Observations on the Hyponatremia following Mitral Valvulotomy

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Abstract
Thirty-seven patients subjected to mitral valvulotomy were studied before and after operation with regard to the incidence, extent, and mechanism of postoperative hyponatremia. Balances of water, sodium, and chloride were carried out on 27 patients. The serum sodium fell below 131 mEq. per liter in 16 cases in the immediate postoperative period, the serum chloride fell below 99 mEq. per liter in all cases but one and below 90 mEq. per liter in 11 cases. The small negative balances of sodium and chloride were inadequate, by themselves, to account for the observed hyponatremia in any case. Appreciable (over 100 mEq.) intracellular shifts of sodium (using the chloride space as a reference) were associated with hyponatremia in only three cases. The retention of water during the immediate postoperative period (allowing for insensible losses) was enough to explain the observed hyponatremia in all but three cases, although the level of fluid intake was not well correlated with the occurrence of hyponatremia. These results indicate the presence of an unusually prolonged antidiuretic stimulus in these patients, the etiology of which remains uncertain. Except in a few cases it is unnecessary to correct the hyponatremia with hypertonic salt, since it is usually a transient, limited, and essentially asymptomatic phenomenon.