TYPES OF NEPHROSTOMY TUBES	Section 5 of 11
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Currently, most interventionalists use 2 main types of nephrostomy tubes. Both of these types have an end that is secured in the renal pelvis by locking the distal portion of the tube. The types are the following:

• Pigtail (locking-loop or Cope-loop) catheter: The locking loop of the catheter is formed within the renal pelvis by tugging gently on the internal suture and locking the catheter in place.

• Malecot (tulip-shaped) catheter: The catheter tip slightly retracts so that the tulip portion is larger than the tube diameter. These catheters are mainly used when the renal pelvis is small because of the patient's size or when a large staghorn calculus is present.

	PREPROCEDURAL EVALUATION	Section 6 of 11
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The following steps are included the preprocedural evaluation performed prior to percutaneous nephrostomy tube placement at the Medical College of Virginia. (This list is not all-inclusive, and the preprocedural preparation at other centers may differ.)

• Obtain informed consent from the patient, next of kin, or healthcare proxy.

• Order laboratory studies, including determination of prothrombin time (PT), activated partial thromboplastin time (aPTT), platelet count, BUN and creatinine levels, hematocrit (Hct) and hemoglobin (Hgb) levels, WBC count, and urinalysis and urine culture results.

• Review pertinent images (eg, sonograms, CT scans, intravenous urograms [IVUs], radionuclide scintigrams) to assess the location of the colon, liver, and spleen in determining the approach.

• Establish intravenous access and adequately hydrate the patient.

• Administer prophylactic antibiotics 60 minutes prior to the procedure, especially if pyonephrosis is suspected or if the obstruction is due to a renal calculus. The use of antibiotics is somewhat controversial; however, in patients with a known urinary tract obstruction, antibiotics should be administered prior to the procedure (preferably 1 h prior to puncture) and continued for at least 24 hours after the procedure. Antibiotics should be chosen on the basis of urine culture results, if available. If the results are not available, use of a broad-spectrum antibiotic is recommended.

• The patient should receive nothing by mouth (NPO) for 4-8 hours prior to the procedure, for conscious sedation precautions.

• Some have advocated the placement of percutaneous nephrostomy tubes without performing preprocedural coagulation studies, although we disagree with this philosophy unless the situation is an absolute emergency. Since the kidney is highly vascular, needle puncture and tract dilation in a patient with a coagulopathy could result in massive hemorrhage.

	PROCEDURE	Section 7 of 11
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Guidance and selection of access system

After the preprocedural evaluation, an appropriate approach or guidance is chosen. In most cases, guidance involves sonography, although conventional fluoroscopy or CT (ie, CT fluoroscopy) can be used. Once guidance is determined, the access system is selected. Many are available today. Common access systems include a micropuncture set (Cook, Bloomington, Ind), the Accustick introduction system (Medi-Tech/Boston Scientific, Watertown, Mass) or a Hawkin needle. The first two are 21- and 22-gauge needle systems, while the Hawkin needle is 18 gauge. Under sonographic guidance, the first two systems are more difficult to visualize than the Hawkin needle; however, the risk of bleeding is significantly less with the smaller-gauge needle.

Procedure

The patient is commonly placed in a prone or prone-oblique position; the side to be punctured is elevated. The region should be evaluated with sonography, CT, or fluoroscopy, and the site marked. This region should then be prepared (eg, cleansed with Betadine solution) and draped in the usual manner. The patient is given an appropriate medication for conscious sedation (eg, fentanyl and Versed) and a local anesthetic, usually 1% lidocaine to anesthetize the skin. A small skin nick is made to facilitate passage of the needle into the skin.

Puncture site selection is crucial in minimizing the risk of hemorrhage. The best route for needle entry into the renal collecting system is through an oblique posterolateral approach along the Brödel line and into the end of a posterior calix. This line is near the posterior axillary line and is about 2-3 cm below the 12th rib. A percutaneous nephrostomy tract that approaches along Brödel line has the smallest risk of causing substantial arterial injury and subsequent hemorrhage.

The needle is angled toward a posterior lower or middle pole calix. Once the needle is inserted into the calix and into the collecting system, the stylet is removed, and urine is returned if an obstruction is present. If no urine is present, a few maneuvers can be used. A 10-mL syringe should be attached to the needle hub, and the needle and syringe should be retracted slightly. If urine is aspirated, the tip is likely within the collecting system. Otherwise, a 0.018-in platinum-tipped wire can be used to probe the region, or a small amount of contrast agent can be injected to check the position.

After the collecting system is accessed, urine sample can be obtained and sent for routine culture and sensitivity testing. Contrast material should be gently injected into the collecting system to confirm the location. Overdistension of the system with contrast material or the withdrawal of too much urine for culturing should be avoided, because these can cause bacterial seeding or difficulty in gaining access if the wire is inadvertently lost. In commonly practice, the amount of contrast agent used inject is the same as the amount of urine removed.

	DISCUSSION	Section 9 of 11
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Percutaneous nephrostomy tube placement is most commonly used in urinary decompression due to obstruction. Technical success is achieved in more than 95% of cases, with proper training. Images often demonstrate the level and cause of obstruction; however, at the time of tube placement, the cause of obstruction may not be known. Often, the ureteral obstruction is acute and caused by ureteral calculi or traumatic ureteral injury. The obstruction can have a chronic cause, such as caused urothelial malignancy or extrinsic compression due to bleeding or neoplasm.