URINARY TRACT OBSTRUCTION

 

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Urinary Tract Obstruction

BASICS

DEFINITION
Restricted flow of urine from the kidneys through the urinary tract to the external
urethral orifice

Pathophysiology
Excess resistance to urine flow through the urinary tract develops because of lesions affecting the excretory pathway. This causes an increase in pressure in the urinary space proximal to the obstruction and may cause abnormal distention of this space with urine. Pathophysiologic consequences ensue depending on the site, degree, and duration of obstruction. Complete urinary obstruction causes pathophysiologic state equivalent to oliguric acute renal failure. Perforation of the excretory pathway with extravasation of urine is functionally equivalent to urinary tract
obstruction.

Systems Affected
• Renal/Urologic
• Gastrointestinal, cardiovascular, nervous, and respiratory systems as uremia develops

SIGNALMENT
More common in males than females

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SIGNS

Urinary Signs
• Bladder neck or urethral obstruction
• Pollakiuria (common)
• Stranguria
• Reduced velocity or caliber of the urine stream or no urine flow during voiding
• Gross or microscopic hematuria
• Palpable distention of the urinary bladder that is excessive (i.e., overly large or turgid) or inappropriate (i.e., remains after voiding efforts)
• Uroliths often palpated in the urethras of obstructed male dogs
• Ureteral obstruction
• Occasionally, palpable renomegaly is discovered in an animal with chronic partial ureteral obstruction, especially when the lesion is unilateral.

Extraurinary Signs
• Signs of uremia develop when urinary tract obstruction is complete (or nearly complete): lethargy, dull attitude, reduced appetite, vomiting, dehydration
• Signs of severe uremia: weakness, hypothermia, bradycardia with moderate hyperkalemia, high rate of shallow respirations, stupor or coma, seizures may occur terminally, tachycardia resulting from ventricular dysrhythmias induced by severe hyperkalemia
• Signs of perforation of the excretory pathway: leakage of urine into the peritoneal cavity causes abdominal pain and distention; leakage of urine into periurethral spaces causes pain and swelling in intrapelvic or perineal tissues, depending on the site of the urethral injury; fever

CAUSES

Intraluminal Causes
• Solid or semi-solid structures including uroliths, urethral plugs in cats, blood clots, and sloughed tissue fragments
• The most common site of urinary tract obstruction is the urethra.
• Urolithiasis is the most common cause of urethral obstruction in male dogs.
• Urethral plugs are the most common cause of urethral obstruction in male cats.

Intramural Causes
• Neoplasia of the bladder neck or urethra is a common cause of urinary obstruction, particularly in dogs.
• Pyogranulomatous inflammatory lesions in the urethra are seen occasionally in dogs.
• Fibrosis at a site of a previous injury or inflammation can cause stricture or stenosis, which may impede urine flow or may be a site where intraluminal debris becomes lodged.
• Prostatic disorders in male dogs
• Edema, hemorrhage, or spasm of muscular components can occur at sites of intraluminal (e.g., urethral) obstruction and contribute to persistent or recurrent obstruction to urine flow after removal of the intraluminal material. Tissue changes might develop because of injury inflicted by the obstructing material, by the manipulations used to remove the obstructing material, or both.
• Ruptures, lacerations, and punctures of the excretory pathway are usually caused by traumatic
incidents.

Miscellaneous Causes
• Displacement of the urinary bladder into a perineal hernia
• Neurogenic (see Urinary Retention, Functional)

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RISK FACTORS
• Urolithiasis, particularly in males
• Feline lower urinary tract disease, particularly in males.
• Prostatic disease in male dogs

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS
• Repeated, unproductive squatting in the litterbox by a cat that has a urethral obstruction can be misinterpreted as constipation.
• Animals whose efforts to urinate are not observed by their owners can be examined because of signs referable to uremia without a history of possible obstruction.
• Evaluation of any patient with azotemia should include consideration of possible postrenal causes (e.g., urinary obstruction). See Creatinine and Blood Urea Nitrogen (BUN)--Azotemia and Uremia for differential diagnosis of this problem.
• Animals with a ruptured urinary bladder can exhibit clinical signs (e.g., anorexia, vomiting, diarrhea, depression, lethargy, weakness, and collapse) and laboratory test results (azotemia, hyperkalemia, and hyponatremia) similar to that commonly seen in patients with hypoadrenocorticism (Addison's disease).
• Once urinary obstruction is recognized, diagnostic efforts focus on detecting the presence and evaluating the magnitude of abnormalities secondary to obstruction, and identifying the location, cause, and completeness of the impediment(s) to urine flow.

CBC/BIOCHEMISTRY/URINALYSIS
• Results of a hemogram are usually normal, but a stress leukogram may be seen.
• Biochemistry analysis reveals azotemia, hyperphosphatemia, metabolic acidosis, and hyperkalemia proportional to the degree and duration of the obstruction.
• Hematuria and proteinuria are common. Crystalluria supports a diagnosis of urolithiasis and atypical epithelial cells may be seen in patients with neoplasia.

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OTHER LABORATORY TESTS
Uroliths that are passed or retrieved should be sent for crystallographic analysis to determine their composition.

IMAGING

Radiography
• Uroliths are often demonstrated by survey radiography; however, some are difficult or impossible to see because of their size, composition, or location.
• Positive-contrast urethrography is the most sensitive method of detecting intraluminal and intramural lesions of the urethra, and double-contrast cystography is the most sensitive method of detecting lesions of the bladder lumen and wall.
• Upper urinary tract (i.e., ureter or renal pelvis) obstruction can be detected by excretory urography if renal function is adequately preserved on the affected side(s) so that the radiographic contrast media is excreted and sufficiently concentrated to be seen proximal to the obstruction.

Ultrasonography
Ultrasonography is highly sensitive for detecting lesions of the bladder and proximal urethra (including the prostate gland in male dogs) and upper urinary tract (i.e., ureter or renal pelvis) obstruction.

OTHER DIAGNOSTIC PROCEDURES
• Electrocardiography may detect abnormalities secondary to hyperkalemia including tall T waves, prolonged PR interval, and bradycardia
• Urinary catheterization has diagnostic and therapeutic value. As the catheter is inserted, the location and nature of obstructing material may be determined. Some or all of the obstructing material (e.g., small uroliths and feline urethral plugs) may be induced to pass out of the urethra distally for identification and analysis. Retrograde irrigation of the urethral lumen may propel intraluminal debris toward the bladder. Although intramural lesions sometimes are detected during catheterization, catheter insertion can be normal. Animals that cannot urinate despite generating adequate intravesical pressure (i.e., have excessive outlet resistance) and have urethras that can be readily catheterized and irrigated either have intramural lesions or functional urinary retention.
• Cytologic evaluation of specimens obtained from the urinary tract with the assistance of catheters may be diagnostic, particularly for carcinoma of the urethra or bladder and some prostatic diseases.
• Prostatic massage or physical manipulation of the catheter tip positioned near the suspected lesion is used to produce cell-rich specimens that are retrieved through the catheter by aspiration or washing with saline in an attached syringe.
• Cystoscopy can be helpful, particularly in female dogs with intramural lesions of the bladder neck or urethra.

TREATMENT
• Complete urinary tract obstruction is a medical emergency that can be life-threatening; treatment should be started immediately
• Partial urinary obstruction is not necessarily an emergency; however, animals with partial obstruction may be at risk for developing complete obstruction. Partial obstruction can cause irreversible urinary tract damage if not treated promptly.
• Treat as an inpatient until the animal's ability to urinate has been restored.
• Surgery is sometimes required to relieve obstruction
• Long-term management and prognosis depend on the cause of the obstruction.
• Treatment has three major components: combating the metabolic derangements associated with postrenal uremia (e.g., dehydration, hypothermia, acidosis, hyperkalemia, and azotemia); restoring and maintaining a patent pathway for urine outflow; and implementing specific treatment for the underlying cause of urine retention.

MEDICATIONS

DRUGS AND FLUIDS
• Fluid therapy is indicated in patients with dehydration or azotemia. Give fluids intravenously if systemic derangements are moderately severe or worse. Lactated Ringer's solution is the fluid of choice, except for patients with severe hyperkalemia (i.e., > 8.0 mEq/L and/or ECG changes), in which the fluid of choice is 0.45% saline and 2.5% dextrose solution with addition of sodium bicarbonate (1-2 mEq/kg slow bolus). Cardiotoxic effects of hyperkalemia that are immediately life-threatening should be combated by giving calcium gluconate (2-10 ml 10% solution IV slowly to effect). As soon as hyperkalemia and its effects have abated, lactated Ringer's solution should be used.
• Procedures for relief of obstruction often require or are facilitated by giving sedatives or anesthetics. When substantial systemic derangements exist, fluid administration and other supportive measures should be started first. Careful decompression of the bladder by cystocentesis may be performed before anesthesia and catheterization. The dosage of sedative or anesthetic drug should be calculated by the low end of the recommended range or given only to effect. Isoflurane is the anesthetic of choice; however, satisfactory results can be obtained with a variety of other anesthetic or sedatives.

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CONTRAINDICATIONS
Intramuscular ketamine should be avoided in patients with complete obstruction, because it is excreted through the kidneys. If the obstruction can not be eliminated, prolonged sedation will result.

PRECAUTIONS
Drugs that reduce blood pressure or induce cardiac dysrhythmia should be avoided until dehydration or hyperkalemia are resolved.

POSSIBLE INTERACTIONS None

ALTERNATE DRUGS
Normal saline with added dextrose (2.5% IV) is an alternative fluid choice for patients with dehydration and hyperkalemia.

FOLLOW-UP

PATIENT MONITORING
• Check urine production and hydration status frequently; adjust fluid administration rate accordingly.
• Verify ability to urinate adequately or use urinary catheterization to combat urine retention. Indwelling catheterization with closed drainage is appropriate if catheter insertion requires chemical restraint or is unduly traumatic, but frequent brief catheterization is a better choice if catheter insertion can readily be done repeatedly (e.g., as in some male dogs).
• When the ECG indicates life-threatening changes, continuous monitoring is needed initially to guide treatment and evaluate response.

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POSSIBLE COMPLICATIONS
• Death
• Injury to the excretory pathway while trying to relieve obstruction
• Hypokalemia during postobstruction diuresis
• Recurrence of obstruction

MISCELLANEOUS

ASSOCIATED CONDITIONS
• Bradycardia secondary to hyperkalemia
• Azotemia, hyperphosphatemia, and metabolic acidosis

AGE RELATED FACTORS
In old dogs, the underlying cause of obstruction (e.g., tumor and prostate disease) often is difficult to treat effectively.

ZOONOTIC POTENTIAL N/A

PREGNANCY N/A

SYNONYMS Urethral obstruction

Author George E. Lees

http://emedicine.medscape.com/article/438890-overview

Urinary Tract Obstruction

Author: Edward David Kim, MD, FACS, Professor of Surgery, Division of Urology, University of Tennessee Graduate School of Medicine; Consulting Staff, University of Tennessee Medical Center
Coauthor(s): Yvonne Katherine P Koch, MD, Physician, Department of Urology, Case Western Reserve University, University Hospitals of Cleveland; Suzette E Sutherland, MD, Adjunct Associate Professor, Department of Urologic Surgery, University of Minnesota Medical School; Metro Urology, Centers for Continence Care and Female Urology
Contributor Information and Disclosures

Updated: Oct 31, 2008

Introduction

Urinary tract obstruction is a common problem encountered by urologists, primary care physicians, and emergency medicine physicians. Urinary tract obstruction can occur at any point in the urinary tract, from the kidneys to the urethral meatus. It can develop secondary to calculi, tumors, strictures, and anatomical abnormalities. Obstructive uropathy can result in pain, urinary tract infection, loss in renal function, or, possibly, sepsis or death. Thus, suspected cases of urinary tract obstruction merit consultation with a urologist for evaluation.

History of the Procedure

Relief of urinary tract obstruction dates back to the time of Hippocrates with the use of the urethral catheter. The first catheters were made of metal; by the Middle Ages, more flexible catheters were developed. Rubber catheters were developed in the 19th century. Today, various sizes, compositions (eg, latex, silicone), and tips (coude, straight, council tip) of catheters are available.

Suprapubic access to the bladder can be traced back to the 16th century. It was initially considered a procedure of last resort but was refined in the 20th century. Today, it is a fairly common mode for relief of urinary tract obstruction.

Problem

Urinary tract obstruction impedes urine flow. This obstruction causes distention of the urinary tract proximal to the point of obstruction. The distention is caused by increased pressure and can result in pain, which may be the first sign of obstruction. Distortion of the urinary tract and renal failure can develop; the severity depends on the degree and duration of obstruction. When the urinary tract is obstructed, urine stasis can occur, predisposing to urine infection.

Frequency

In an autopsy series of 59,064 patients aged 0-80 years, the frequency of hydronephrosis was 3.1%. In women with uterine prolapse, hydronephrosis occurs in approximately 5% with first-degree prolapse and in 40% with third-degree prolapse. In women, hydronephrosis is more likely develop during the third to seventh decade of life secondary to pregnancy and gynecologic malignancies. In men, hydronephrosis is most likely after age 60 years secondary to prostatic obstruction. Hydronephrosis is found in 2-2.5% of children.

Etiology

Obstruction of urinary flow can occur anywhere from the kidneys to the urethral meatus. Certain points along this path are more susceptible to obstruction. The three points of narrowing along the ureter include the ureteropelvic junction (UPJ), the crossing of the ureter over the area of the pelvic brim (the iliac vessels), and the ureterovesical junction (UVJ).

In women, an additional area of ureteral narrowing can occur as the distal ureter crosses posterior to the pelvic blood vessels and the broad ligament in the posterior pelvis. Women can also experience urinary tract obstruction when the ureters become externally compressed by pelvic tumors or by advanced cervical or gynecologic malignancies.

More commonly in older women, prolapse of pelvic structures, such as the uterus and bladder, can lead to urinary tract obstruction. In younger women, pregnancy can cause urinary tract obstruction secondary to ureteral obstruction from the gravid uterus.

In men, the enlarged prostate (benign prostatic hypertrophy) can cause urinary tract obstruction by obstructing the urethra. Urethral stricture can also lead to urinary tract obstruction.

Both men and women can experience urinary tract obstruction from calculi, strictures, or tumors (intrinsic or extrinsic). Obtaining a thorough history of present illness, medication history (eg, anticholinergics, narcotics), past medical history (diabetes, calculi, tumors, radiation, retroperitoneal fibrosis, neurologic disorders), and past surgical history (pelvic surgery, radiation) is helpful in identifying potential causes of obstruction. Individuals with neurogenic bladder or detrusor sphincter dyssynergia can also experience bladder outlet obstruction.

In children, obstruction may be more commonly due to UPJ or UVJ obstruction, ectopic ureter, ureterocele, megaureter, or posterior urethral valves. Prenatal screening with ultrasonography is important in early identification of obstruction. In addition, children with incontinence or urinary tract infection need a workup because they may also have some type of urinary tract obstruction.

Pathophysiology

Chronic urinary tract obstruction can lead to permanent damage to the urinary tract. Infravesical obstruction can lead to changes in the bladder, such as trabeculation, cellule formation, diverticula, bladder wall thickening, and, ultimately, detrusor muscle decompensation. Progressive back pressure on the ureters and kidneys can occur and can cause hydroureter and hydronephrosis. The ureter can then become dilated and tortuous, with the inability to adequately propel urine forward. Hydronephrosis can cause permanent nephron damage and renal failure. Urinary stasis along any portion of the urinary tract increases the risk of stone formation and infection, and, ultimately, upper urinary tract injury. Urinary tract obstruction can cause long-lasting effects to the physiology of the kidney, including its ability to concentrate urine.

Presentation

The clinical presentation of urinary tract obstruction varies with the location, duration, and degree of obstruction. Thus, a thorough history and physical examination are key in the patient evaluation.

Upper urinary tract obstruction (kidney, ureter) can manifest as flank pain, ipsilateral back pain, and ipsilateral groin pain. Nausea and vomiting are also common and usually occur in acute obstruction. Chronic obstruction is usually indolent and may be asymptomatic. When infection is present, the patient may experience fever, chills, and dysuria. Hematuria may also be present. When bilateral obstruction or unilateral obstruction in a solitary kidney is severe and renal failure is present, uremia can be present. Uremia symptoms include weakness, peripheral edema, mental status changes, and pallor. If hydronephrosis is severe, the kidney may be palpable on physical examination, especially in children. In cases that involve an infectious process, costovertebral angle tenderness can indicate pyelonephritis.

Lower urinary tract obstruction (bladder, urethra) can manifest as voiding dysfunction such as urgency, frequency, nocturia, incontinence, decreased stream, hesitancy, postvoid dribbling, and a sensation of inadequate emptying. Suprapubic pain or a palpable bladder indicates urinary retention. Infection may be present, and patients may experience dysuria. Hematuria may be present with or without infection.

Digital rectal examination can reveal prostatic enlargement, decreased rectal tone, or prostatitis. Urethral stricture often requires cytoscopy for diagnosis. Meatal stenosis is usually apparent on physical examination. Patients with urethral stricture may report a history of trauma, instrumentation, or sexually transmitted disease. They may also experience a split urinary stream. In women, the presence of uterine or bladder prolapse can be visualized on a pelvic examination. A urethral diverticulum can also be palpated on pelvic examination.

Indications

A patient with complete urinary tract obstruction; any type of obstruction in a solitary kidney; obstruction with fever, infection, or both; or renal failure needs immediate attention by a urologist. Patients with pain that is uncontrolled by oral medications or with persistent nausea and vomiting that causes dehydration also need immediate attention, as well as hospital admission.

Relevant Anatomy

Obstruction to urinary flow can occur anywhere from the kidneys to the urethral meatus. Certain points along this path are more susceptible to obstruction. The 3 points of narrowing along the ureter include the UPJ, the crossing of the ureter over the area of the pelvic brim at the level of the iliac vessels, and the UVJ.

Contraindications

Different procedures carry different relative and absolute contraindications. Prior to any elective surgical intervention, the urine should be sterile and all coagulation parameters should be normal.

In the setting of pelvic trauma with possible urethral disruption, some urologists advocate placement of a suprapubic catheter instead of a Foley catheter because a Foley catheter can worsen the urethral disruption, introduce infection into a pelvic hematoma, and worsen pelvic bleeding.

When dealing with a pregnant woman with an obstructed urinary tract, some urologists place a ureteral stent, while others prefer placement of a percutaneous nephrostomy tube.

When patients have had previous abdominal or pelvic surgery, some urologists may prefer placing an open suprapubic tube instead of a percutaneously placed tube for fear of bowel injury.

Workup

Laboratory Studies

• Urinalysis

  • Urinalysis can provide useful information in evaluating for infection or hematuria.

  • WBCs in the urine can indicate infection or inflammation.

  • Nitrite- or leukocyte esterase–positive urine indicates infection.

  • All urine that contains WBCs or is positive for nitrite or leukocyte esterase should be sent for culture analysis and antibiotic susceptibility.

  • RBCs in the urine can be present in infection, stones, or tumor. A urologist should evaluate all patients with microscopic or gross hematuria to ensure that malignancy is not present. These patients require urine cytology and a full hematuria workup (cystoscopy, upper urinary tract imaging).

  • Urine pH is useful in the evaluation and workup of stones.

• Basic metabolic panel

  • Renal insufficiency is detected on a basic metabolic panel based on elevated BUN and creatinine levels. This can result from bilateral renal obstructive processes or obstruction in a solitary kidney.

  • Other metabolic abnormalities can also be present in renal insufficiency. Hyperkalemia and acidosis may be present.

• Complete blood cell count

  • Leukocytosis indicates infection.

  • Anemia can be due to acute processes (eg, blood loss) or chronic processes (eg, chronic renal insufficiency, malignancy).

Imaging Studies

• Ultrasonography

  • Ultrasonography of the kidneys and bladder is a useful imaging modality as an initial study. It is a noninvasive inexpensive study that does not involve radiation exposure or depend on renal function. It is the initial study of choice in pregnant women.

  • In patients with intravenous pyelography (IVP) dye allergies or elevated creatinine levels, ultrasonography is a very useful source of imaging.

  • In children, this is often part of the initial workup for obstructive processes.

  • Ultrasonography is sensitive in revealing renal parenchymal masses, hydronephrosis, a distended bladder, and renal calculi.

  • The accuracy of this imaging modality depends heavily on the experience of the ultrasonographer.

  • In adults, if the ultrasonography findings are abnormal in any way, additional imaging is usually recommended. The combination of renal ultrasonography with flat-plate radiography of the kidneys, ureters, and bladder (KUB) is an inexpensive initial combination.

• Computerized tomography scan

  • A CT scan is very useful in providing anatomic detail and is often a first-line test in the evaluation of a patient.

  • A CT scan provides information regarding the urinary tract, as well as any possible retroperitoneal or pelvic pathologic condition that can affect the urinary tract via direct extension or external compression.

  • A noncontrast CT scan should be obtained to assess for calculi. If calculi are found, flat-plate radiography of the abdomen (KUB) should be obtained to help determine calcium content and stone shape and to assist in monitoring the progress of the stone. Its progress can be observed with periodic simple radiography.

  • A contrasted CT scan is needed to provide information on renal pathology.

  • If delayed contrast images are obtained, CT urography with 3-dimensional reconstruction can provide excellent visualization of the entire upper urinary tracts. A CT scan can be used to identify or rule out any other intra-abdominal processes that can cause presenting symptoms (eg, appendicitis, cholecystitis, diverticulitis, abdominal aneurysms, ovarian cysts).

• Intravenous pyelography

  • IVP involves the injection of dye into the venous system and a series of KUB radiographs over time.

  • It can be performed in patients with a normal creatinine value (<1.5 mg/dL) for visualization of the upper urinary tract.

  • It provides both anatomical and functional information.

  • Delayed calyceal filling, delayed contrast excretion, prolonged nephrography results, and dilatation of the urinary tract proximal to the point of obstruction characterize obstruction.

  • IVP is superior to CT scan in revealing small urothelial upper tract lesions.

  • If IVP is inadequate, retrograde pyelography can be performed to completely visualize the renal pelvis or ureter.

  • Patients with IVP dye allergy cannot undergo this test.

  • A combination CT scan and IVP (CT/IVP) test is commonplace. With this combined technique, both modalities can be used. CT urography, as mentioned above (see Computerized tomography scan), is also an excellent modality.

• Radionucleotide studies: A renal scan can be performed to determine the differential function of the kidneys, as well as to demonstrate the concentrating ability, excretion, and drainage of the urinary tract. Lasix can be administered with the renal scan to verify delayed excretion and the presence of obstruction.

• Magnetic resonance imaging

  • MRI is not a first-line test used to evaluate the urinary tract.

  • In patients who cannot tolerate a CT scan with contrast, an MRI with gadolinium can be performed to reveal any enhancing renal lesions.

  • MRI is useful in delineating specific tissue planes for surgical planning, as well as in evaluating the presence or extent of a renal vein or inferior vena cava thrombus in cases of renal tumors.

  • MRI does not reveal urinary stones well so is not often used as a first-line test.

• Retrograde urethrography: Radiographic dye is injected into the urethral meatus via Foley catheter at the distal urethra. Fluoroscopy is used to visualize the entire urethra for stricture or any abnormalities. This test can be particularly useful in working up lower urinary tract trauma.

• Retrograde pyelography: See Cystoscopy with retrograde pyelography.

• Nephrostography: This can be performed in patients who have a nephrostomy tube in place. Radiographic dye is injected antegrade through the nephrostomy tube. With fluoroscopy, any abnormalities or filling defects in the renal pelvis or ureter are visible. This can be safely performed even in patients with IVP contrast allergies.

Diagnostic Procedures

• Cystoscopy: Cystoscopy is the placement of a small camera called a cystoscope through the urethral meatus and passing through the urethra into the bladder. Any abnormalities in the urethra, prostatic urethra, bladder neck, and bladder can be visualized. This can be performed in the office or in the operating room.

• Cystoscopy with retrograde pyelography: Retrograde pyelography is performed in the operating room with a cystoscope in the bladder. Radiographic dye is injected into each ureteral orifice. Then, with the use of fluoroscopy, any ureteral or renal pelvis filling defects or abnormalities can be visualized. The contrast load does not interfere with renal function and can be used in patients with elevated creatinine levels. It can also be used in patients with an IVP dye allergy because the contrast remains extravascular.

Histologic Findings

When upper urinary tract obstruction occurs, the kidney undergoes interstitial fibrosis, with the accumulation of collagens and other extracellular matrix components.

Staging

No staging system exists for urinary tract obstruction.

Treatment

Medical Therapy

Consultation with a urologist should be obtained in patients with urinary tract obstruction, as in hydronephrosis or urinary retention. A patient with complete urinary tract obstruction; any type of obstruction in a solitary kidney; obstruction with fever or infection; or renal failure needs immediate attention by a urologist. Patients with pain that is uncontrolled with oral medications or with persistent nausea and vomiting that causes dehydration also need immediate urological attention.

A partial urinary tract obstruction in the absence of infection can be initially managed with analgesics and prophylactic antibiotics until a complete urologic evaluation is performed and definitive management is completed.

Antibiotics are often given for prophylaxis and should cover common urinary tract pathogens. Commonly used antibiotics include trimethoprim-sulfamethoxazole, nitrofurantoin, cephalosporins, and fluoroquinolones.

Pain secondary to urinary tract obstruction is often managed with oxycodone, hydrocodone, acetaminophen, and nonsteroidal anti-inflammatory medications.

Surgical Therapy

The goal of surgical intervention is to completely relieve the urinary tract obstruction. This can be evaluated with reimaging to ensure that the obstruction is resolved, as well as renal function monitoring with a creatinine laboratory test. The recovery of renal function depends on the severity and duration of the obstruction.

Different interventions can be performed to temporarily relieve the point of obstruction. Surgical intervention is usually obtained once the point of obstruction is identified with radiographic imaging.

Lower urinary tract obstruction (bladder, urethra) can be relieved with the following:

• Urethral catheter

  • A urethral catheter (size 8F-24F) is a flexible external catheter that extends from the bladder through the urethra.

  • A physician or nurse can place it. If catheter placement is difficult, a urologist may be needed to avoid urethral trauma. The urologist may need to perform urethral dilation, cystoscopy, or both to pass the catheter.

  • The catheter can be left indwelling, or, as an alternative, the patient can perform clean intermittent catheterization.

  • If blood is present at the urethral meatus after pelvic trauma and suspicion of urethral injury exists, a urologist should be consulted prior to catheter placement. Retrograde urethrography needs to be performed to rule out urethral injury.

• Suprapubic tube or catheter: If a Foley catheter cannot be passed, a suprapubic tube can be placed percutaneously (at the bedside) or in an open fashion (in the operating room). A suprapubic tube is placed on the lower anterior abdominal wall, approximately 2 finger-breadths above the pubic symphysis. Ultrasound guidance should be used for bedside procedures to ensure proper placement without injury to adjacent structures. In patients with previous abdominal surgery, adhesions and scar tissue may have changed the normal bowel location, so an open approach may be preferred.

Upper urinary tract obstruction (ureter, kidney) can be relieved with the following:

• Ureteral stent: A ureteral stent is a flexible tube that extends from the renal pelvis to the bladder. It can be placed during cystoscopy to relieve obstruction along any point in the ureter. A ureteral stent generally needs to be changed every 3 months.

• Nephrostomy tube: A nephrostomy tube is a flexible tube that is placed through the back directly into the renal pelvis. If a ureteral stent cannot be placed cystoscopically in a retrograde fashion, a percutaneous nephrostomy tube can be inserted for relief of hydronephrosis. If needed, a ureteral stent can then be passed in an antegrade fashion through the nephrostomy tube tract.

The following are urologic emergencies that require immediate attention and intervention:

• Complete urinary tract obstruction

• Any type of obstruction in a solitary kidney

• Obstruction with fever, infection, or both

• Renal failure

• Pain that is uncontrolled with oral medications

• Nausea and vomiting that causes dehydration

Preoperative Details

Before any surgical intervention or any manipulation of the urinary tract, broad-spectrum antibiotics should be initiated to prevent infection or urosepsis. Ideally, before any manipulation is performed, the urine should be sterile. However, this may not be possible in cases of emergent surgical intervention. Urine culture along with the administration of broad-spectrum antibiotics is important.

If cystoscopy and stent are needed emergently, coagulation is not a concern. If percutaneous drainage is necessary, coagulopathies should be corrected.

Intraoperative Details

Different interventions can be performed to temporarily relieve the point of obstruction. If the planned procedure cannot be performed safely or is not adequate in relieving urinary tract obstruction, other modes of urinary tract decompression can be tried.

Postoperative Details

When a patient has long-standing urinary tract obstruction that has been relieved, they may experience postobstructive diuresis.¹ This physiologic diuresis is usually self-limiting and can be managed conservatively with fluid replacement and, if needed, electrolyte replacement. Postobstructive diuresis is defined as diuresis of more than 200 mL/h for at least 2 hours. Patients with severe diuresis should receive intravenous fluid replacement in the form of half normal saline at 80% of the hourly urine volume for the first 24 hours, then 50%. Postobstructive diuresis usually lasts 24-72 hours. Most cases are not severe enough to require this level of attention.

Follow-up

Definitive treatment at the point of obstruction is needed after the acute obstruction is resolved. Adults and children often have different etiologies of urinary tract obstruction. Thus, various definitive surgical treatment options are available for each condition. After definitive treatment is achieved, a final imaging study is obtained to verify complete relief of the obstruction. The type of study performed, as well as the timing of the study, is left to the discretion of the urologist.

For excellent patient education resources, visit eMedicine's Kidneys and Urinary System Center. Also, see eMedicine's patient education articles Intravenous Pyelogram, Cystoscopy, Magnetic Resonance Imaging (MRI), and CT Scan.

Complications

A patient with urinary tract obstruction should see a urologist promptly because of the serious complications that the obstruction can impose. The following are complications of obstructive uropathy:

• Infection, including cystitis (bladder infection), pyelonephritis (kidney infection), abscess formation, and urosepsis

• Urinary extravasation with urinoma formation

• Urinary fistula formation

• Renal insufficiency or failure

• Bladder dysfunction secondary to a defunctionalized bladder

• Pain

Outcome and Prognosis

The prognosis of urinary tract obstruction depends on the cause, location, degree, and duration of obstruction, as well as the presence of a urinary tract infection. The longer the duration of obstruction, the greater the severity of obstruction, and the presence of a concomitant infection can lead to a worse prognosis. The prognosis is favorable if the renal function is normal, the infection is cleared, and the obstruction is relieved in a timely manner.

Future and Controversies

As time goes on, new procedures emerge and old procedures are modified to relieve urinary tract obstruction. In addition, with newer cameras and equipment and the use of laparoscopy, surgical intervention is becoming more advanced.

--
Shigenoi Haruki