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

Citation:

Schwann TA, Habib RH, Zacharias A, Parenteau GL, Riordan CJ, Durham SJ, Engoren M. Effects of body size on operative, intermediate, and long-term outcomes after coronary artery bypass operation. Ann Thorac Surg 2001;71:521-31.

 
Study Design:
Correlational Study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
Goal of this study was to elucidate the effects of variations in BMI on immediate and long-term post-CABG clinical outcomes. The economic impact of BMI on postoperative cost was also evaluated.
Inclusion Criteria:
Consecutive patients undergoing isolated myocardial revascularization (CABG) at St. Vincent Mercy Medical Center from July 1991 throught 1997.
Exclusion Criteria:
No exclusion was given. Consecutive patients undergoing isolated myocardial revascularization (CABG) at St. Vincent Mercy Medical Center from July 1991 throught 1997.
Description of Study Protocol:

Recruitment Consecutive patients undergoing isolated myocardial revascularization (CABG) at St. Vincent Mercy Medical Center from July 1991 throught 1997.

Design Correlational Design

Blinding used (n/a)

Intervention (n/a)

Statistical Analysis

Univariate linear and nonlinear regression analyses were used to determine which preoperative, intraoperative and postoperative variables were significantly altered in relation to BMI.  Long-term outcomes for BMI patient groups were assessed by Kaplan-Meier survival analysis.  A p-value of less than 0.05 was always used to indicate significance.

 

Data Collection Summary:

Timing of Measurements

Preoperative, operative and postoperative data were collected.

Dependent Variables

  • Operative mortality (OM) defined as in-hospital or out-of-hospital deaths within 30 days of surgery
  • Need for blood transfusion
  • Perio-OP myocardial infarction
  • Stroke,
  • Sternal wound infections
  • Cardiovascular intensive care unit (days),
  • Time on ventilator (hours)
  • Postoperative length of stay (days)
  • Total length of stay (days)

Independent Variables

  •  Body Mass Index (BMI) defined as weight/(height)2, kg/m2; using a 75% between-group overlapping scheme for consecutive decile BMI subgroups.  First patients were ranked between 1 and 3, 560 (0-100%) in terms of increasing BMI.  A total of 37 subgroups resulted from the overlapping.

 

Description of Actual Data Sample:

Initial N: 3,560 consecutive CABG patients included 2, 401 men (67%) and 1159 women (33%)

Attrition: n/a

Age: mean age ± standard deviation was 63±10 years

Ethnicity: not reported

Other relevant demographics: none

Anthropometrics BMI ranged between 16 and 58 and were distributed in near normal fashion (median, 28.6; mean 28.9).

Location: St. Vincent Mercy Medical Center, Toledo, Ohio

 

Summary of Results:
  • Operative, economic and long-term outcomes optimal in CABG patients with BMI >24≤30 kg/m2.
  • Mild obesity BMI >30 to≤34 kg/m2 does not appear to adversely affect outcomes except for a slightly higher incidence of sternal wound infections.
  • Severely obese patients BMI > 34 kg/m2 appeared to require prolonged ventilatory support and CICU stay. They also had increased incidence of sternal wound infections.
  • Operative death and serious complications were not increased in patients with BMI>34 kg/m2.
  • Long term benefits of CABG blunted in patients with BMI < 34 kg/m2 as they had significantly reduced 5-year survival rates.
  • Smallest patients with BMI ≤24 kg/m2 had the worst outcomes. This group had more operative mortality, post operative strokes, myocardial infarction and need for blood transfusions. They had reduced 2-year and 5-year survival. These patients were significantly older and had higher incidence of COPD, CHF, low ejection fraction and left main coronary disease.

 

Operative Correlates of BMI in CABG Patients by Univariate Regression Analysis
  Coefficient a   Coefficient b      
Variable SE p value SE p value R2 Power
Sternal wound infection 5.5 <0.007  2.6

<0.001 

0.77 1.0
Operative mortality 8.8 <0.0001 4.3

<0.001 

0..61 1.0
CVICU days 1.1 <0.0001 0.52 <0.0001 0.54 0.99
Ventilator hours 5.4 <0.001 2.6 <0.001 0.35 0.98
Post operative length of stay 1.1 <0.0001 0.52 <0.0001 0.54 0.99
Total length of stay 6.2 <0.004  3.0  <0.01 0.45 0.99

Patient Outcome Results

Operative mortality was noticeably lower in patients with median BMIs compared with those with low BMIs; only a small tendency for higher operative mortality was seen at the highest BMI.

Authors report a systematic and significant decrease in postoperative blood transfusions as BMI increased.  Incidence of perio-operative MI and permanent stroke was significantly greater in patients with lower BMIs, whereas sternal wound infection rates were higher in patients with BMIs greater than the median.  Postoperative renal failure, reoperation and prolonged (>24 hour) mechanical ventilation did not differ for the various BMI groups.

Direct variable costs were lowest inpatients clustered around normal BMI, with costs increasing similarly at low and high extremes.  This effect was correlated with similar BMI effects on ventilatory and ICU requirements.

Author Conclusion:

Operative outcomes were adversely affected by small body size which reflected older age. Younger age led to better outcomes in obese. Severely obese patients were the youngest but had poorest long-term (5-year) survival.

Funding Source:
University/Hospital: Saint Vincent Mercy Medical Center, Medical College of Toledo
Reviewer Comments:

The reviewers normalized BMI to compute regression equations.

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? N/A
  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? N/A
  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? N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  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%.) 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? 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? 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)? No
  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
  8.6. 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
  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. 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? ???
  9.2. Are biases and study limitations identified and discussed? ???
  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