Search
postrenal azotemia; obstructive uropathy
Also see acute renal failure.
Etiology:
1) ureteral obstruction
a) clot
b) calculus
c) sloughed papillae (papillary necrosis)
d) external compression
1] tumor (colon cancer)
2] retroperitoneal fibrosis
3] fecal impaction, especially in the elderly
e) abdominal compartment syndrome
2) bladder outlet obstruction (98% of males)
a) neurogenic bladder
b) prostatic hypertrophy [3]
c) carcinoma
1] prostate cancer
2] cervical cancer
3] bladder cancer
d) urinary calculus
e) thrombus (blood clot)
f) urethral stricture
g) phimosis
h) fecal impaction, especially in the elderly
i) abdominal compartment syndrome
3) bilateral renal vein occlusion (thrombosis)
4) surgery
a) abdominal
b) pelvic
c) gynecologic
5) radiation therapy
Pathology:
1) increased ureteral pressure proximal to site of obstruction may lead to irreversible renal damage
2) obstruction must involve outflow tract of both kidneys (single kidney if other kidney is non functional) for azotemia
3) tubular injury associated with urine concentrating defect may occur
4) osmotic diuresis due to excretion of retained solute follows relief of urinary tract obstruction
Clinical manifestations:
1) flank pain
2) abdominal pain
3) nausea/vomiting
4) anuria suggest complete obstruction
5) oliguria, polyuria, or nocturia may accompany partial obstruction
Laboratory:
1) BUN/creatinine may be elevated secondary to increased tubular urea resorption
2) check serum K+ for hyperkalemia with severe azotemia
3) urinary indices & urinary Na+ are variable
4) urine sediment is generally without significant cellular elements
5) proteinuria is generally absent
6) evaluation of serum & urine electrolytes with post-obstructive diuresis
Radiology:
1) renal ultrasound to delineate hydronephrosis*
- include bladder ultrasound to assess post-void residual volume
2) computed tomography (CT) may be helpful
a) when results of ultrasound are equivocal
b) retroperitoneal fibrosis
c) periureteral metastatic disease
3) avoid radiographic contrast (CT urography) with acute renal failure [5]
4) anterograde or retrograde pyelography rarely used
* imaging modality of choice [1]
* renal ultrasound not necessary for urinary retention due to benign prostatic hypertrophy (BPH) [4]
Management:
1) relieve obstruction, monitor input & output - foley catheter
2) fluid restriction if euvolemic or volume overloaded
- 1 to 1.5 L/day
3) postobstructive diuresis may occur after relief of obstruction
4) prognosis is good if obstruction is relieved within 1-2 weeks of onset, but tubular defects may persist
5) little recovery may be expected if high-grade obstruction exceeds 3 months
6) also see urinary retention
Related
acute renal failure (ARF)
Specific
abdominal compartment syndrome
urethral stricture
urinary retention
General
azotemia
urologic disease
References
- Medical Knowledge Self Assessment Program (MKSAP) 11, 15, 16,
17, 18, 19. American College of Physicians, Philadelphia 1998, 2009,
2012, 2015, 2018, 2021.
- Harrison's Principles of Internal Medicine, 13th ed.
Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 1266
- Prescriber's Letter 11(1):3 2004
Detail-Document#: 200105
(subscription needed) http://www.prescribersletter.com
- NEJM Knowledge+ Question of the Week. July 17, 2018
https://knowledgeplus.nejm.org/question-of-week/1216
- NEJM Knowledge+ Nephrology/Urology