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by urinary tract obstruction, has been extensively studied in animal models but clinical studies on this subject are outdated, and/or have focused on the mechanisms of 'post-obstructive diuresis' (POD), a potentially life-threatening polyuria that can develop after the release of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.