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

Tremblay A, Bandi V. Impact of body mass index on outcomes following critical care. Chest. 2003; 123(4):1202-1207.
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 impact of BMI on outcomes for critically ill hospitalized patients.

Outcomes were defined as:

In hospital mortality

Functional status at time of discharge from the ICU

LOS following ICU admission

Inclusion Criteria:
All patients from large multi-institutional critical care patient data set
Exclusion Criteria:

Patients in data base that did not have one of the following:

Admission height

Admission weight

and Patients in the data base that did not have at least one of the following:

SAPSII ( Simplified Acute Physiologic Score) or MPM (Mortality Prediction Model)



Description of Study Protocol:


 Patients from the Project Impact Critical Care Data System;Society of Critical Care Medicine;Des Plaines, IL. Entire patient data base was queried


 Data was collected prospectively by dedicated data cooridinators.  Patients were assigned to  two cohort groups based on the availability of the severity of illness scores. Either SAPS-II or MAP-O.  The normal BMI group was the control grol group.  All BMI groups were compared to the normal BMI group. Hospital survival and functional status for each BMI group were calculated according to quartiles of SAPS-II scores or MPM-O scores. 

Blinding used (if applicable)


Intervention (if applicable)


Statistical Analysis

 The groups were compared with the x2 test and  Bonferroni correction for multiple comparison between groups. 

Hospital LOS and ICU LOS for survivors in each BMI group according to quartiles of SAPS-II or MPM-O scores were compared with the Kruskal-Wallis H test followed by the Dunnett t test for multiplw comparisons against a single control group.

Logistic regression was done to assess the combiled impact of age, gender, type of ICU admission, BMI group, and severity score for survival and functional status.

Area under the receiver operating curve (AUC), model x2 test and Hosmer-Lemeshow goddness-of-fit statistics were used to select the best model. 

Cox regression models was used for the LOS data censoring at the time of death to avoid a positive effect on LOS from early mortality. A p value of <0.05 was accepted as being statistically significant.

Data Collection Summary:

Timing of Measurements


Dependent Variables

  • Variable 1: Underwieght = BMI <20
  • Variable 2: Over weight = BMI 25-30
  • Variable 3: Obese = BMI 30-40
  • Variable 4: Severe Obesity = BMI >40

Independent Variables

 SAPS-II score and MPM-O score

Control Variables

 Normal BMI Defined as 20

Description of Actual Data Sample:


Initial N:  63,646; 55.8% male

Attrition (final N):    41011; 54.4-54.7% male

Age: 60.1  (18.6)

Ethnicity: Not given

Other relevant demographics: Hospital admission type ie 61.5% medical, 12.2% emergent surgical, 26.2% elective surgical

Anthropometrics (e.g., were groups same or different on important measures) Only BMI was provided


 Multi institutional data from IL. data base

Summary of Results:



Mortality   95% Confidence Interval

Underweight 1.19 1.26
Overweight 0.92 0.89
Obese 0.96 0.93
Severely Obese 1.09 1.03


LOS                                        ICU



Underweight 0.96 0.94
Obese 0.96 not significant
Severely Obese 0.81 0.84

 LOS Hospital


Underweight 0.91 0.90
Obese 0.96 not significant
Severly Obese 0.83 0.87

Disability At Discharge

Underweight 1.11 1.19
Overweight 0.93 0.94
Obese 0.94 0.91
Severely Obese 1.09 1.02

Other Findings

 There was no increased risk of mortality in obese or severely obese patients even when the patients who were over 65 years were analyzed seperately


Author Conclusion:

The most important effects of BMI on the outcomes were seen in the underweight group. This group had increased chance of mortality and was significantly less likely to return to their preadmission functional status.  The increased mortality was seen in the medical and emergent sergical groups but not in the elective surgery group.

Increased hospital LOS and ICU LOS was seen in the severely obese group and to a lesser degree in the underweight group.  Since there was lack of evidence showing increased mortality for the severely obese group the  longer LOS could be attributed to prolonged recovery from illness or to the increased incidence of nonfatal complications.

Overweight and obese patients may have more favorable outcomes in terms of mortality ond hospital discharge functional status

Funding Source:
University/Hospital: Baylor College of Medicine
Reviewer Comments:

The large sample size from multiple hospitals may make the data more reliable than smaller studies.  However, one must be cautious because the original query did not look at specific diagnoses. The diagnosis could have impacted the BMI group the patient fell into.  IE patients with recent weight loss or chronic underlying illness such as cancer, HIV etc may influence both weight and mortality.

Also, it should be noted that ICU height and weight may have been estimated rather than actually measured thus making the BMI data inaccurate.

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) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  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.) N/A
  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? N/A
  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? ???
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  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? N/A
  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? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? No
  6.6. Were extra or unplanned treatments described? No
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  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? N/A
  7.2. Were nutrition measures appropriate to question and outcomes of concern? N/A
  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)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  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? No
  10.2. Was the study free from apparent conflict of interest? Yes