Plasma hypoxanthine levels during crystalloid and blood cardioplegias: warm blood cardioplegia increases hypoxanthine levels with a greater risk of oxidative stress

BACKGROUND: Patients undergoing cardiopulmonary bypass (CPB) are subjected to severe oxidative stress, and frequently show evidence of acute lung injury post surgery. Associations between acute lung injury, oxidative stress, and aberrant ATP catabolism have been made and prompted us to consider whether the purine metabolites xanthine and hypoxanthine alter significantly during CPB when different types of cardioplegia are used. METHODS: Experimental design: retrospective follow up study on stored plasma samples from patients randomly selected to receive either warm blood, cold blood, or crystalloid cardioplegia. Setting: adult intensive care unit of post graduate teaching hospital. Patients: thirty-eight patients undergoing aortic valve replacement, with or without artery grafting. Operation was carried out by a single surgeon. Interventions: all patients received either a homograft aortic valve or a stentless porcine valve. RESULTS: No significant differences in xanthine levels at any time points during CPB, or between the different cardioplegic groups. Hypoxanthine levels were, however, significantly higher in patients receiving warm blood cardioplegia (74.84+/-16.715 microM, p=0.0151), and was most marked at time point 3 when the aortic cross clamp was released. Patients receiving crystalloid cardioplegia showed higher levels of hypoxanthine (44.56+/-10.16 microM) than those receiving cold blood cardioplegia (21.57+/-7.106 microM). CONCLUSIONS: Considering these data together, it suggests that aberrant ATP catabolism, characteristic of ischaemia/reperfusion, is further disturbed during warm blood cardioplegia leading to a marked increase in plasma hypoxanthine levels. This has the potential to further increase oxidative stress during CPB.