Preoperative hyponatremia and cardiopulmonary bypass: yet another factor for cerebral dysfunction?

Hyponatremia is common in patients prior to cardiopulmonary bypass (CPB), usually secondary to diuretic therapy. Rapid correction of chronic hyponatremia, which potentially occurs on commencing CPB, may in susceptible patients result in central pontine myelomatosis. There are three parts to this study. Part 1: Patients (n = 170) undergoing CPB with preoperative hyponatremia were analyzed by degree of hyponatremia, additive EuroSCORE, length of stay - intensive care and total hospital, and mortality. Part 2: Sodium concentrations of different prime constituents used clinically were collated from the literature. Part 3: Mathematical modeling of the effects of patient size, sex, preoperative hemoglobin, prime solution, and prime volume with regard to the effect on serum sodium during cardiopulmonary bypass was analyzed, assuming a preoperative serum sodium of 125 mmol/L. Part 1: Patients with preoperative hyponatremia, even after matching by additive EuroSCORE, have longer length of stay - intensive care and total hospital, but not significantly different mortality rates. Part 2: Sodium concentrations of different primes used clinically varied from 0 mmol/L to 160 mmol/L. Part 3: Mathematical modeling revealed that patient size, sex, preoperative hemoglobin, prime solution, and prime volume all can exert a significant effect on serum sodium on initiation of cardiopulmonary bypass. Further work is needed to evaluate the roles of sudden changes in serum sodium, with regard to a rapid correction of chronic hyponatremia, or the rapid creation of acute hyponatremia, and cerebral outcomes in patients undergoing CPB.