Severe hyponatremia without severe hypoosmolality following transurethral resection of the prostate (TURP) in end-stage renal disease.

A 55-year-old man on chronic hemodialysis underwent a transurethral resection of the prostate (TURP), during which 3% sorbitol solution was used for urethral irrigation. Following the procedure, he developed symptomatic hyponatremia (serum sodium, 106 mEq/L), but had only mild hypoosmolality (serum osmolality, 269 mosm/kg). The "osmolal gap" was 47 mosm/kg, probably from sorbitol absorbed systemically during the TURP. Hemodialysis raised the serum sodium to 118 mEq/L, and the serum osmolality to 284 mosm/kg, while lowering the osmolal gap to 26 mosm/kg. The presence of severe hyponatremia with only modest hypoosmolality may occur in patients with renal failure following the systemic absorption of hypotonic fluids containing solutes such as sorbitol and mannitol. Hemodialysis offers the advantages of correcting the hyponatremia while removing the unmeasured solute, thus preventing rapid increases in the serum osmolality.