Endocrine Abstracts

History: A 54 years old gentleman was admitted to the hospital after being found unconscious at home by his wife with a tongue bite and urinary incontinence. He had perineal approach biopsy 2 days ago for prostate cancer. Since biopsy, he had poor urine output with clots and dribbling. He also gave 2 days history of constipation. Wife was a doctor and mentioned that she palpated a distended bladder the night before. On examination, he was haemodynamically stable although he did have a palpable and tender bladder. He was confused and lethargic but no focal neurological deficit.

Investigations and treatment: His sodium on admission was 100 mmol/l on arterial blood gas and 109 mmol/l on the lab result. Serum osmolality at that point was 233 mOsmol/kg. He was given 250 ml of 1.8% hypertonic saline over 20 min but sodium remained 100 mmol/l on repeat blood gas and 109 mmol/l on the lab report. He was catheterized and drained 1.5 l of urine. His sodium came up to 113 mmol/l over the next 5 h. He was then given maintenance 0.9% normal saline 50 ml/h. His sodium steadily increased to 122 mmol/l over 10 h and then to 126 mmol/l in 21 h.

Results: Admission bloods showed urea 6.8 mmol/l, creatinine 158 μmol/l, eGFR 40. Repeat bloods post catheterization at 2 h improved to urea 5.6 mmol/l, creatinine 106 μmol/l, eGFR 63 in keeping with resolved obstructive uropathy. Paired serum and urine osmolalities and urine sodium were not sent until 10 h after admission. Patient had already received treatment with hypertonic saline and drained 1500 ml of urine. Results showed serum osmolality 253 mOsmol/kg, urine osmolality 229 mOsmol/kg, urinary sodium <10 mmol/l, normal cortisol and thyroid function tests. CT head was also reported normal.

Conclusion and points for discussion: Urinary retention is one of the unrecognized causes of hyponatremia. The mechanism is mainly due to stretching the bladder wall causing activation of sympathetic nervous system and inappropriate release of ADH hormone. In our case, the patient initially did not respond to hypertonic saline but sodium went up quickly after bladder catheterization. Fortunately, rapid sodium rise did not cause him any complications. Treating physicians should be aware of this association and the quick sodium rise following catheterization and be ready to do interventions as appropriate.