postrenal azotemia; obstructive uropathy
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Introduction
Also see acute renal failure.
Etiology
- ureteral obstruction
- clot
- calculus
- sloughed papillae (papillary necrosis)
- external compression
- tumor (colon cancer)
- retroperitoneal fibrosis
- fecal impaction, especially in the elderly
- abdominal compartment syndrome
- bladder outlet obstruction (98% of males)
- bilateral renal vein occlusion (thrombosis)
- surgery
- abdominal
- pelvic
- gynecologic
- radiation therapy
Pathology
- increased ureteral pressure proximal to site of obstruction may lead to irreversible renal damage
- obstruction must involve outflow tract of both kidneys (single kidney if other kidney is non functional) for azotemia
- tubular injury associated with urine concentrating defect may occur
- osmotic diuresis due to excretion of retained solute follows relief of urinary tract obstruction
Clinical manifestations
- flank pain
- abdominal pain
- nausea/vomiting
- anuria suggest complete obstruction
- oliguria, polyuria, or nocturia may accompany partial obstruction
Laboratory
- BUN/creatinine may be elevated secondary to increased tubular urea resorption
- check serum K+ for hyperkalemia with severe azotemia
- urinary indices & urinary Na+ are variable
- urine sediment is generally without significant cellular elements
- proteinuria is generally absent
- evaluation of serum & urine electrolytes with post-obstructive diuresis
Radiology
- renal ultrasound to delineate hydronephrosis*
- include bladder ultrasound to assess post-void residual volume
- computed tomography (CT) may be helpful
- when results of ultrasound are equivocal
- retroperitoneal fibrosis
- periureteral metastatic disease
- avoid radiographic contrast (CT urography) with acute renal failure[5]
- 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
- relieve obstruction, monitor input & output - foley catheter
- fluid restriction if euvolemic or volume overloaded
- 1 to 1.5 L/day
- postobstructive diuresis may occur after relief of obstruction
- prognosis is good if obstruction is relieved within 1-2 weeks of onset, but tubular defects may persist
- little recovery may be expected if high-grade obstruction exceeds 3 months
- also see urinary retention
More general terms
More specific terms
Additional terms
References
- ↑ 1.0 1.1 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
- ↑ 3.0 3.1 Prescriber's Letter 11(1):3 2004 Detail-Document#: http://prescribersletter.com/(5bhgn1a4ni4cyp2tvybwfh55)/pl/ArticleDD.aspx?li=1&st=1&cs=&s=PRL&pt=3&fpt=25&dd=200105&pb=PRL (subscription needed) http://www.prescribersletter.com
- ↑ 4.0 4.1 NEJM Knowledge+ Question of the Week. July 17, 2018 https://knowledgeplus.nejm.org/question-of-week/1216
- ↑ 5.0 5.1 NEJM Knowledge+ Nephrology/Urology