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


Byrnes M, McDaniel M, Moore M, Helmer S and Smith R. The effect of obesity on outcomes among injured patients. J Trauma 2005; 58:232-237.

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 evaluate the effect of obesity on morbidity, mortality and patterns of injury among adult trauma patients.
Inclusion Criteria:
  • ages 18 years or older admitted to level I trauma center
Exclusion Criteria:
  • < 18 years
  • no height and weight available from medical record
Description of Study Protocol:

Recruitment - retrospective - reviewed data for all eligible patients

Design - retrospective cohort study

Blinding used - not applicable

Intervention - not applicable

 Statistical Analysis

  • Student's t-test for continuous data
  • chi square analysis with Yates correction for categorical data
  • P value significance set a priori at < 0.05
Data Collection Summary:

Timing of Measurements

  • not applicable

Dependent Variables

  • mortality (death from all causes)
  • mortality from pulmonary complications 
  • pulmonary complications (pneumonia, ARDS or required mechanical ventilation)
  • renal complications (acute renal insufficiency and acute renal failure)
  • cardiovascular complications (myocardial infarction, arrhythmias requiring tratment and hypotension requiring vasoactive medications)

Independent Variables

  •  Body mass index


Description of Actual Data Sample:


Initial N: 1179 patients for whom height and weight were available

  • BMI < 35 were 67% male;
  • patients with BMI ≥ 35 were 56.6% male

Attrition (final N): N/A

Age:  BMI < 35 mean age 43.8; BMI ≥ 35 mean age 46.1 (p=0.03)

Ethnicity: not described

Other relevant demographics: patients with BMI ≥ 35 were significantly more likely to be hypertensive (p<0.0001), have diabetes mellitus (p<0.001), or be injured in a motor vehicle crash. Obese and lean patients had similar injury patterns. There were NS differences in the cohorts with respect to blunt injury, trauma level, injury differences in the cohorts with respect to blunt injury, trauma level, injury severity score (ISS) or Glasgow coma score (GCS).

Anthropometrics (e.g., were groups same or different on important measures)

Location: University of Kansas School of Medicine - Wichita, KS


Summary of Results:

Mortality and renal complications were significantly increased among patients with BMI ≥ 35.


BMI < 35


BMI ≥ 35



Statistical Significance of Group Difference

(p value)

Total sample size




Total mortality




Mortality with ISS ≥ 15




Mortality with ISS ≥ 20




Mortality on ventilator




Pulmonary complications**




Renal complications




Renal complications ISS
≥ 15




Renal complications ISS
≥ 20




Cardiovascular complications**




Length of Stay

4.7 days

7 days


ICU Length of Stay

6.1 days

8.7 days


Required mechanical ventilation




 ** not significantly related to ISS score when stratfied by ISS

Other Findings


Author Conclusion:
Obese patients were 2.8 times more likely to die after being injured than patients with BMI < 35.
Funding Source:
University/Hospital: Via Christi Regional Medical Center, University of Kansas
Reviewer Comments:
The paper included a good discussion with limitations of the study. One third of eligible patients had to be excluded because the medical record lacked height and weight information needed to calculate BMI.
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) 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.) N/A
  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? N/A
  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? 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? 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)? No
  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