Post-obstructive diuresis: a review

Acute Kidney Injury Caused by Obstructive Nephropathy

Acute kidney injury secondary to obstructive nephropathy is a frequent event that accounts for 5 to 10% of all acute kidney injury cases and has a great impact on the morbidity and mortality in those affected. The obstruction in the urinary tract has a profound impact on kidney function due to damage produced by ischemic and inflammatory factors that have been associated with intense fibrosis. This pathology is characterized by its effects on the management of fluids, electrolytes, and the acid-base mechanisms by the renal tubule; consequently, metabolic acidosis, hyperkalemia, uremia, and anuria are seen during acute kidney injury due to obstructive nephropathy, and after drainage, polyuria may occur. Acute urine retention is the typical presentation. The diagnosis consists of a complete medical history and should include changes in urinary voiding and urgency and enuresis, history of urinary tract infections, hematuria, renal lithiasis, prior urinary interventions, and constipation. Imaging studies included tomography or ultrasound in which hydronephrosis can be seen. Management includes, in addition to drainage of the obstructed urinary tract system, providing supportive treatment, correcting all the metabolic abnormalities, and initiating renal replacement therapy when required. Although its recovery is in most cases favorable, it seems to be an undervalued event in nephrology and urology. This is because it is mistakenly believed that the resolution and recovery of kidney function is complete once the urinary tract is unobstructed. It can have serious kidney sequelae. In this review, we report the epidemiology, incidence, pathophysiological mechanisms, diagnosis, and treatment of acute kidney injury due to obstructive nephropathy.

Factors associated with postobstructive diuresis following decompressive surgery with placement of ureteral stents or subcutaneous ureteral bypass systems for treatment of ureteral obstruction in cats: 37 cases (2010-2014)

OBJECTIVE

To describe postobstructive diuresis (POD) in cats undergoing surgical placement of ureteral stents or subcutaneous ureteral bypass systems for treatment of ureteral obstruction in cats and to identify factors associated with duration and maximum severity of POD.

DESIGN

Retrospective case series.

ANIMALS

37 client-owned cats with ureteral obstruction treated between August 2010 and December 2014.

PROCEDURES

Medical records were reviewed, and data extracted included signalment, history, results from physical examinations and clinical laboratory analyses, treatment, urine output, and outcome. Data were evaluated to identify factors associated with POD duration and maximum severity, alone or in combination.

RESULTS

Serum concentrations of creatinine, potassium, phosphorus, and BUN before surgery positively correlated with duration and maximum severity of POD. Absolute changes in serum concentrations of creatinine, potassium, and BUN from before surgery to after surgery positively correlated with POD duration. Cats with anuria before surgery had longer POD than did other cats; however, there was no difference in POD duration or maximum severity with unilateral versus bilateral ureteral obstruction. Thirty-four of 37 (92%) cats survived to hospital discharge, which was not associated with whether ureteral obstruction was unilateral or bilateral. Azotemia resolved in 17 of the 34 (50%) cats that survived to hospital discharge.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of the present study indicated that several factors were associated with POD duration and maximum severity, alone or in combination, and that with intensive management of fluid and electrolyte derangements, regardless of the extent of the original azotemia, a high percentage of cats survived to hospital discharge.

Controversies in the management of feline urethral obstruction

OBJECTIVE

To discuss areas of differing opinion in the management of feline urethral obstruction and present current evidence to either support or refute common practices.

ETIOLOGY

Urethral obstruction may occur as a result from a functional obstruction (idiopathic obstruction) or a physical obstruction, such as mucous plugs or calculi within the urethra. Potential risk factors for obstruction in cats include predominantly indoor status, decreased water intake, and increased body weight.

DIAGNOSIS

The diagnosis is most commonly made based on history and initial physical exam-straining to urinate, vocalizing, signs of systemic illness, moderate to large firm bladder on abdominal palpation.

THERAPY

Treatment is based on available evidence. The type of IV isotonic crystalloid used does not seem to matter and rate should be determined by need for fluid resuscitation, and replacement of deficit and ongoing losses. Though controversial, cystocentesis appears to be safe and may offer some benefits in initial management. There is evidence to suggest a smaller urethral catheter (3.5 Fr) may be associated with decreased risk of reobstruction. Routine use of antimicrobial agents in hospital is not recommended; they should be dispensed based on culture performed at the time of catheter removal. Though commonly used, evidence in support of antispasmodics is limited and further prospective investigation is needed.

PROGNOSIS

Feline urethral obstruction is associated with 90-95% survival, with reported recurrence rates of 15-40%. Potential factors affecting recurrence include size or duration of indwelling urinary catheter, use of antispasmodic agents, patient age, and indoor-outdoor lifestyle; however, different studies offer conflicting results. Increased water intake and environmental modification do seem to decrease risk of recurrence.

Severe post-renal acute kidney injury, post-obstructive diuresis and renal recovery

Study Type--Therapy (case series) Level of Evidence 4. What's known on the subject? and What does the study add? The pathophysiology of post-renal acute kidney injury (PR-AKI), i.e. caused by urinary tract obstruction, has been extensively studied in animal models but clinical studies on this subject are outdated, and/or have focused on the mechanisms of 'post-obstructive diuresis' (POD), a potentially life-threatening polyuria that can develop after the release of obstruction. In severe PR-AKI, the risk of occurrence of POD is high. POD occurrence predicts renal recovery without the persistence of severe chronic kidney failure. In the present study, the occurrence of POD and the persistence of chronic renal sequelae could be predicted early from clinical variables at admission before the release of obstruction.

OBJECTIVE

• To identify predictors of post-obstructive diuresis (POD) occurrence or severe chronic renal failure (CRF) persistence after the release of urinary tract obstruction in the setting of post-renal acute kidney injury (PR-AKI).

PATIENTS AND METHODS

• Bi-centre retrospective observational study of all patients with PR-AKI treated in two intensive care units (ICUs) from 1998 to 2010. • Clinical, biological and imaging characteristics on admission and after the release of obstruction were analysed with univariate and, if possible, multivariate analysis to search for predictors of (i) occurrence of POD (diuresis >4 L/day) after the release of obstruction; (ii) persistence of severe CRF (estimated glomerular filtration rate <30 mL/min/1.73 m(2), including end-stage CRF) at 3 months.

RESULTS

• On admission, median (range) serum creatinine was 866 (247-3119) µmol/L. • POD occurred in 34 (63%) of the 54 analysable patients. On admission, higher serum creatinine (Odds ratio [OR] 1.002 per 1 µmol/L, 95% confidence interval [CI] 1.000-1.004, P = 0.004), higher serum bicarbonate (OR 1.36 per 1 mmol/L, 95% CI 1.13-1.65, P < 0.001), and urinary retention (OR 6.96, 95% CI 1.34-36.23, P = 0.01) independently predicted POD occurrence. • Severe CRF persisted in seven (21%) of the 34 analysable patients, including two (6%) cases of end-stage CRF. Predictors of severe CRF persistence after univariate analysis were: lower blood haemoglobin (P < 0.001) and lower serum bicarbonate (P = 0.03) on admission, longer time from admission to the release of obstruction (P = 0.01) and absence of POD (P = 0.04) after the release of obstruction.

CONCLUSIONS

• In severe PR-AKI treated in ICU, POD occurrence was a frequent event that predicted renal recovery without severe CRF. • POD occurrence or severe CRF persistence could be predicted early from clinical and biological variables at admission before the release of obstruction.

Obstructive polyuric renal failure following renal transplantation

In a previously nephrectomized patient with a well functioning renal allograft, acute renal failure with massive polyuria and hypertension developed. Relief of a periureteric obstruction resulted in rapid correction of all three. Pathogenesis of hypotonic polyuria is thought to be a defect in the collecting duct permeability to water, stimulating nephrogenic diabetes insipidus. Normal urinary dilution and acidification suggest intact function of the ascending loop of Henle and distal convoluted tubules. The quick reversal of polyuria and renal failure after obtaining relief of the obstruction suggest that both the decrease in the glomerular filtration rate and tubular dysfunctions are due to functional changes in the nephron rather than to organic damage, a possibility also borne out by the findings in a renal biopsy specimen showing normal glomeruli and intact tubular epithelial cells. Ureteric obstruction should be considered in any patient with renal failure and polyuria; it may be a correctable cause of hypertension.