CI: Body Weight and Outcomes: Trauma Patients (2007)


Brown CVR, Neville AL, Rhee P, Salim A, Velmahos GC, and Demetriades D. The impact of obesity on the outcomes of 1,153 critically injured blunt trauma patients. J Trauma. 2005;59:1048-1051. 

PubMed ID: 16385276
Study Design:
Retrospective Cohort Study
B - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
The purpose of this study was to determine if obese, critically ill blunt trauma patients had increased morbidity, mortality, and length of stay when compared to similar patients in the same ICU who had BMI < 30 kg/m2).
Inclusion Criteria:
All consecutively admitted adult critically ill blunt trauma patients.
Exclusion Criteria:
Patients not admitted to trauma ICU.
Description of Study Protocol:


Database records during 5-year study period.


Retrospective cohort study

Blinding used (if applicable)


Intervention (if applicable)


Statistical Analysis

Values were reported as mean ±  SD, odds ratio, and 95% CI. Categorical variables were compared using X2 or Fisher's exact tests. Continuous variables analyzed using two-tailed Student's t test. Continuous variables such as age, BMI, injury severity score, heart rate, and systolic blood pressure were made into dichotomous variables at clinically significant cutoff points (e.g. BMI > 30; age > 55). Investigators univariately analyzed dichotomous variables and categorical variables. Any variable with a difference of p< 0.2 included in stepwise logistic regression for identification of independent risk factors for mortality. Statistical significance was p < 0.05 for all comparisons.

Data Collection Summary:

Timing of Measurements


Dependent Variables

  • Mortality (death)
  • Length of total hospital stay (days)
  • Length of ICU stay (days)
  • Length of mechanical ventilation (days)
  • Complications

Independent Variables

 Obesity (measured as BMI > 30 kg/m2)

Control Variables

Age, sex, Injury Severity Score, admission vitals, type of blunt trauma

Description of Actual Data Sample:

Initial N:

  • 1,153 blunt trauma patients admitted to ICU; included 283 obese (mean BMI = 35 ± 6 kg/m2) and 870 non-obese (mean BMI 25 ± 3 kg/m2)
  • 70 - 71% male gender

Attrition (final N): N/A

Age: adults with similar mean age (obese patients 46 ± 18; non-obese 45 ± 20)

Ethnicity: not described

Other relevant demographics:

  • Similar Injury Severity Scores (ISS) (p=.64), however, non-obese had more head injuries (p=.0001; higher Glasgow Coma Scores (GCS) (p=.004) and Abbreviated Injury Scores (AIS) (p=.03). Obese subjects had more lower extremity fractures (p<.0001) and chest injuries (p=.05) but there was NS difference in chest AIS 


  • BMI obese subjects 35 ± 6 kg/m2
  • BMI non-obese subjects 25 ± 3 kg/m2

Location: Los Angeles County/University of Southern California Medical Center

Summary of Results:

Complications in Obese and Non-Obese Patients



n = 283


n = 870

Statistical Significance of Group Difference

Any complication*

n=118 (42%)

275 (32%)


Mechanical ventilation




Length of mechanical ventilation

8 ± 14 days

6 ± 9 days 


ICU length of stay

13 ± 14 days

10 ± 10 days


Total hospital length of stay

24 ± 21 days

19 ± 17 days

p = 0.01


Obese patients suffered more infections and complications*: sepsis (p=.09); ARDS (p=.002); multi system organ failure (p=.0006); deep vein thrombosis p=.07); myocardial infarction (p=.02); any complication p=.002); NS differences for pneumonia or pulmonary embolism.

Stepwise logistic regression revealed the following as independent risk factors for mortality:

Risk Factor

Adjusted Odds Ratio

95% Confidence Interval

p value



1.0 - 2.3


Age > 55


2.32 - 4.6

< 0.0001

Admission Hypotension


2.1 - 6.6

< 0.0001

Glasgow coma scale < 8


3.6 - 7.4

< 0.0001

Injury severity score > 16


5.6 - 18.0

< 0.0001


Author Conclusion:

Obese patients sustain different injuries than their lean counterparts. The obese have more complications, especially multiple system organ failure, acute respiratory distress syndrome, myocardial infarction, and renal failure. This results in need for longer mechanical ventilation, longer ICU and hospital stays. Obesity is an independent risk factor for mortality following severe blunt trauma.

Funding Source:
University/Hospital: University of California, Harvard Medical School
Reviewer Comments:
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) Yes
  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) Yes
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? N/A
  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.) 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? Yes
  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%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  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? 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? 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? 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? 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)? 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? N/A
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