CI: Body Weight and Outcomes: Cardiovascular Surgery Patients (2007)

Citation:
Potapov EV, Matthias L, Anker S, Stein J, Bondy S, Naserri BA, Sodian R, Hausmann H and Hetzer R. Impact of body mass index on outcome in patients after coronary artery bypass grafting with and without valve surgery. European Heart J. 2003; 24:1933-1941.
 
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:

The purpose was threefold:

1. To identify the optimal BMI for patients who have Coronary Artery Bypass surgery.

2. To identify the BMI that places patients at risk for adverse outcomes.

3. To identify the BMI that places patients at risk for 30 day mortality after coronary artery bypass surgery.

Inclusion Criteria:
All patients whose data was in the Deutsches Herzzentrum Berlin hospital data base, who underwent cornorary artery bypass grafting with or with out concomitant valve surgery between January 1, 1990 and December 31, 2001
Exclusion Criteria:

Patients not in the database.

Description of Study Protocol:

Recruitment : n/a (database review)

Design: retrospective cohort

Review of a large data set of cornary artery bypass grafting patients (N=22,666). Multiple preoperative and intraoperative variables, and BMI were used as covariates.  Additionally patients were divided into 20 BMI groups.  Odds ratios were calculated for complications of re-intubation, infection, re-exploration, prolonged stay (>1day) in Intensive Care and 30 day mortality.  These were adjusted for age, gender and type of surgery.

Blinding used (if applicable)

 N/A

Intervention (if applicable)

 N/A

Statistical Analysis

Statistical analyses were performed using SPSS 10.0 for Windows (SPSS Inc. Chicago,IL)

The continous variables are presented as mean ±  standard deviation. 

A multivariate logististic regression model with stepwise backward elimination procedure was used to calculate the impact of pre- and intraoperative parameters on outcomes.

The significance was set at 0.01

The change in BMI over time was assessed using ANOVA test. The year was included as a continous variable.

Odds Ratios for BMI were calculated by:

  • dividing the patients into 20 BMI groups with increments of one point between 18 and 36.
    • all patients with BMI <18 were placed in one group
    • all patients with BMI > 36 were placed in one group
  • for each end point the group with the lowest risk was identified, and set as a reference category for the calculation of Odds Ratios.
  • Calculations of Odds Ratios were adjusted for age,gender, and type of surgery.

Additional analyses:

  • all patients were divided into BMI quintiles.
  • pre-operative and postoperative parameters in these quintiles were compared using ANOVA for continous and the x2 test for categorical variables.
  • multiple comparisons were adjusted using the Scheffe' and Bonferroni-Holm methods respectively
  • significance was set at 0.01
Data Collection Summary:

Timing of Measurements

 N/A

Dependent Variables

  • Recorded re-intubation
  • Recorded re-exploration (reopening the chest during the first 7 days for bleeding)
  • Infection (deep sternal or deep leg wound infection requiring re-surgery, pneumonia, empyema, endocarditis or septsis) 
  • Prolonged LOS in the ICU (longer than 24 hours)
  • 30 day mortality (death within 30 days of admission)

Independent Variables

Weight: divided into quintiles with all patients with BMI under 18 in one group and all patients with BMI over 36 in one group. 

Control Variables

 None

Description of Actual Data Sample:

Initial N: (e.g., 22,666 (72.4% males, )

Attrition: n/a

Age: mean 63.2 ± 10.3

Ethnicity: Not given

Other relevant demographics:

  • Previous MI 54.3%
  • Previous Cardiac Surgery 8.7%
  • Left Ventricular Ejection Fraction (LVEF) 54.31% ± 8.8%
  • Hypertension 68.4%
  • Diabetes Mellitus 31.1%
  • COPD 14.8%
  • Preoperative dialysis 2.3%
  • Elective Surgery 75.5%
  • Urgent surgery 14.5%
  • Emergency Surgery 10%
  • Patients received CABG alone 76.6%
  • CABG with additional AV surgery 18.5%
  • CABG with additional MV surgery 4.8%
  • Aortic cross- clamp time (min) 50 +/- 23
  • Bypass time (min)  108.2+/- 62

Anthropometrics

quintile BMI
1
≤ 23.5
2 23.6-25.3
3 25.4-27.1
4 27.2-29.4
5
≥ 29.5

Location:

 Berlin,Germany

Summary of Results:

Outcomes in Total Study Population and by Quintiles

 

Dependent Variables Valid Cases Total

1st Quintile

2nd Quintile 3rd Quintile 4th Quintile 5th Quintile
     

BMI

      < 23.5 23.6-25.3 25.4-27.1 27.2-29.4 > 29.5
Re-intubation,(%) 22,665 3.3 4.6 b 3.3 a 2.5 a 3.1 a 3.2 a
Re-exploration,(%) 19,348 7.1 9.2 b 7.8 b,c 6.6 a,c 6 a 5.8 a
Infection Rate,(%) 22,666 10.3 11.4 c,d 9.6 a,b 8.3 a 10.3 b,c 12.2 d
Prolonged ICU stay(>1day) 22,421 27.4 33.3 e 27.4 c 24.8 d 24.4 b 27.6 d
Overall 30-day mortality (%) 22,666 5.1 7.5 c 5.6 b 4.3 a 4.2 a 3.5 a

a, b, c, d, e Different superscript letters indicate significant differences between quintiles at P< 0.01. For example, there is no significant difference in mortality between 3rd, 4th and 5th quintiles. However, 2nd and 1st quintiles are significantly different from each other and from the 3rd, 4th and 5th quintiles.

Multivariate Analyses

 

Odds Ratios (95% Confidence Intervals)

 

Re-Intubation

Re-Exploration

Infection

LOS > 1 day

30-day mortality

Age

1.038 (1.029-1.048)

1.010 (1.004 - 1.017)

1.034 (1.029 - 1.040)

1.031 (1.027 - 1.035)

1.033 (1.023 - 1.042)

Male Gender

1.340 (1.112 - 1.614)

0.812 (0.697 - 0.946)

 -

 1.179 (1.088 - 1.278)

 -

Previous MI

 -

1.186 (1.028 - 1.368) 

 -

 -

1.600 (1.294 - 1.979) 

Previous Cardiac Surgery

1.766 (1.388 - 2.248) 

 -

1.480 (1.268 - 1.728) 

1.630 (1.452 - 1.829) 

 2.32 (1.609-2.566)

BMI*

-

0.999 (0.999 - 1.000)

1.001 (1.001 - 1.001)

1.000 (1.000 - 1.000)

-

Aortic Valve Surgery

1.335 (1.076-1.656) 

1.869 (1.571-2.222) 

 1.455 (1.279 - 1.655)

11.727 (1.575-1.894) 

 2.977 (2.357-3.761)

Mitral Valve Surgery

 2.947 (1.402-2.705)

2.342 (1.794-3.056) 

2.123 (1.717-2.625) 

2.896 (2.380-2.900) 

3.848 (3.100-4.776) 

*Authors found analysis of BMI as a continuous variable inappropriate for risk stratification in cardiac surgery.

 

Author Conclusion:

Patients with low BMI (<20) are at higher risk for postoperative complications after surgery than normal or severely obese patients.

Obesity (BMI ≥ 36) is not a risk for adverse outcome except for infection.

 

Funding Source:
Reviewer Comments:

Weaknesses:

1. Operative procedures were performed by a number of surgeons using different operative techniques. 

2. The study took place at one center over 12 years, changes in techniques over that time may have impacted the study.

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
  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
  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) 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. 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.) N/A
  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
  3.4. 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
  3.5. 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
  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. Was method of handling withdrawals described? N/A
  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%.) 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
  4.3. 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? 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
  5.1. 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? 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
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  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
  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? 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? 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? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.1. 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