Evaluation of a variable ratio cardioplegia system.

Gish Biomedical has designed a blood cardioplegia delivery system (MyoManager) which is purported to provide rapid control of blood and crystalloid solution ratios for myocardial preservation. The present study was designed to evaluate the ability of this device to provide cardioplegia solutions of specific hematocrit and potassium ion concentrations ([K+]). An in vitro circuit was designed whereby a blood perfusate with a [K+] of 5 mEq/L was mixed with a base crystalloid solution containing 210 mEq/L of K+. Data was collected at several blood to crystalloid ratios (1:1, 4:1, 8:1, 16:1, 25:1), and at four delivery rates (100, 150, 200, 250 ml/min). Predicted and observed values of total cardioplegia volume, hematocrit, crystalloid volume, and [K+] were statistically (ANOVA) analyzed, and statistical significance accepted at p 0.05. There were no statistically significant differences observed at any flows or ratios in hematocrit. However, at 100 ml/min flow rates, the crystalloid delivery volume difference of 2.4 +/- 2.0 ml was significantly higher than that observed at 250 ml/min, 1.5 +/- 1.5 ml (p < 0.02) and at 200 ml/min flow rates, 1.5 +/- 1.6 ml (p < 0.02). There was no statistical significance in [K+] difference between flows across all ratios. However, within ratios, a significant difference in [K+] at 100 ml/min, 1:1 blood to crystalloid ratio, was observed (p < 0.0001) versus all other ratios and flows. The only statistically significant difference that was shown in total cardioplegia delivery volume was observed between 100 and 200 ml/min (p < 0.04) when analyzed across all ratios. The data suggests that the MyoManager effectively provides precise control of [K+] and hematocrit at cardioplegia flows greater than 100 ml/min.