Acute Urinary Retention with Severe Bladder Distension and Overcorrection of Hyponatremia During Postobstructive Diuresis

Introduction: Acute urinary retention with obstructive renal failure is followed by a post obstructive diuresis upon relief of bladder outlet obstruction (BOO). A tubular dysfunction associated with post-obstructive diuresis is an ADH resistant concentrating defect. Without adequate fluid replacement this can lead to polyuria and hypernatremia. We report a case where relief of BOO led to over-correction of severe hyponatremia. Case Description: A 74-year-old man came to the ED with 4 days of difficult urination, abdominal distension, and constipation, after 7 days of Bactrim for possible UTI. He had suprapubic fullness and lower abdominal tenderness. Labs: Na 117, K 5.8, Cl 81, HCO3 24 (all mmol/L), BUN 85 mg/dL, Creatinine 5.60 mg/dL (Baseline 1.0), urine Osm 269 mOsm/kg, and serum Osm 271 mOsm/kg. CT A/P: Massively distended bladder (28 cm) with bilateral hydronephrosis and hydroureters (Figure). 7 L of urine was drained via initial foley placement then 200 ml/hr. Serum Na increased from 117 to 130 mmol/L over 9 hours for which a D5W drip was started at 150 ml/hr for 16 hours and two doses of 2 mcg DDAVP was given which decreased Na to 123 over the next 23 hours. D5W was then stopped, and sodium was improved to 133 mmol/L over 48 hours. BUN fell to 19, and an ultrasound showed bladder decompression and resolution of bilateral hydronephrosis. Discussion: First, this case highlights an unusually large bladder of 28 cm with acute obstructive renal failure; such large bladder distention is rarely seen with acute urinary tract obstruction. The case also highlights the overcorrection of hyponatremia during the post obstructive diuresis due to the associated concentrating defect causing water loss and thus rapid correction of the hyponatremia.