The role of the priming fluid in the metabolic response to cardiopulmonary bypass in children of less than 15 kg body weight undergoing open-heart surgery.

The major metabolic response to open-heart surgery using cardiopulmonary bypass has been shown in adults to be modified by the components of the pump priming fluid. This effect is likely to be more significant in children. Data on 29 children less than 15 kg body weight are presented. Patients were randomised to receive a prime containing one of three crystalloid priming fluids: 100% Hartmann's (H), 50% Hartmann's + 50% 5%-Dextrose (HD), or 100% Plasmalyte 148 (P). The remainder of the prime was CPD stored blood and the prime was buffered with sodium bicarbonate. Severe hyperglycaemia 22.4 +/- 1.3 mmol/l occurred during bypass in the HD group but moderate hyperglycaemia occurred in the other prime groups. Hyperlactataemia occurred in all prime groups during bypass and was highest in the H prime group at 3.9 +/- 0.4 mmol/l. These changes in intermediary metabolites were only partly explained by the crystalloid components of the priming fluid. A subsiduary study revealed the important contribution of CPD stored blood to those intermediary metabolite concentrations. Therefore, the well recognised changes in intermediary metabolites as components of the metabolic response to surgery, namely hyperglycaemia and hyperlactataemia were augmented by the composition of the priming fluids. In addition, CPD stored blood and the sodium bicarbonate buffer increased the sodium concentration of the prime to hypernatraemic levels in both the H and P groups which caused an increase in sodium concentration during bypass. Therefore important changes during bypass occur as a direct result of the individual components of the priming fluid. These changes may result in osmolal flux, hyperglycaemia and hyperlactataemia, all of which have been reported to be potentially harmful.