Postrenal Acute Renal Failure
Postrenal acute renal failure can only occur if both urinary outflow tracts are obstructed or the outflow tract of a solitary kidney is obstructed. The condition is most often due to obstruction of the lower urinary tract.
Patients with severe oliguria or anuria (output of less than 100 mL of urine per day) are likely to have postrenal acute renal failure However, not all patients with postrenal acute renal failure are oliguric.
The primary causes of postrenal acute renal failure include prostatic hypertrophy, prostate cancer, cervical cancer and retroperitoneal disorders. Intratubular causes include crystals (e.g., urate) and myeloma light chains.3
One of the first evaluation steps in most patients with acute renal failure is to determine whether a patient has postrenal acute renal failure, because treatment is frequently relatively easy and the potential for recovery of renal function is often inversely related to the duration of obstruction.3Bladder catheterization may be diagnostic and therapeutic in patients with bladder or urethral obstruction.
Hydronephrosis detected on renal ultrasound examination is the major signal that obstruction is present. For the detection of obstruction, ultrasonography has a sensitivity of 90 percent and a specificity that approaches 100 percent.14False-negative ultrasound examinations can occur if the obstruction is very early or retroperitoneal fibrosis is present.
In patients with postrenal acute renal failure, treatment efforts are directed at the underlying disease. Treatments available for various causes include bladder catheterization, percutaneous nephrostomy, lithotripsy, ureteral stenting and urethral stenting.