The authors concluded that miniaturised cardiopulmonary bypass (mini-CPB) may be associated with lower risk of post operative stroke, blood loss and mortality in comparison with conventional cardiopulmonary bypass (C-CPB) conventional cardiopulmonary bypass. The reporting of methodology in the review was weak and the results were based on small heterogeneous studies. The authors' conclusion should be treated with caution.

To compare miniaturised cardiopulmonary bypass to conventional cardiopulmonary bypass and establish which is most clinically effective.

PubMed and The Cochrane Library were searched to June 2008. Search terms were reported. Electronic searches of related articles were performed. Handsearches of bibliographies and related journals were performed.

Randomised prospective studies that compared miniaturised cardiopulmonary bypass (mini-CPB) to conventional cardiopulmonary bypass (C-CPB) in adult patients who underwent isolated coronary artery bypass surgery, heart-valve surgery or combined surgical procedures were eligible for inclusion. Included studies needed to report at least two of the following clinical outcomes: death, stroke, intensive care unit length of stay, in-hospital length of stay and blood loss and/or reoperation for bleeding. Studies that evaluated mini-CPB with any heart beating procedure were excluded.

Average age of participants ranged from 59.6 to 71 years old. Included procedures were either isolated aortic valve replacements or isolated coronary artery bypass grafting. Where reported, target activated clotting times ranged from 250 to 480 seconds. A variety of cardiopulmonary bypass systems was used for both mini-CPB and C-CPB. CPB duration ranged from 61.2 to 147 minutes. Where reported, aortic cross-clamping time ranged from 31.4 to 107 minutes and left ventricular ejection fraction ranged from 46% to 63.1%.

The authors did not state how many reviewers selected the studies.

The authors did not state that they assessed validity.

Continuous outcome endpoints were extracted to calculate weighted mean differences (WMD) and 95% confidence intervals (CI). Dichotomous outcome endpoints were extracted to calculate odds ratios (OR) and 95% CI.

The authors did not state how many reviewers extracted data.

Pooled weighted mean differences (with 95% CI) were calculated for continuous data. Pooled odds ratios (with 95% CI) were calculated for dichotomous data. Heterogeneity was assessed using the I² test; a p value less than 0.05 indicated statistically significant heterogeneity. A random-effects meta-analysis was used to synthesise heterogeneous data. A fixed-effect model was used to synthesis homogenous data. Subgroup analysis investigated results for isolated coronary bypass grafting.

Thirteen prospective randomised trials (n=1,161) were included in the meta-analysis.

Comparison of mini-CPB (n= 562) and C-CPB (n=599) clinical data found that patients in the mini-CPB group were statistically significantly older than those in the C-CPB group. No significant differences were found between the two groups for lower ventricular ejection fraction, duration of bypass procedure and aortic cross-clamping time.

Comparison of mini-CPB and C-CPB found no significant differences in rates of in-hospital mortality (13 studies), length of stay in the intensive care unit (11 studies) or resternotomy (four studies). There was a significant decrease in risk of postoperative stroke for mini-CPB compared to C-CPB (OR 0.25, 95% CI 0.06 to 1.00; 12 studies, n=1,061) and for postoperative blood loss (WMD -96.55, 95% CI -147.48 to -45.62; 10 studies, n=1,061). Analysis of postoperative blood loss and length of stay in the intensive care unit showed significant heterogeneity (I²=85%).

Subanalysis of isolated coronary artery bypass surgery procedures (n=1,021) found no significantly different results to the overall procedures.

Use of mini-CPB may be associated with lower risk of postoperative stroke, blood loss and mortality. Larger and more homogenous studies were required to obtain more conclusive results.

The review addressed a clear research question with clear inclusion criteria. The searches were not explicitly described, but the authors indicated that two databases were searched. Unpublished studies were not sought systematically and as publication bias was not assessed it was unclear whether this had an impact on the review. The likelihood of language bias could not be assessed as the review did not state whether language restrictions were applied. Validity was not formally assessed. No steps to minimise errors and bias were reported throughout the review process. Details on included studies were reported and for most analyses the chosen method of synthesis appeared appropriate. However, some combined very heterogeneous studies and the rationale for these should be questioned. The results of the review were based on small studies, some of which contained few events. In view of the weak reporting of methodology and the paucity of studies, the authors conclusions should be treated with caution.

Practice: The authors did not state any implications for practice.

Research: The authors stated that larger trials were required that involved high-risk patients and/or more complex cardiac procedures along with more homogenous methods to provide more conclusive results.

None stated.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.