Volume Expansion Enhances the Recovery of Renal Function and Prolongs the Diuresis and Natriuresis After Release of Bilateral Ureteral Obstruction: A Possible Role for Atrial Natriuretic Peptide

Obstructive uropathy: Overview of the pathogenesis, etiology and management of a prevalent cause of acute kidney injury

Obstructive uropathy is defined as the structural or functional interruption of urinary outflow at any level in the urinary tract. It is regarded as one of the most prevalent causes of acute kidney injury (AKI), accounting for 5%-10% of cases. Acute severe obstruction of the urinary tract is a potentially threatening situation for the kidneys and therefore requires prompt identification and management to relieve obstruction. The aim of the present article is to review and synthesize available evidence on obstructive uropathy, providing a clinical guideline for clinicians. A literature review on obstructive uropathy in the context of AKI was performed, focusing on the least clarified aspects regarding diagnosis and management. Recent literature searching was conducted in English and top-level evidence articles including systematic reviews, metanalyses and large series were prioritized. Acute obstruction of the urinary tract is a diagnostic and therapeutical challenge that may lead to important clinical complications together with direct structural and hemodynamic damage to the kidney. Early recognition of the leading cause and its exact location is essential to ensure prompt urinary drainage together with the most suitable drainage technique selection. A multidisciplinary approach, including urologists, nephrologists, and other medical specialties, is best suited to correctly manage concomitant hemodynamic changes, fluid and electrolyte imbalances, and other related issues. Obstructive uropathy is one of the leading causes of AKI. Recognition of patients suitable for early diversion and feasibility or adequate selection of the indicated technique is sometimes challenging. A thorough understanding of the physiopathology behind the development of urinary obstruction is vital for correct diagnosis and management.

Post-obstructive diuresis after posterior urethral valve treatment in neonates: a retrospective cohort study

BACKGROUND

The management of posterior urethral valve (PUV) in neonates requires close monitoring in the intensive care unit because of the risk of post-obstructive diuresis (POD). Our aim was to describe the incidence and factors associated with POD in newborns treated for PUV.

METHODS

Retrospective analysis of the medical records of all neonates who underwent surgical intervention for PUV in our neonatal intensive care unit between January 2014 and April 2021.

RESULTS

Of the 40 patients included, 15 (37.5%) had POD defined by urine output > 6 ml.kg-1.h-1 during the first 24 h following urinary tract obstruction relief. At prenatal ultrasound examinations, oligohydramnios was more common in the group with POD than in the group without (53.3% vs. 8%, p = 0.002). Preterm birth was more frequent in neonates with POD (66.7% vs. 8%; p < 0.001). Median serum creatinine (212 [137-246] vs. 95 [77-125] µmol.l-1; p < 0.001) and urea (8.5 [5.2-12.2] vs. 4.1 [3.5-4.7] mmol.l-1; p < 0.001) concentrations on the day of obstruction relief were significantly higher in the group with POD than in the group without. After adjustment for prematurity, logistic regression models confirmed correlation between the occurrence of POD and the severity of the consequences of urethral obstruction (i.e., oligohydramnios and serum creatinine levels; ß = 2.90 [0.88; 5.36], p = 0.013 and ß = 0.014 [0.003; 0.031], p = 0.034, respectively).

CONCLUSIONS

In neonates, POD is common after the relief of PUV-related obstruction. Our findings may help to identify patients at highest risk. A higher resolution version of the Graphical abstract is available as Supplementary information.

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.

RENAL RESPONSES TO ATRIAL NATRIURETIC PEPTIDE ARE PRESERVED IN BILATERAL URETERAL OBSTRUCTION AND AUGMENTED BY NEUTRAL ENDOPEPTIDASE INHIBITION

PURPOSE

Atrial natriuretic peptide (ANP) contributes to post-obstructive diuresis in bilateral ureteral obstruction (BUO). In this study we examined the activity of neutral endopeptidase (NEP), an enzyme responsible for degradation of ANP, in the kidney in rats subjected to BUO for 24 hours.

MATERIALS AND METHODS

Renal function was examined by the clearance method in sham operated rats and BUO rats after obstruction release. Renal responses to an intravenous bolus injection of ANP (5 microg/kg) were studied in sham operated and BUO rats with or without pretreatment with intravenous phosphoramidon (100 microg/kg per minute), a NEP inhibitor.

RESULTS

In BUO rats natriuresis and diuresis occurred despite a marked decrease in the glomerular filtration rate (GFR). ANP administration increased GFR and induced marked natriuresis and diuresis in sham operated and BUO rats. Inhibition of ANP degradation by phosphoramidon induced natriuresis and diuresis, and accentuated these renal responses to ANP.

CONCLUSIONS

Renal responses to ANP and renal NEP activity were preserved in 24-hour BUO. NEP inhibition to attenuate ANP degradation augmented responses to ANP in increasing GFR, natriuresis and diuresis. These findings provide the theoretical potential for facilitating the recovery of GFR after BUO release by inhibiting ANP degradation by pharmacological means.