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

Citation:

Engelman DT, Adams DH, Byrne JG, Aranki SF, Collins JJ, Couper GS, Allred EN, Cohn LH, Rizzo RJ. Impact of body mass index and albumin on morbidity and mortality after cardiac surgery. J Thorac Cardiovasc Surg 1999;118:866-873.

 
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:
1. To assess the contribution of BMI to morbidity and mortality after cardiac surgery
2. To determine the degree to which hypoalbuminemia contributed to postoperative morbidity and mortality
3. To assess the association between BMI and surgical outcome and preoperative nutritional status
Inclusion Criteria:
1. Patients undergoing CABG and/or valve surgery at Brigham and Women's Hospital between 1993 and 1997
2. Patients undergoing primary as well as reoperative surgery
Exclusion Criteria:
Patients with other concomitant surgical procedures such as carotid endarterectomy, aortic procedures, transplantation, transmyocardial laser procedures and congenital anomalies.
Description of Study Protocol:

Recruitment

Data were collected from 5,168 consecutive patients undergoing CABG and/or valve surgery at Brigham and Women's Hospital between 1993 and 1997. 

Design

Retrospective, nonconcurrent, non-randomized 

Blinding used (if applicable)

Not discussed

Intervention (if applicable)

No intervention 

Statistical Analysis

1. X2 test was used to evaluate potential confounders of the relationship between low serum albumin or the extremes of BMI an operative morbidity and mortality. A variable was considered a potential confounder if it was related to albumin or BMI and operative death or complication with a P value of < 0.20.

2. To adjust for the potential confounding effects of other risk facotrs, multivariable logistic regression was used to evaluate operative mortality and morbidity risk associated with low albumin levels and the extremes of BMI. Potential confounders included age, sex, ejection fraction, New York Heart Association functional class, previous cardiac operation, preoperative diabetes, peripheral and cerebral vascular disease, HTN, renal failure, CHF, MI, COPD, smoking, urgency of operation, use of an internal thoracic artery and type of operation.

3. OR for mortality was calculated for each risk factor.

4. Also fit multivariable models with albumin as a continuous variable and with BMI expressed with linear and then cubic splines. Goodness of fit was assessed with the Hosmer and Lemeshow goodness-of-fit Xtest and by plotting the Hosmer and Lemeshow influence statistics and leverage against the predicted probability or death or morbidity.

Data Collection Summary:

Timing of Measurements

Data collected prospectively from 5,168 consecutive patients.

Dependent Variables

  • postoperative mortality - defined as death during the initial hospitalization or within 30 days of the operation
  • postoperative morbidity
    • CVA/TIA - verified by CT scanning and a neurologic consultation
    • renal failure
    • pneumonia
    • sepsis
    • MI
    • low cardiac output - defined as the need for an intra-aortic balloon pump or inotropic agents to keep the cardiac indes more than 2.0 L/min/m2 for > 24 hrs after surgery
    • new atrial fibrillation
    • re-exploration for bleeding
    • deep sternal wound infection
    • leg infection
    • ICU > 3 days
    • ventilatory support > 1 day
    • LOS > 10 days

Independent Variables

  • BMI (kg/m2)
    • high risk thin group defined as BMI < 20
    • high risk obese group defined as BMI > 30
  • nutritional status - determined by preoperative serum albumin
  • cardiac surgery - CABG, valve surgery or both CABG/valve surgery

Control Variables

  • age
  • sex
  • ejection fraction
  • New York Heart Association functional class
  • previous cardiac operation
  • preoperative diabetes
  • peripheral and cerebral vascular disease
    • PVD defined by history of claudication or prior peripheral bypass for occlusive arterial disease
    • CVD defined as previous CVA, TIA or carotid stenosis
  • HTN
  • renal failure
  • MI
  • COPD
  • urgency of operation
    • emergent/urgent: surgery performed within 24 hr of disease diagnosis
  • use of an internal thoracic artery
  • type of operation
Description of Actual Data Sample:

Preoperative demographics, risk factors and clinical presentation of the study group

 

    Albumin     BMI     operative death
  <2.5 2.5-3.5 >3.5 <20 20-30 >30 all patients yes no
No. patients  768 1910
2490
237
3731
1200
5168
196
4972
% patients
15
37
48

72
23
100
3.8
96.2
Demographics:                  
% female
40
32
30
60
29
36
32
42
31
% male
60
68
70
40
71
64
68
58
69
% age > 75 y
27
23
23
42
25
16
25
40
23
BMI:
                 
% <20 (thin)
6
5
4
      5
12
4
% 20-30
77
73
71
      72
65
73
% >30 (obese)
17
22
25
      23
23
23
Low serum albumin:
                 
% <2.5
      21
16
11
15
29
14
% 2.5-3.5
      21
20
 19
37
16
20
% >3.5
      58
64
70
48
55
66
Risk Factors:
                 
% EF <30%
7
7
8
14
7
6
7
16
20
% NYHA functional class IV
21
17
17
20 
18
16
18
36
17
% previous cardiac surg
17
16
16
23
16
14
16
36
15
% diabetes
30
26
28
16
24
40
28
34
27
% PVD
17
13
11
16
13
11
3
29
12
% cerebral vasc disease
16
12
10
15
12
9
11
23 
11
% HTN 61
60
57
44
57
66
58
70
58
% Renal failure
12
10
8
15
9
8
9
22
9
 % CHF
40
32
35
61
34
32
35
 57
34
 % previous MI
55
51
47
37
49
52
49
67
49
 % COPD
11
10
10
17
10
11
10
15
10
% smoking Hx
63
64
64
58
63
67
64
64
64
Clinical presentation:
                 
 % elective
58
66
70
63
67
67
67
41
68
% emergency or urgent
42
34
30
37
33
33
33
59
32
Intraoperative procedure:
                 
 % CABG
68
67
67
36
67
66
68
52
68
% valve
14
16
19
37
19
11
18
14
18
 % CABG/valve
17
15
14
27
14
12
14
34
14
% internal thoracic artery usage
73
77
82
58
79
80
79
49
80
% median pump time (>120 min)
34
28
28
41
30
27
39
 68
21
% median crossclamp time (>90 min)
30
26
24
37
25
23
25
47
24

Median age: 67 years with a lower quartile of 59 years and and upper quartile of 74 years

Median BMI: 26.6 with a lower quartile of 23.9 and an upper quartile of 29.7

Median serum albumin: 3.5 g/dL with a lower quartile of 2.7 g/kL and an upper quartile of 4.1 g/dL 

Attrition - None

Ethnicity - Not specified

Comparisons of study group:

  • Patients witha serium albumin level of less than 2.5 g/dL and a BMI <20 had a greater number of comorbidities and risk factors
  • In patients who  underwent CABG or CABG/valve procedures, there was no difference in internal thoracic artery usage between patients with a BMI of 20-30 and those with a BMI >30.
  • Women constituted the largest percentage of patients witha BMI < 20

Location: Brigham and Women's Hospital in Boston, MA

 

Summary of Results:
  • Both BMI < 20 and preoperative hypoalbuminemia independently predicted increased mortality and postoperative complications.
  • Obesity did not predict increased mortality after cardiovascular surgery, however there was an increased risk of atrial arrhythmias, deep sternal wound infection, and saphenous vein harvest site infections
  • Obesity was associated with reduction in risk of re-exploration for bleeding.
  • Preoperative malnutrition associated with poor outcoje after cardiac surgery
  • Serum albumin < 2.5 mg/dL associated with increased length of stay and mortality

Outcomes by Albumin Level after Multivariate Analysis  

Outcome
Albumin < 2.5
Albumin 2.5 – 3.5
 
OR (95% CI)
P value
OR (95% CI)
P value
Death
2.0 (1.3-3.0)
.002
1.1 (0.8-1.6)
.6
Renal failure
2.0 (1.3-3.2)
.002
1.9 (1.3-2.7)
.001
Low cardiac output
1.6 (1.2-2.1)
.001
1.2 (1.0-1.5)
.1
New atrial fibrillation
1.4 (1.2-1.7)
.0001
1.3 (1.2-1.5)
.0001
Re-exploration for bleeding
1.4 (1.0-2.1)
.04
0.8 (0.6-1.1)
.3
ICU > 3 days
1.7 (1.4-2.1)
.0001
1.3 (1.1-1.6)
.006
Ventilatory support >1 day
2.5 (2.0-3.1)
.0001
1.5 (1.2-1.7)
.0001
Length of stay > 10 d
1.9 (1.5-2.4)
.0001
1.6 (1.3-1.8)
.0001
P value > .05 for CVA/TIA, pneumonia, sepsis, MI, deep sternal wound infection, leg infection.

Outcomes by BMI after Multivariate Analysis

Outcome
BMI < 20
BMI > 30
 
OR (95% CI)
P value
OR (95% CI)
P value
Death
2.0 (1.2-3.6)
.009
1.4 (0.9-2.1)
.1
CVA/TIA
1.7 (1.0-2.9)
.03
0.9 (0.6-1.4)
.7
Renal failure
2.0 (1.2-3.5)
.01
1.1 (0.7-1.6)
.7
Pneumonia
2.2 (1.3-3.8)
.003
1.4 (0.9-2.0)
.1
New atrial fibrillation
1.0 (0.7-1.3)
.9
1.2 (1.0-1.4)
.02
Re-exploration for bleeding
2.1 (1.3-3.3)
.001
0.6 (0.4-4.8)
.005
Deep sternal wound infection
0.4 (0.1-3.0)
.4
2.4 (1.5-3.8)
.0001
Leg infection
2.0 (0.9-4.7)
.1
2.1 (1.4-3.1)
.0001
P value > .05 for sepsis, MI, low cardiac output, ICU > 3 days, ventilatory support >1 day, length of stay > 10 days

Author Conclusion:

Hypoalbuminemia and low BMI each independently predict increased morbidity and mortality after cardiac operations.

Funding Source:
University/Hospital: University Maastricht (Netherland)
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? 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? Yes
  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%.) N/A
  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
  4.5. 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? 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
  5.4. 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? 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? 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)? 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
  8.7. 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