Obstructive Nephropathy

Obstructive nephropathy is renal parenchymal damage caused by impaired urine flow, with raised intratubular pressure, hydronephrosis, tubular atrophy and interstitial fibrosis.

• Causes by site: urethra (posterior urethral valves, stricture, phimosis), bladder outlet (benign prostatic hyperplasia, prostate cancer, bladder tumour, neurogenic bladder, stones), ureter (stones, strictures, schistosomiasis, tuberculosis, retroperitoneal fibrosis, malignancy, pelvic masses, iatrogenic ligation), and pelviureteric junction obstruction.
• In Kenya, cervical cancer, schistosomiasis, prostate disease and stones are the common causes.
• Reversibility depends on duration and completeness: recovery is likely within 4 to 6 weeks of complete obstruction, partial recovery up to 12 weeks, and little after longer.

Acute: loin pain, anuria or oliguria alternating with polyuria, suprapubic pain and a palpable bladder.

• Chronic: lower urinary tract symptoms (hesitancy, poor stream, nocturia, dribbling, retention), recurrent infection, polyuria, hypertension, fatigue, and a palpable kidney.
• Chronic obstruction may be silent until renal failure; tubular defects produce polyuria and nephrogenic diabetes insipidus, hyperkalaemic type 4 renal tubular acidosis and sodium wasting.
• Differential diagnosis: prerenal or intrinsic acute kidney injury, chronic kidney disease of other cause, diabetes insipidus, polycystic kidneys, renal tumour.
• Complications: acute and chronic kidney disease, hypertension, hyperkalaemia, metabolic acidosis, infection and pyonephrosis, post-obstructive diuresis with dehydration, stones, and end stage kidney disease.

Bladder scan or ultrasound for post-void residual (above 100 mL is abnormal), renal ultrasound for hydronephrosis (dilated calyces, thinned cortex), though early obstruction, dehydration, retroperitoneal fibrosis and encasement may show no dilatation.

• Creatinine, urea, electrolytes (potassium, bicarbonate), full blood count, urinalysis and culture, PSA with prostate examination in men.
• Non-contrast CT to find the cause (stone, mass, fibrosis); contrast CT or MR urography; diuretic renography to assess function and obstruction; cystoscopy and urethrography for lower tract disease.
• Pelvic examination and imaging for cervical or gynaecological malignancy in women.

Supportive: monitor fluid balance, urea, creatinine and potassium; treat hyperkalaemia (calcium gluconate 10 percent 10 mL IV over 5 to 10 minutes, insulin 10 units with 25 g glucose IV, salbutamol 10 to 20 mg nebulised, sodium polystyrene or sodium zirconium cyclosilicate 10 g three times daily); sodium bicarbonate 1.26 percent for acidosis.

Pharmacological

• Infection: ceftriaxone 2 g IV daily, gentamicin 5 mg/kg daily (adjust for renal function), or piperacillin-tazobactam 4.5 g IV every 8 hours; continue after drainage for 7 to 14 days.
• Benign prostatic hyperplasia: tamsulosin 0.4 mg daily and finasteride 5 mg daily.
• Retroperitoneal fibrosis: prednisolone 40 to 60 mg daily tapered over 6 to 12 months, with ureteric stents.
• Tuberculous strictures: full anti-tuberculosis therapy (rifampicin, isoniazid, pyrazinamide, ethambutol for 2 months then rifampicin and isoniazid for 4 months) with prednisolone 20 to 40 mg for stricture prevention.
• Schistosomiasis: praziquantel 40 mg/kg single dose.

Procedures

• Relieve obstruction promptly: urethral catheter 14 to 16 Fr (suprapubic catheter if urethral access fails) for lower tract obstruction; ureteric stent or percutaneous nephrostomy for upper tract obstruction.
• Post-obstructive diuresis (urine above 200 mL/h for 2 hours, or above 3 L daily): replace with 0.45 percent sodium chloride at 50 to 75 percent of the previous hour's urine output; monitor weight, urea and electrolytes.
• Definitive: transurethral resection of the prostate, urethrotomy, stone removal, pyeloplasty for pelviureteric junction obstruction, ureteric reimplantation, oncology for malignancy.

Special groups: children (early valve ablation), pregnancy (stent, nephrostomy), men with high pressure chronic retention (catheter, gradual decompression is not required).

Red flags: anuria, potassium above 6.5 mmol/L, sepsis, solitary kidney, bilateral hydronephrosis, uraemic symptoms.

Follow-up: creatinine and ultrasound at 1 to 2 weeks and 6 to 12 weeks; dialysis if renal function does not recover; yearly renal review for chronic disease.