Percutaneous Nephrolithotomy (PCNL)
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Management of nephrolithiasis through percutaneous techniques is most often reserved for stones greater than 1.5 cm to 2.0 cm, in a staghorn configuration, behind a stenosed infundibulum, in a calyceal diverticulum, in a kidney with ureteropelvic junction obstruction, or in anomalous kidneys (Figure 1). Stone-free rates for non-staghorn renal stones approach 95% with PCNL as compared to 85% with ureteroscopy and 75% with ESWL. For staghorn renal calculi, stone free rates reach 78% with PCNL and 54% with ureteroscopy. PCNL has largely replaced open and laparoscopic surgery in the management of complex and large renal stones. Compared to open surgery, PCNL allows patients quicker convalescence, less morbidity, and decreased cost.
Figure 1: Percutaneous nephrolithotomy (PCNL) is a percutaneous procedure for management of renal calculi. Generally, a rigid nephroscope is utilized. The two most common indications for PCNL are renal stones >2cm in size and staghorn calculi. (image generated using drawMD for iPAD: www.drawMD.com)
Because bacteria form biofilm on stone surfaces, even patients with sterile urine cultures and staghorn or infectious calculi must be treated with appropriate antibiotics for approximately two weeks prior to the procedure. Pre-operative broad spectrum antibiotics must also be given prior to the beginning of each procedure (please see AUA Best Practice Statement: (http://www.auanet.org/content/media/antimicroprop08.pdf ). Thoughtful use of pre-operative imaging affords delineation of anatomy and quantification of stone burden.
Absolute contraindications to PCNL include uncorrected coagulopathy and an active, untreated urinary tract infection. Any coagulopathy must be correct and infections treated prior to proceeding with PCNL.
Positioning and Room Setup
At many centers, the patient arrives in the operating room with percutaneous access—generally a small nephroureteral catheter placed by interventional radiology that affords entry access to the ureter through the desired calyx . Some urologists obtain percutaneous access themselves at the time of the procedure. Positioning is one of the most critical aspects of the procedure. The patient is intubated supine on the stretcher on which they entered the operating room. The patient is then “flipped” prone onto the operating room table. To cushion the patient’s ventral surface, either gel pads or pillows can be used. A foam face rest should be used to keep the patient’s head and neck in line with the rest of the body and keep the ET tube secure. Make sure the patient is centered on the table, as an off-center patient can make using the C-arm difficult. The upper extremity on the side of the procedure should be placed in a modified “superman” position as it prevents the surgeon from excessive leaning on the patient’s upper extremity during the procedure. The angle at the axilla should be 90O or less to prevent brachial plexus injury. The angle at the elbow should be 90O or greater. The contralateral upper extremity can be placed at the patient’s side. In male patients, be sure the patient is not laying on his genitalia. The legs should be in normal anatomic position and the feet and ankles should be padded (Figure 2).
Figure 2: Patient with a right nephroureteral access catheter placed prone on the operating room table in preparation for PCNL.
At this point bring in the C-arm and get it appropriately positioned. It is best to have the fluoroscopic view box next to the endoscopic view box to maximize efficiency (Figure 3)
Figure 3: Standard arrangement of operating room equipment for right-sided PCNL.
After prepping and draping (Figure 4), make sure to set up all of your cables and instruments in an organized fashion. The light cords, camera cords, and lithotripter cords should all be set up prior to beginning the procedure. Also, the nephroscope should be set up and placed on the patient’s dorsal surface so that it is readily available when needed.
Figure 4: Appearance of the surgical field after appropriate prepping and draping.
Figure 5 demonstrates the scout fluoroscopic image of a typical PCNL case. In this particular instance, a retrograde external ureteral catheter is seen in the renal pelvis in addition to the usual 5-French open-ended antegrade nephroureteral access catheter that had been placed by interventional radiology. External retrograde stenting is at times necessary in order to facilitate antegrade access by injecting contrast into the retrograde catheter. Such access is especially important when the stone burden is radiolucent. As such, effective communication between the urology and interventional radiology services is paramount during pre-operative planning.
Figure 5: Initial scout image at start of procedure (see text for details). Most urologists orient the image to correspond to the patient’s position on the OR table to facilitate live radiographic interpretation.
Step 1: Under fluoroscopic guidance, a wire is passed into the percutaneous nephroureteral access catheter, down the ureter and into the bladder. The access catheter is removed, leaving only the wire.
Step 2: An 11-blade scalpel is used to incise the skin approximately 1.5 cm. A second wire must then be placed down the ureter. This can be done with a dual lumen access catheter or a wide caliber catheter that is often included in the dilator set. One wire should be secured as a safety wire.
Step 3: The next step is to dilate the fascia so the nephroscopic sheath can be placed into the collecting system. This can be achieved either with rigid dilators or a balloon dilator. The surgeon should not dilate more than 1-2 cm past the inner edge of the
renal parenchyma to prevent injury to the renal pelvis and/or hilum. The rigid dilators create a working tract by sequentially upsizing the dilators over the working wire. Once the 30 French dilator is inserted, the working sheath is placed over the dilator into the collecting system. In modern practice, rigid dilators have largely been replaced by high-pressure nephrostomy tract balloon dilators. The non-compliant balloon radially dilates the tract at extremely high pressures (up to ~17 atm). The surgeon places the balloon over a wire into the renal pelvis (be certain, the balloon is not in the UPJ!) and inflates the balloon with contrast, watching for “waist” of the fascia to dissipate (Figure 6). Once the tract is dilated, the working sheath is advanced over the balloon into the renal pelvis (Figure 7).
Step 4: At this point, a nephrostogram should be done to confirm placement of access sheath. Once placement is confirmed, some physicians will remove the working wire, while some will leave it in place for duration of procedure (Figure 7).
Figure 6: Fluoroscopic image demonstrating a balloon dilator filled with contrast. The fascial “waist” is no longer present and the 30 French access sheath is ready to be passed into the collecting system over the balloon.
Figure 7: Fluoroscopic image demonstrates a working sheath in kidney with 2 wires passing down the UPJ into the ureter.
Step 5: Introduce the nephroscope into the sheath and visually examine the collecting system. Identify and assess stone burden (Figure 8). Irrigation during PCNL should be an isotonic solution (generally, normal saline) to prevent dilutional hyponatremia
secondary to venous uptake. Employing hypotonic irrigants such as water can be lethal. Irrigation fluid should be kept between 60cm-80cm above the patient to prevent excessive intrapelvic pressures and pyelocaliceal backflow.
Step 6: Fragment stones as necessary and remove them from collecting system. There are a variety of tools used for removing stones. These include tricep forceps, alligator forceps, and stone baskets. Generally the stone is too large to simply remove
through the access sheeah and fragmentation is necessary. Several types of lithotripters are commonly utilized (Link to lithotripter article). A pneumatic lithotripter uses mechanical force to break the stone by acting like a small jackhammer (Figure 9). An ultrasonic lithotripter uses ultrasound waves to fragment calculi. Modern devices often couple a suction port with the device to keep the stone in close proximity to probe and to remove pulverized fragments. Laser lithotripters also can be employed for stone fragmentation (see link for discussion of laser settings).
Figure 8: View of renal calculus through nephroscope.
Figure 9: Pneumatic lithotripter (metallic probe at bottom of image) is a common tool used to pulverize renal stones during PCNL.
Step 7: Once the stones have been fragmented, the residual stone debris should be removed. At times it is not possible to access all calyces with rigid instruments and a flexible nephroscope/cystoscope can be used through the access sheath to assess for presence of residual stone fragments. If residual fragments remain, a basket or a 3- pronged grasping forceps should be used to either remove the fragments or manipulate them into a location within reach of rigid instruments (Fig. 10).
Step 8: Thorough visual and fluoroscopic inspection must be used to insure stonefree status (Fig. 11).
Figure 10: 3-prong grasping forceps being used through a flexible nephroscope to grasp a stone in a calyx that could not be reached by rigid nephroscopy.
Figure 11: Calyx free of stone on visual examination.
Step 9: Once the stones burden is treated, generally a nephrostomy tube is placed into the collecting system either via the access sheath or over the safety wire. Contrast is injected and its position is confirmed fluoroscopically. Some physicians at times will also leave a catheter across the UPJ to facilitate secondary procedures if necessary. So called “tubeless” PCNLs have gained popularity. Only a double JJ stent is left in the urinary system and the parenchymal tract is filled with a cellulose-based hemostatic agent (Fig. 12).
Figure 12: Schematic demonstrating drains following a “tubeless” PCNL. The percutaneous track is generally filled with a cellulose-based hemostatic agent and a JJ stent is left in place to fascilitate antegrade drainage. (image generated using drawMD for iPAD: www.drawMD.com)
PCNL is an invasive surgical procedure. Patients must be thoroughly counseled on its possible complications. These include but are not limited to: sepsis, urine leak, perinephric hematoma, splenic injury, bowel injury, liver injury, pneumothorax, hydrothorax, hemothorax, hemorrhage, and pseudoaneurysm. The complication rate ranges from 1.1%-7%.
Andrew Harris, MD
Cheif Resident, University of Pennsylvania