EAL

CI: Blood Glucose Control (2009)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To determine if perioperative glycemic control (> 36 hours post op while hospitalized) influences development of infection after coronary artery bypass graft (CABG) surgery.

Inclusion Criteria:

Patients with diabetes who underwent CABG surgery at Johns Hopkins Hospital from 1/1/1990 through 12/31/1995) as identified through a surgical log.

Exclusion Criteria:

Patients excluded if:

medical record had fewer than 3 capillary blood glucose (CBG) readings on each postoperative day
infectious complications within 36 h of surgery
evidence of preoperative infection (positive culture, infiltrate, use of antibx on admission)
death within 36 h of surgery

Description of Study Protocol:

Recruitment Medical record review

Design Cross-Sectional Correlation Study

Blinding used (if applicable)

Those reviewing medical records collected CBG data before collecting data on infection in effort to strengthen validity.

Intervention (if applicable)

None

Statistical Analysis

Prospective analysis with independent variable was perioperative glucose concentration (mean of 6 measures through end of POD 1) and dependent variable of subsequent infectious complication:

Univariate analysis reported by quartiles with 95% Confidence Intervals (CIs) around incidence rates.
Multiple logistic regression models to determine relative odds and 95% CIs of infection by glucose quartile after adjustment for demographic and clinical characteristics that might act as confounders.
Subsidiary analysis in which infectious complications occurring on POD 2 were censored to create a 24-h lag between assessment of exposure and outcome.

Retrospective analysis where independent variable was case-control status (infectious complication vs. none) and dependent variable was mean postop glucose concentration (cumulative up to 11:59 PM on day before case-control status was accessed):

tested individuals who developed infection on POD 2 or later were compared with individuals who had no infectious complication and were alive and in hospital on POD 3 (included 25 patients who were excluded from prospective analysis due to infection on POD 1)
t-testing using

Data Collection Summary:

Timing of Measurements

CBG values had to have be measured at least 4 h apart and recorded in chart

Dependent Variables

Pneumonia (defined by positive sputum culture or new infiltrate on chest Xray)
Urinary tract infection (defined by positive urine culture or pyuria)
Wound infection (defined by positive wound culture, dehiscence, drainage, or cellulitis
other infection (defined by other positive culture or addition of new antibiotics prompted by fever)

Independent Variables

Perioperative glycemic control (measured by CBG finger sticks)

Control Variables

CBG was not measured for 36 h after surgery. Authors discussed this 36 h lag as included b/c they wanted to characterize glycemic control optimally.

**See statistical section for more discussion about how investigators manipulated variables for prospective vs. retrospective analysis.

Description of Actual Data Sample:

Initial N: (e.g., 731 (298 males, 433 females))

Attrition (final N): n/a as this was a medical record review with no treatment

Age: mean age 63

Ethnicity: 81% caucasian

Other relevant demographics:

Anthropometrics - when separated into quartiles by glucose control, groups appeared to have similar baseline characteristics including age, gender, race, Charlson Comorbidity Index, APACHE III index. SICU stay and urine protein may have differed, but no mean separation analysis was described.

Location: Johns Hopkins Hospital

Summary of Results:

Model 1 Unadjusted model-- correlated perioperative glycemic control mean CBG > 200 mg/DL with odds of infection: Not Significant (P=0.21)

Model 2 Adjusted to account for effects of age, sex, race, comorbidity, SICU stay--correlated perioperative glycemic control mean CBG > 200 mg/DL with odds of infection: Significant with (P=0.05)

Model 3 Adjusted for age, sex, race, comorbidity, SICU stay, proteinuria and includes 24-h lag between exposure and outcome assessment; limited to the 375 individuals with data available on proteinuria: Not Significant with (P=0.19)

Other Findings

Author Conclusion:

In patients with DM who undergo CABG, postoperative hyperglycemia is an independent predictor of short-term infectious ocmplications. Glucose concentration target should be < 200 mg/dl to reduce risk of infection.

Funding Source:

Reviewer Comments:

The authors list five possible limitations of the study in the conclusions section. Unfortunately, the lack of adequate design in this study may limit its usefulness.

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)	???
	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?	???
	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)	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.)	No
	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?	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?	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?		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?	N/A
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	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?	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
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	N/A
7.	Were outcomes clearly defined and the measurements valid and reliable?		???
	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?	N/A
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	???
	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?	No
	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)?	Yes
	8.6.	Was clinical significance as well as statistical significance reported?	No
	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