Proportioned blood cardioplegia delivery systems- are you del iveri ng the [K+] you expect?

Abstract

This study was conducted to compare the actual potassium concentration [K+] delivered from a standard 4:1 ratio blood cardioplegia solution with the predicted [K+]. We found that the delivered [K+] ranged from 18.15 to 21.2 mEq/I although we predicted 22.0 mEq/I from our mathematical model. The factors that contributed to this difference were investigated. The ratio of blood:crystalloid was determined by: (1) potassium dilution technique; (2) volume output technique; and (3) from the manufacturer's tubing specifications and tolerances. This resulted in blood:crystalloid ratios of 3.86:1 (3.35-4.49:1), 3.74:1, and 4.0:1 (3.47-4.68:1), respectively. Analysis of the crystalloid component revealed an average [K+] of 75.7 mEq/I (70.0-81.5 mEq/I). Patient [K+] during the study ranged from 4.3 to 6.4 mEq/l. When the effect of clinical extremes in ratio, crystalloid [K+], and patient [K+] were considered, a range of cardioplegia [K+] of 16.0-24.3 mEq/I would be predicted. It was concluded that the ability to control the delivered [K+] with any precision is limited. Manufacturers should (1) match the tubing in such a way as to minimize ratio extremes and (2) adopt a tubing tolerance of ± 0.003 inches. Perfusionists should (1) analyse the crystalloid solution prior to cardiopulmonary bypass (CPB) and (2) analyse the cardioplegia [K+] when there is difficulty arresting the heart or if the patient [K+] is excessively elevated.