Editing Pathophysiology of Urinary Tract Obstruction (section)

=== Renal drainage ===
* Ureteral obstruction that is symptomatic, accompanied by fever, complicated by undrained infection, or determined to be high grade, bilateral, or inducing renal failure warrants immediate drainage.
* Urine cultures should be obtained from the obstructed renal unit at the time of relief of obstruction when infection is suspected, and antibiotic therapy should be instituted.
** If thick purulent fluid is obtained from the kidney at the time of ureteral stenting, a large-diameter stent should be placed
* '''Both percutaneous nephrostomy tubes and internal stents have been shown to be equally effective in relieving an obstructed collecting system with similar complication rates'''
** '''Advantages of percutaneous nephrostomy tubes (5):'''
**# '''Superior drainage, especially if the fluid is more purulent, due to larger caliber'''
**# '''Ability to irrigate to prevent clogging'''
**# '''Urine output of the kidney can be measured'''
**# '''Excessive ureteral manipulation can be avoided, decreasing the risk for sepsis or rupture'''
**# '''Can be done using US guidance with local anesthesia and conscious sedation, eliminating the need for an anesthesiologist and ionizing radiation exposure'''
** '''Advantages of internal stents (2):'''
**# '''Increased patient comfort'''
**# '''Lower potential risk for bleeding complications'''; should be considered first for patients that are coagulopathic.
** '''Internal stent placement typically requires greater x-ray exposure than percutaneous nephrostomy placement, which may be of concern in pregnant patients,''' and accelerated stent encrustation in pregnant patients may increase the risk for stent failure.
** '''Historically, ureteral stenting has not been very effective for treating patients with extrinsic ureteral obstruction.'''
*** New metallic stents composed of a unique continuous unfenestrated coil of nonmagnetic alloy have proved to be safe and effective for patients with extrinsic compression of the ureter and offer longer indwelling times (3.5 to 11 months).
* '''The duration and severity of obstruction has a significant influence on renal functional recovery.'''
** In a canine model, recovery of renal function after UUO:
*** 7 days: 100%
*** 14 days: 70%
*** 4 weeks: 30%
*** 6 weeks: 0%
** More recent studies demonstrate that renal damage can persist despite recovery of renal function.
** '''In humans, delayed relief of obstruction (>2 weeks) has been demonstrated to decrease long-term renal function and increase the risk for hypertension'''
** Factors that have a positive influence on functional recovery include:
**# Smaller degree of obstruction
**# Greater compliance of the collecting system
**# Presence of pyelolymphatic backflow
**# Early relief of obstruction
** Predictors of diminished recovery of renal function
**# Older age
**# Decreased renal cortical thickness
* '''In general, a nephrectomy should be considered for an obstructed kidney that contributes <10% to the patient’s overall renal function.'''
* '''After relief of obstruction, patients with BUO or an obstructed solitary kidney should be monitored for the development of post-obstructive diuresis'''
** There is a profound diuresis and an increase in sodium excretion after relief of bilateral ureteral obstruction. This is due to ANP and, perhaps reduced sodium transporters. The massive natriuresis enhances excretion of phosphate, potassium, and magnesium.
*** '''ANP increases GFR by promoting dilation of the afferent arteriole and constriction of the efferent arteriole'''. It also decreases the sensitivity of tubuloglomerular feedback, inhibits renin release, and increases the ultrafiltration coefficient.