Physiopathology of hypernatremia following relief of urinary tract obstruction.

We report a case of postobstructive hypernatremia, and illustrate its pathogenesis and treatment. Physicians should be aware of this condition, given its high mortality rate (up to 70%), the high prevalence of potentially obstructive prostatic disease in elderly people and the peculiar sensitivity of this age group to disorders of osmotic regulation. Knowledge of the processes involved in osmoregulation has provided insights into the pathogenesis of this condition, which includes at least three factors: (i) decreased efficacy of the thirst mechanism in elderly patients, (ii) water loss in excess of effective solutes, resulting from osmotic diuresis from urea and transient renal tubular unresponsiveness to antidiuretic hormone, and (iii) inadequate fluid administration and failure to induce a positive fluid balance. These insights led to the development of specific strategies aimed at adequate correction of hypernatremia. Initial therapy should be rapid infusion of normal saline (or half-normal saline) coupled to administration of free water to restore euvolemia and correct hypernatremia, relying on repeated calculations of the free water deficit and taking into account ongoing urinary and insensible losses.