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

Citation:
Nasraway SA, Albert M, Donnelly AM, Ruthazer R, Shikora SA, Saltzman E. Morbid obesity is an independent determinant of death among surgical critically ill patients. Crit Care Med 2006; 34:964-970. PubMed ID: 16484910
 
Study Design:
retrospective cohort study
Class:
B - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To determine whether extreme obesity is an independent determinant of death among critically ill surgical patients
Inclusion Criteria:
Admission to surgical intensive care unit (SICU) between January 1998 and March 2001. Patients included those admitted for general surgery, transplantation, vascular, cardiothoracic, neurological and other assorted surgical services including orthopedics, urology, plastics, oral/maxillary/facial, otorhinolaryngology, and surgical oncology.
Exclusion Criteria:
SICU patients for whom height and weight data not available.
Description of Study Protocol:
Data was stratified according to NIH/WHO standards with extreme obesity described as BMI > 40 kg/m2. Univariate and multivariate statistical analyses were applied to a subset of patients who stayed in SICU 4 or more days in order to determine whether extreme obesity contributed to mortality.
Data Collection Summary:
Data collection took place from January 1998 to March, 2001 in the Tufts-New England Medical Center surgical intensive care unit.
Description of Actual Data Sample:

Recruitment: Comprehensive database analysis of patients admitted from January 1998 to March 2001.

Design: Retrospective cohort.

Blinding used: None

Description of study protocol: Surgical intensive care admissions were screened daily and entered into a database. Data were analyzed for all patients for whom height and weight were available. (n=1373). A subset of patients (n=406) had SICU stay of 4 or more days and these data comprised a second analysis.

Intervention: Not applicable

Statistical analysis: Statistical comparisons between extremely obese (BMI > 40) and other patients using Student’s t-test (for age), Kruskal-Wallis test (Simplified Acute Physiology Score II and MPM-24), or Fisher’s exact and chi-square tests (gender, preexisting diabetes mellitus, vasopressor use, renal failure, mechanical ventilation, mortality). Used nonparametric Kruskal-Wallis test to compare lengths of ICU stay because outcome distributions were skewed. Multivariate analyses constructed using stepwise selection process with p values for entry (p=.15) and retention (p=.10) to pick among all potential determinants of ICU mortality other than BMI. Then, BMI was added to covariate model of mortality to estimate relationship of extreme obesity and ICU mortality. In order to show the non-linear relationship between BMI and probability of death in the ICU, investigators plotted nonparametric smoothing spline based on generalized additive model where value of smoothing parameter was selected by generalized cross-validation.

Timing of measurements: Not applicable

Dependent variables: ICU mortality (measured as death in the SICU) Hospital mortality (death in hospital after discharge from SICU) Vasopressors (needed use of vasopressor therapy) Renal failure (Creatinine > 2 mg/dL) Mechanical ventilation (needed ventilator support) ICU length of stay (days in SICU) Hospital length of stay (days in hospital)

Dependent Variable: Body Mass Index

Independent Variables:

  • Illness severity (measured with Simplified Acute Physiology Score II and the Mortality Prediction Model (MPM-24))
  • BMI stratified by NIH/WHO categories; morbidly obese individuals had BMI > 40 kg/m2
  • Age
  • Gender Pre-existing diabetes mellitus

Initial n:

  • 1373 SICU patients for whom heights and weights were available (55.3% male gender;
  • Subset of 406 SICU patients had length of stay = 4 days (57.4% male gender; mean age 61.6 (± 15.5) years

Final n (attrition): Not applicable

Age:

  • Full cohort of 1373 SICU patients for whom heights and weights were available - mean age 58.5 (± 16.6) years
  • Subset of 406 SICU patients had length of stay = 4 days mean age 61.6 (± 15.5) years

Ethnicity:

  • Full cohort (n=1,373): 90.1% white
  • Subset of 406 with LOS = 4 days: 87.9% white

Other relevant demographics: Stratified by BMI"

BMI < 18.5 n=70

BMI 18.5-24.9 n=529

BMI 25-29.9  n=408

BMI 30-39.9 n=292

BMI > 40 n=94

Other Anthropometrics: not applicable

Location: Tufts-New England Medical Center

Summary of Results:

 Univariate analyses revealed that the extremely obese were significantly different from the patients with BMI < 40 kg/m2 in that they were younger (p=.001), female (p=.001), had preexisting diabetes mellitus (p=.015), were more severely ill (SAPS II p=.005 and MPM 24 p=.001) and were more likely to require vasopressors (p=.0008). ICU mortality (p=0.13), hospital mortality (p=.32) and ICU length of stay (LOS) were not greater for the morbidly obese (.27), but median hospital LOS was greater (p=.003).

In the subset of patients with ICU stay of 4 or more days, the extremely obese were significantly different from patients with BMI < 40 kg/m2 in that they were younger (p=.025, female (p=.0009), had higher ICU mortality (p=.009) and higher hospital mortality (p=.045).

Survival models of ICU mortality for patients with LOS of
≥ 4 days
   

Univariate Analyses

Multivariate Analyses

  Mortality% (n) Odds Ratio 95% CI p value Odds Ratio 95% CI p value
Overall 13.5% (55)       

BMI ≥ 40 (n=24)

BMI < 40 (n=382)

33% (8)

12% (47)

3.56 vs BMI < 40 1.4, 8.8 .0057 7.4 vs BMI < 40 2.6, 21.3 .0002

Age ≤ 55 yrs

Age 56-69 yrs

Age ≥ 70

9%

13%

18%

 1.3 (per each 10-yr increase)  1.1, 1.6 .0079  1.3 (per each 10-yr increase)  1.0, 1.6  .0288
MPM-24*   .75 (per .10 unit increase) .67, .84 <.0001 .68 (per .10-unit increase) .58, .79 .0001

*Mortality Predictive Model (prediction of estimated death after 24 hours in ICU)
Author Conclusion:
Morbid obesity (BMI = 40 kg/m2) is an independent risk factor (Odds Ratio 7.4) for death in SICU patients with LOS of 4 or more days.
Funding Source:
University/Hospital: Tufts University of Medicine
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) N/A
  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
  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
  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
  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. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? 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
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
  1.3. Were the target population and setting specified? Yes
  2. Was the selection of study subjects/patients free from bias? 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
  2.1. 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
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? 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
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
  3. Were study groups comparable? 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
  3.1. 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? 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
  3.3. 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
  3.4. 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
  3.5. 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
  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? Yes
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? 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
  4.2. 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
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.4. 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
  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. 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
  5.1. 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
  5.2. 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
  5.3. 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
  5.4. 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
  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. 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
  6.1. 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
  6.2. 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
  6.3. 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? 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
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments 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
  6.7. 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
  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. 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
  7.1. 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
  7.2. 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
  7.3. 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
  7.4. 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
  7.5. 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
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? 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. 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
  8.1. 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
  8.2. 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
  8.3. 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
  8.4. 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
  8.5. 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
  8.6. 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
  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? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? N/A
  9.1. Is there a discussion of findings? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? 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. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes
  10.2. Was the study free from apparent conflict of interest? Yes