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A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether blood cardioplegia is clinically superior to crystalloid cardioplegia for myocardial protection. Altogether 501 papers were identified. We selected 22 papers that represented the best evidence to answer the question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. This is a difficult topic to review, as the techniques studied in the many trials performed vary widely. Factors which may vary include warm or cold blood cardioplegia, antegrade and retrograde administration, systemic hypothermia or normothermia, topical heart cooling, high and low potassium solutions, 'hot shots', warm induction, volume of cardioplegia, patient factors and bypass times. However, three papers stand out. The meta-analysis of 34 randomised trials by Prof Fremes (2006) found a significantly lower incidence of low output syndrome (LOS) and CK-MB release with blood cardioplegia. He found no differences in myocardial infarction or mortality. This meta-analysis was confounded, however, by the fact that he was unable to extract data on LOS and CK-MB from the two largest trials which contributed over half the patients in his paper and are significantly larger than all other studies. The first paper by Ovrum (2006) randomised 1440 patients to antegrade cold blood or crystalloid and found no clinical differences, and the second paper by Martin (1994) of 1001 patients compared warm blood to cold crystalloid but the study had to be stopped due to a high incidence of neurological events in the warm blood group. We reviewed a further 18 randomised trials reporting over 50 patients. Of these, 10 reported some statistically significant clinical outcomes in favour of blood cardioplegia and five reported statistically significant differences in enzyme release in favour of blood cardioplegia. A recent survey of UK practice found that 56% of surgeons use cold blood cardioplegia, 14% use warm blood cardioplegia, 14% use crystalloid cardioplegia, 21% use retrograde infusion and 16% do not use any cardioplegia. The papers presented in our review support most of these practices!

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