wolf M, Runge I and Fleury J-C. Obesity-related excess mortality rate in an adult intensive care unit: a risk-adjusted matched cohort study. Crit Care Med 2004; 32:998-1003. PubMed ID: 15071392
Study Design:
Retrospective Cohort Study
B - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To determine the influence of obesity on outcomes in mechanically ventilated medical and surgical patients in the ICU.
Inclusion Criteria:

Older than 16 years

Mechanically ventilated > 48 hours

Normal weight 18.5>BMI <24.9 or obese with BMI > 30
Exclusion Criteria:

Younger than 16 years

Mechanically ventilated < 48 hours

Fluid retention (ascites or peripartum state) that artificially increased BMI

Thin BMI < 18.5 or overweight with 25>BMI<29.9
Description of Study Protocol:

Heights and weights were measured at ICU admission. Obese (case) patients were computer matched with a non-obese (control) patients according to eight criteria that included same 1) cause of admission (medical pathology or trauma); 2) indication for mechanical ventilation; 3) immunologic status; 4) cardiac status; 5) probability of death as calculated from admission SAPS II; 6) age ± 7 yrs, 7) gender; 8) status regarding acquisition of at least one severe event (resuscitated cardiac arrest, acute respiratory distress syndrome, septic shock and ICU-acquired infections.

Recruitment all patients in combined medical and surgical ICU that met requirements

 Design case-control

 Blinding used (not applicable)

 Intervention (notapplicable)

 Statistical Analysis

 Mortality rate compared by univariate analysis and then adjusted for other confounders by multivariate analysis using conditional logistic regression.

Data Collection Summary:

Timing of Measurements (not applicable)


Dependent Variables

  • mortality: death

  • ICU-acquired infection: ventilator-associated pneumonia, bloodstream infection, deep surgical wound infection (defined according to Centers for Disease Control criteria

Independent Variables: BMI


Description of Actual Data Sample:


Initial N: From a pool of 1,287 mechanically ventilated adult patients, there were 181 obese patients (BMI 36 ± 5 kg/m2)  and 586 patients with ideal BMI (BMI 22 ± 2 kg/m2). 170 pairs (64% male gender); 170 obese patients were successfully matched with 170 non obese patients.

Attrition (final N): same

Age: 65 ± 12 years

Ethnicity: not described

Other relevant demographics: pairs were matched per BMI, age, gender, cause of admission, indication for ventilation support, immunologic status, cardiac status, probability of death  measured by SAPS II (43 ± 14), status regarding acquision of at least one severe event.

Anthropometrics (pairs were matched)

Location: 18-bed medical and surgical ICU in France


Summary of Results:

Obesity was an independent risk factor for ICU death (OR, 2.1; 95% CI, 1.2-3.6; p = .007) in the whole group. In younger subjects (< 65 years with mean age 52 ± 10 years), obesity remained associated with ICU mortality rate (OR, 2.5; 95% CI, 1.1-6.1; p = 0.03)

Obese patients suffered significantly more septic shock and acquired infections than matched nonobese patiients (OR,4; 95% CI, 1.4-11.8; p=.01).



Author Conclusion:
Obesity is an independent risk factor for intensive cqre unit death and should be regarded as a severe comorbidity.
Funding Source:
Reviewer Comments:
Matching of obese (case) and non obese (control) subjects was very elaborate and done by a computer.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) N/A
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) N/A
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) Yes
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? Yes
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.6. Was clinical significance as well as statistical significance reported? N/A
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes