Continuous warm blood cardioplegia is considered to be an effective method for myocardial protection. However, frequently the flow of the cardioplegia needs to be interrupted for better visualization. Intermittent warm blood cardioplegia was reported to be safe by some investigators. To assess the degree of this safety, 76 patients who underwent operations for coronary or valvular disease, or both, were divided into two groups of 38 patients each. The two groups were well matched for age, ejection fraction, number of coronary bypasses and type of valvular procedures. Cold blood cardioplegia (CBC) was used intermittently every 15 min in the first group while the second group received warm blood cardioplegia (WBC) intermittently every 15 min. The clamp time range was 50-140 min. There were no deaths in either group, four myocardial infarctions occurred, two in each group. Low cardiac output occurred in 13 patients of the WBC group and in 7 patients of the CBC group, electrocardiogram (ECG) global ischemic changes were recorded in 14 patients of the WBC group compared to 6 patients of the CBC group. Statistically the results indicate that the techniques are comparable if the clamp time is less than 90 min. However, after 90 min the development of ECG changes and low cardiac output are significantly higher when WBC is used P < 0.001. Therefore, it is concluded that using the WBC intermittently is as safe as CBC when the clamp time is less than 90 min, however extra precautions are needed with longer clamp times.
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Ali et al. (1994) studied this question.