Spontaneous passage depends on stone size, shape, location, and associated ureteral edema (which is likely to depend on the length of time that a stone has not progressed). Ureteral calculi 4–5 mm in size have a 40–50% chance of spontaneous passage. In contrast, calculi >6 mm have a <5% chance of spontaneous passage. This does not mean that a 1-cm stone will not pass or that a 1- to 2-mm stone will always pass uneventfully.
The vast majority of stones that pass do so within a 6-week period after the onset of symptoms. Ureteral calculi discovered in the distal ureter at the time of presentation have a 50% chance of spontaneous passage, in contrast to a 25% and 10% chance in the mid- and proximal ureter, respectively.
B. DISSOLUTION AGENTS
The effectiveness of dissolution agents depends on stone surface area, stone type, volume of irrigant, and mode of delivery. Oral alkalinizing agents include sodium or potassium bicarbonate and potassium citrate. Extra care should be employed in patients susceptible to congestive heart failure or renal failure. Citrate is metabolized to bicarbonate and comes in a variety of preparations.
Polycitra contains potassium and sodium citrate and citric acid. Bicitra contains only sodium citrate and citric acid. Food does not alter the effectiveness of these agents. Alternatively, orange juice alkalinizes urine. Intravenous alkalinization is effective with one-sixth molar sodium lactate.
Figure 16–15. A: Scout abdominal radiograph demonstrating large left staghorn renal calculus. B: Nuclear scintigraphic evaluation of renal calculi. Posterior view demonstrating uptake on large left staghorn calculus after furosemide (Lasix) diuresis. Note right kidney with uptake in lower pole. C: Follow-up tomogram confirms calculus (arrow) in right lower pole missed on initial radiograph.
Intrarenal alkalinization may be performed successfully under a low-pressure system (<25 cm water pressure). This may be achieved through a percutaneous nephrostomy tube or an externalized retrograde catheter.
A manometer, similar to those used for central venous pressure monitoring, is cheap, available, and practical.
Agents include sodium bicarbonate, 2–4 ampules in 1 L of normal saline, producing a urinary pH between 7.5 and 9. Tromethamine-E and tromethamine can produce urinary pHs of 8–10.5 and are especially effective with pH-sensitive calculi as in uric acid and cystine lithiasis.
Cystine calculi can be dissolved with a variety of thiols, including D–penicillamine (0.5% solution), N–acetylcysteine (2–5% solution), and alpha-mercaptopropionylglycine (Thiola) (5% solution).
Struvite stone dissolution requires acidification and may be achieved successfully with Suby’s G solution and hemiacidrin (Renacidin). Urinary pH may get down to 4.
Hemiacidrin must be used with sterile urine and careful monitoring of serum magnesium levels is required. The Food and Drug Administration has not approved hemiacidrin for upper-tract irrigations, and thus appropriate informed consent is required.
C. RELIEF OF OBSTRUCTION
Urinary stone disease may result in significant morbidity and possible mortality in the presence of obstruction, especially with concurrent infection. A patient with obstructive urinary calculi with fever and infected urine requires emergent drainage. Retrograde pyelography to define upper-tract anatomy is logically followed by retrograde placement of a double-J ureteral stent.
On occasion such catheters are unable to bypass the offending calculus or may perforate the ureter. In such situations one must be prepared to place a percutaneous nephrostomy tube.
D. EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY
Extracorporeal shock wave lithotripsy has revolutionized the treatment of urinary stones. The concept of using shock waves to fragment stones was noted in the 1950s in Russia. However, it was during the investigation of pitting on supersonic aircraft that Dornier, a German aircraft corporation, rediscovered that shock waves originating from passing debris in the atmosphere can crack something that is hard. It was the ingenious application of a model developed in hopes of understanding such shock waves that ESWL emerged.
The first clinical application with successful fragmentation of renal calculi was in 1980. The HM–1 (Human Model–1) lithotriptor underwent modifications in 1982 leading to the HM–2 and, finally, to the widespread application of the HM–3 in 1983 (Figure 16–16). Since then, thousands of lithotriptors have been put into use around the world, with millions of patients successfully treated.
All require an energy source to create the shock wave, a coupling mechanism to transfer the energy from outside to inside the body, and either fluoroscopic or ultrasonic modes, or both, to identify and position the calculi at a focus of converging shock waves. They differ in generated pain and anesthetic or anesthesiologist requirements, consumable components, size, mobility, cost, and durability.
Focal peak pressures (400–1500 bar), focal dimensions (6 x 28 mm to 50 x 15 mm), modular design, utilization to help increase mobility of frozen joints, varied distances (12–17 cm) between focus 1 (the shock wave source) and focus 2 (the target), and purchase price differentiate the various machines available today.
1. Shock wave physics–
In contrast to the familiar ultrasonic wave with sinusoidal characteristics and longitudinal mechanical properties, acoustic shock waves are unharmonic and have nonlinear pressure characteristics.
There is a steep rise in pressure amplitude that results in compressive forces (Figure 16–17). There are 2 basic types of shock wave sources: supersonic and finite amplitude emitters.
Supersonic emitters release energy in a confined space, thereby producing an expanding plasma and an acoustic shock wave. Such shock waves occur in nature-the familiar thunderstorm with lightning (an electrical discharge) followed by thunder (an acoustic sonic boom) is an analogous situation. Under controlled conditions, such an acoustic shock wave can successfully fragment calculi. The initial compression wave travels faster than the speed of sound in water and rapidly slows down to that speed. The traveling pressure wave is reduced in a nonlinear fashion.
Medical applications have focused such waves to concentrate energy on a calculus (Figure 16–18).
Finite amplitude emitters, in contrast to point source energy systems, create pulsed acoustic shock waves by displacing a surface activated by electrical discharge. There are 2 major types of finite amplitude emitters: piezoceramic and electromagnetic. The piezoceramic variety results in a shock wave after an electrical discharge causes the ceramic component to elongate in such a manner that the surface is displaced and an acoustic pulse is generated. Thousands of such components placed on the concave side of a spheric surface directed toward a focus result in high stress, strain, and cavitation pressures (Figure 16–19). Electromagnetic systems are similar in concept to a stereo speaker system.
An electrical discharge to a slab, adjacent to an insulating foil, creates an electric current that repulses a metal membrane, displacing it and generating an acoustic pulse into an adjacent medium. These waves need to be focused toward the offending stone.
All shock waves, despite their source, are capable of fragmenting stones when focused. Fragmentation is achieved by erosion and shattering (Figure 16–20). Cavitational forces result in erosion at the entry and exit sites of the shock wave. Shattering results from energy absorption with stress, strain, and shear forces. Surrounding biologic tissues are resilient because they are not brittle nor are the shock waves focused on them.
2. Preoperative evaluation–
Physical examination should be as thorough as in preparation for any other surgical procedure. Vital signs including blood pressure should be noted. Body habitus including any gross skeletal abnormalities, contractures, or excessive weight (>300 lb) may severely limit or preclude ESWL.
Borderline individuals require simulation before treatment. Pregnant women and patients with large abdominal aortic aneurysms or uncorrectable bleeding disorders should not be treated with ESWL. Individuals with cardiac pacemakers should be thoroughly evaluated by a cardiologist. If ESWL is contemplated, a cardiologist with thorough knowledge and with the ability to override the pacemaker should be present in the lithotripsy suite.
3. Intraoperative considerations–
a. Stone localization-Proper patient positioning is a prerequisite for successful lithotripsy. Palpating the patient’s ribs and pelvic bony girdle can approximate appropriate positioning. Anterior located kidneys, medial oriented portions of a horseshoe kidney, or transplant kidneys are best treated in the prone position. Understanding positioning options with the various lithotriptors available today is required to optimize therapy.
Small or poorly calcified calculi can be difficult to image with fluoroscopy, irrespective of their location. Placing a ureteral catheter identifies known anatomy and supplies an injection port for radiocontrast agents. A poorly calcified caliceal calculus can be identified by injecting dilute contrast agents into the collecting system and then focusing on the appropriate calyx or filling defect. In patients who cannot have retrograde stents placed, intravenous contrast agents may be used to help localize and thus focus on such stones.
b. Fluoroscopic imaging-The conditions for fluoroscopic imaging include appropriate collimation, dimmed room lighting, and adequate bowel preparation to decrease bothersome bowel gas and thus decrease radiation exposure and improve the quality of the fluoroscopic image.
Intermittent fluoroscopy reveals movement of calculi with respiration and is helpful in locating and focusing on offending calculi.
c. Ultrasonic imaging-Ultrasound localization has the advantage of eliminating radiation exposure to the patient or the lithotripsy team. There are 2 basic types: the coaxial unit, aligned with the shock wave generator, and the articulating arm unit with a mobile transducer. Ultrasound can easily identify radiolucent or small calculi that are difficult to visualize with fluoroscopy. However, ureteral or other medially located calculi may be difficult or impossible to identify, especially in nonobstructive collecting systems.
Visualization may be difficult or impossible with obese patients. Proficiency in ultrasound localization and assessment of fragmentation has a longer learning curve than that of fluoroscopy. Ultrasound images may be confusing when multiple stones or stone fragments are present.
d. Coupling-Successful fragmentation requires effective coupling. Coupling devices should have properties similar to those of human skin. Optimal systems should prevent pain, ecchymoses, hematomas, or skin breakdown.
Interfaces between gas and tissue can result in tissue damage. Air bubbles entrapped by hair, by bandages from prior percutaneous procedures, or by inadequately degassed fluid, or air in coupling cushions can significantly impede directed shock waves and result in skin ecchymoses or breakdown. Despite adequate coupling, fragmentation may be inadequate owing to refraction and reflection of shock waves at tissue interfaces, especially with obese patients.
Water bath provides good coupling. Submersion of patients can result in profound hemodynamic changes including peripheral venous compression resulting in increased right atrial pressure, increased pulmonary capillary wedge pressure, and increased cardiac index. These hemodynamic changes should be appreciated and appropriate monitoring should be used in individuals with marginal cardiovascular reserve.
In contrast, water cushion coupling systems have decreased water demands. A coupling gel like those used with ultrasonography provides an excellent interface with skin. The volume of such water cushions can frequently be adjusted to help focus calculi when patients are either extremely thin (eg, children) or obese. Very small patients may require an interposed bag (1–3 L) of normal saline to help with coupling. Both water coupling systems require degassed water to decrease water bubbles.
e. Shock wave triggering-Triggering shock waves with the electrocardiogram was originally performed to decrease cardiac dysrhythmias. The lithotriptor would sense the large swing of the QRS complex and initiate the shock wave 20 ms later; this would decrease shock waves during the repolarization phase of the cardiac cycle (myocardium is most sensitive during this time). If cardiac dysrhythmias occur, interruption of the procedure frequently stops them. However, if they continue, standard medical therapy is effective. Conceptually, it makes more sense to trigger the shock waves in response to the respiratory cycle to optimize accurate focusing on the offending calculi that move with respiratory motion. Such systems are available.
Many lithotriptors are now triggered without electrocardiogram gating and with unusual associated cardiac dysrhythmias. This can speed up therapy, especially in those with slow heart rates that are not amenable to pharmacologic manipulation.
f. Fragmentation-Safe shock wave dosage is unknown. Shock waves induce trauma, including intrarenal and perirenal hemorrhage and edema, and thus the minimal shocks needed to achieve fragmentation should be given. Casual overtreatment should be avoided since long-term complications are not yet known.
Determination of adequate fragmentation during treatment may be difficult. Initial sharp edges become fuzzy or blurred and have a shotgun-blast-like appearance. Stones that were initially visualized may disappear after successful fragmentation. Intermittent visualization ensures accurate focusing and assessment of progress and eventual termination of the procedure.
Bilateral nephrolithiasis may be treated in the same setting. One must first approach the side that is symptomatic or potentially more troublesome. If there is uncertainty concerning a large stone burden, one or more double-J catheters should be placed to decrease the likelihood of bilateral obstruction.
4. Postoperative care–
Patients should be encouraged to maintain an active ambulatory status to facilitate stone passage. Gross hematuria should resolve during the first postoperative week. Fluid intake should be encouraged.
Follow-up in approximately 2 weeks for discussion and evaluation of a KUB and renal ultrasonography will help assess success of fragmentation and passage of gravel.
Patients may return to work as soon as they feel comfortable in doing so.
Abdominal pain may be related to the shock waves.
Severe pain unresponsive to routine intravenous or oral medications should alert the physician for possible rare (0.66%) perirenal hematomas. In such a situation, CT should then be undertaken to stage the injury.
The potential association of ESWL with the development of hypertension has not been substantiated. Longterm data are still being collected.
Stone burden correlates with postoperative complications. Steinstrasse (stone street) or columnation of stone gravel in a ureter can be frustrating. It should be specifically ruled out when postoperative radiographs are evaluated.
Asymptomatic individuals can be followed up with serial KUBs and ultrasonography. Severe pain or fever requires intervention. Percutaneous nephrostomy drainage is usually uncomplicated owing to the associated hydronephrosis. Decompressing the collecting system allows for effective coaptation of the ureteral walls and encourages resolution of the problem. It is only in the rare patient that steinstrasse does not resolve with the procedures outlined; such cases require retrograde endoscopic manipulations to relieve the obstructed stone fragments.
Usually one finds 1 or 2 relatively large fragments that are obstructing. With their removal the columnation of fragments resolves.
Patients with large renal pelvic calculi (>1.5 cm) have a stone-free rate at 3 months approximating 75%, in comparison with those with a similar stone in a lower calyx, which approximates only 50%. Patients with small renal pelvic stones (<1.5 cm) have approximately a 90% stone-free rate in comparison to those with similar stones in a middle calyx (approximately 75%) or lower calyx (approximately 70%). Lower calyceal stone-free rates are increased with a small stone burden, a short and wide infundibulum, and a nonacute infundibulo-pelvic angle. Overall, approximately 75% of patients with renal calculi treated with ESWL become stone-free in 3 months. As stones increase in size, stone-free rates decrease, more so in the lower and middle calyces than in superior calyceal and renal pelvic locations.
E. URETEROSCOPIC STONE EXTRACTION
Ureteroscopic stone extraction is highly efficacious for lower ureteral calculi. The use of small-caliber ureteroscopes and the advent of balloon dilation or ureteral access sheaths have increased stone-free rates dramatically. Even relatively large-caliber endoscopes without balloon dilation are effective in lower ureteral stone retrieval.
Stone-free rates range from 66% to 100% and are dependent on stone burden and location, length of time the stone has been impacted, history of retroperitoneal surgery, and the experience of the operator. Complication rates range from 5% to 30%; the rates increase when manipulations venture into the proximal ureter. Ureteral stricture rates are <5%.
Postoperative vesicoureteral reflux is extremely rare. Calculi that measure <8 mm are frequently removed intact. Round wire stone baskets can be torqued to help entrap stone or stone fragments. Flat wire baskets should be used with caution; if twisted, they can develop sharp, knifelike edges resulting in ureteral injury. Excessive force with any instrument in the ureter may result in ureteral injury.
A variety of lithotrites can be placed through an ureteroscope, including electrohydraulic, solid and hollow-core ultrasonic probes, a variety of laser systems, and pneumatic systems such as the Swiss lithoclast.
Electrohydraulic lithotrites have power settings as high as 120 V that result in a cavitation bubble, followed by collapse of this bubble causing subsequent shock waves. Care should be taken to keep the tip of the electrode away from surrounding tissue and the tip of the endoscope. Ultrasonic lithotrites have a piezoceramic energy source that converts electrical energy into ultrasonic waves in the range of 25,000 Hz. This vibratory action is effective in fragmenting calculi. Hollow probes can suction stone fragments and debris simultaneously. Laser systems are discussed elsewhere in this book.
The electromechanical impactors are similar to jackhammers with a movable piston-like tip that fragments calculi.
F. PERCUTANEOUS NEPHROLITHOTOMY
Percutaneous removal of renal and proximal ureteral calculi is the treatment of choice for large (>2.5 cm) calculi; those resistant to ESWL; select lower pole calyceal stones with a narrow, long infundibulum and an acute infundibulo-pelvic angle; and instances with evidence of obstruction; the method can rapidly establish a stone-free status.
Needle puncture is directed by fluoroscopy, ultrasound, or both, and is routinely placed from the posterior axillary line into a posterior inferior calyx.
Superior caliceal puncture may be required, and in such situations care should be taken to avoid injury to the pleura, lungs, spleen, and liver. Tract dilation is performed by sequential plastic dilators (Amplatz system), telescoping metal dilators (Alken), or balloon dilation with a backloaded Amplatz sheath. Tracts placed during open renal procedures are frequently tortuous and suboptimal for subsequent endourologic procedures.
Percutaneous extraction of calculi requires patience and perseverance. Hardcopy radiographs help to confirm a stone-free status. Remaining calculi can be retrieved with the aid of flexible endoscopes, additional percutaneous puncture access, follow-up irrigations, ESWL, or additional percutaneous sessions. Realistic goals should be established. Patients should be informed that complex calculi frequently require numerous procedures.
Maintenance of body temperature with appropriate blankets during preoperative patient positioning and with warmed irrigation fluids helps to prevent bleeding diatheses associated with hypothermia. The average blood loss during a percutaneous nephrolithotomy is 2–2.8 g/dL of hemoglobin. Multiple percutaneous punctures and renal pelvic perforations are associated with a greater blood loss.
Overall, such procedures are safe and effective and have a transfusion rate well <10%.
The morbidity of the incision, the possibility of retained stone fragments, and the ease and success of less invasive techniques have made these procedures relatively uncommon when instruments and surgical experience are available. It is mandatory to obtain a radiograph before the incision is made; calculi frequently move. A variety of incisions to access the kidney are available.
Inspection with flexible endoscopes helps ensure a stone free status. Multiple, small renal pelvic calculi and difficult to-access caliceal calculi can be retrieved with the aid of a coagulum. Coagulum was initially produced from pooled human fibrinogen. The risks of hepatitis and other viral infections have made this method unacceptable. Cryoprecipitate can be obtained from rapid freezing of plasma.
Autologous plasma may be used to decrease the incidence of bloodborne infections. The tensile strength of cryoprecipitate is approximately 10 times that of a blood clot.
Injected into the renal pelvis, endogenous clotting factors result in a Jelly-like coagulum of the collecting system.
Small stones are entrapped and removed with the coagulum. A variety of Randall stone forceps help gain access into most of the collecting system.
I. ANATROPHIC NEPHROLITHOTOMY
Anatrophic nephrolithotomy is used with complex staghorn calculi. A complete staghorn calculus is a cast of the renal pelvis and calyces (Figure 16–21). A partial staghorn calculus involves the renal pelvis and extends into at least 2 infundibula. To gain access to the entire collecting system, a longitudinal incision is made on the convex surface of the kidney just posterior to the line of Brödel, taking advantage of the converging anterior and posterior renal blood supplies. Occlusion of the renal artery followed by renal cooling with slushed ice gives a relatively bloodless surgical field. A nerve hook is helpful to tease out calculi.
Careful inspection of the entire collecting system helps remove all stones. Repair of narrowed infundibula helps reduce stone recurrence rates. The collecting system is closed followed by the renal capsule. Intraoperative placement of a nephrostomy tube for possible follow-up irrigations or endoscopic inspection or stone retrieval makes hemostasis difficult. Open stone surgery becomes progressively more difficult after the first procedure owing to reactive scar tissue.
J. RADIAL NEPHROTOMY
Radial nephrotomy gives access to limited calyces of the collecting system. An appropriate approach to localized calculi, it is frequently used in blown-out calyces with thin overlying parenchyma. Intraoperative ultrasound helps to localize the calyx and the calculi. Once the kidney has been opened, the introduction of air can make interpretation of subsequent ultrasound scans confusing. A shallow incision of the renal capsule can be followed by puncture into the collecting system. Brain retractors provide excellent exposure.
Care should be taken not to force stones through narrow infundibula. Stones may be cut with heavy Mayo scissors, and remaining fragments can be retrieved. Inspection with flexible endoscopes is helpful. Intraoperative radiographs help document a stone-free status.
Caution should be taken with a simple nephrectomy even with a normal contralateral kidney, as stones are frequently associated with a systemic metabolic defect that may recur in the contralateral kidney. What may seem prudent and simple today may be regretted tomorrow.
Other unusual procedures include ileal ureter substitution performed with the hope of decreasing pain with frequent stone passage. Autotransplantation with pyelocystostomy is another option for patients with rare malignant stone disease.
Long-standing ureteral calculi-those inaccessible with endoscopy and those resistant to ESWL-can be extracted with ureterolithotomy. Again, a preoperative radiograph documents stone location and directs an appropriate incision.
The proximal ureter may be approached with a dorsal lumbotomy. An incision lateral to the sacrospinalis muscles allows medial retraction of the quadratus lumborum. The anterior fascicle of the dorsal lumbar fascia must be incised to gain proper exposure despite the appearance of potentially opening the peritoneum. Once the ureter is identified, a vessel loop or a Babcock clamp should be placed proximal to the stone to prevent frustrating stone migration. Extension of this incision is limited superiorly by the 12th rib and inferiorly by the iliac crest. A longitudinal incision over the stone with a hooked blade exposes the calculus. The nerve hook is excellent to help tease out the stone. A flank or anterior abdominal muscle splitting incision gives excellent exposure to mid- and distal ureteral stones.
Marshall L. Stoller, MD
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