Retrograde approach

The retrograde technique is the most simple and least invasive. It is done through a single ureteral catheter that is advanced beyond the level of the lesion or stone. The main disadvantage of this technique is the limitation of outflow through or around this small stent. This can result in a rapid elevation of intrapelvic pressures. Therefore, this technique of irrigation is not recommended. In an attempt to avoid this complication, Kuwahara and colleagues [5] used a computer‐controlled, pressure‐monitor intermittent pump (Figure 29.1a). This pump infuses fluid for 1 minute, holds for 30 seconds, and then drains for 9 seconds. If the pressure increases beyond the preset limit (15 cmH₂O), the infusion stops. If the pressure increase is sustained for 5 seconds, the drainage valve opens. This system was not widely used because it was prohibitively expensive; because of this, its safety and efficiency were not properly evaluated. Without such a pump, a single ureteral catheter for irrigation is not recommended.

Several other techniques of retrograde instillation have been described. One technique proposed by Dormia et al. [6] utilizes concentric catheters placed in the ureter to facilitate the outflow from the kidney into the bladder (Figure 29.1b). Another less‐efficient technique is by vesicoureteral reflux in a patient with an indwelling ureteral stent after ureteral meatotomy [7]. Recently, a high‐flow low‐pressure irrigation system was described that uses an 8 Fr pigtail catheter through a 12/14 Fr ureteral access sheath (Applied Medical Systems, Rancho Santa Margarita, CA, USA). In an in vitro study, this system was found to be associated with significantly higher flow rates and lower pressures when compared with a single nephrostomy tube without ureteral catheters [8].

Antegrade approach

The ideal inflow and outflow is achieved by percutaneous antegrade fashion through the use of two nephrostomy tubes. For example, two Malecot catheters (16 or 18 Fr) could be used (Figure 29.1c). This configuration is versatile and can be used in most patients. In patients with struvite stones, which tend to form large, irregular pieces on fragmentation, an endopyelotomy stent (14/8.2 Fr) provides excellent two‐way outflow, decreases the volume of fragments that enter the ureter and prevent its obstruction [9] (Figure 29.1d). Another method of preventing ureteral obstruction is insertion of an indwelling double pigtail catheter when two Malecot nephrostomy tubes are used. A simpler method of inflow and outflow in antegrade fashion through two nephrostomy sites is the use of a circular tube (Figure 29.1e).

Two coaxial techniques of irrigation have been described. Hare and McOmish [10] described a renal pelvic lavage set to irrigate different areas of the pelvis through a single nephrostomy site allowing both inflow and outflow (Figure 29.1f). Once the Teflon sheath is in place, an inner 6.3 or 8.3 Fr pigtail catheter is directed at the stone for inflow. Outflow, which is limited, occurs through the surrounding sheath and down the ureter. The second coaxial technique of irrigation works well for upper ureteral stones [11, 12]. It is set up by inserting either a 5 Fr ureteral or angiogram catheter over a wire through the lumen of an 18 Fr Foley catheter, which serves as a nephrostomy tube (Figure 29.1 g). The small inner catheter, which provides inflow, can be advanced so that its tip is adjacent to the stone, whereas the Foley catheter provides outflow. This is an effective method for dissolving upper ureteral stones. A simpler technique of irrigating the renal pelvis through a single nephrostomy site is the use of a three‐way Foley catheter [13].

Combined approach

One combination of both antegrade and retrograde techniques can be accomplished through the insertion of a percutaneous nephrostomy (NT) tube and ureteral catheter. The NT acts as an ideal outflow while the ureteral catheter is used for instillation (Figure 29.1 h). However, using the combination of a ureteral catheter, a urethral catheter and a nephrostomy tube severely decreases patient mobility. Therefore, a modified approach can use an NT to instill agents and an indwelling double pigtail ureteral catheter as a drainage catheter. The drawback of this approach is that there is much less efficient outflow through a ureteral catheter than a nephrostomy tube. Therefore, this modification would be ideal for small stones that dissolve in a short period of time, such as uric acid stones.

All the techniques described above should follow appropriate safety principles. Patients should have preoperative urine cultures and be treated with culture‐specific antibiotics. Urine cultures should be negative prior to initiating irrigation and patients should be kept on antibiotics throughout the irrigation. In addition, once the tubes are inserted, contrast studies should be performed 24 hours later to rule out extravasation. The irrigation should start slowly with warm saline at a rate of 30 ml/h. When the patient remains pain‐free and afebrile, the rate is doubled every 2–4 hours until the target rate of 120 ml/h is reached [13]. After 12–24 hours of saline irrigation, the active agent is instilled at a rate of 30 ml/h and increased sequentially to 120 ml/h. There are several advantages to warming the irrigation solution. It is more comfortable for the patient, it avoids hypothermia, and it may increase the effectiveness of therapy [14–16].

It is important to have an intrapelvic pressure‐monitoring system in all of the techniques described. If renal pelvic pressures are uncontrolled, pyelovenous and pyelolymphatic backflow leads to systemic absorption. Subsequently, the patient may suffer agent‐specific systemic toxicities or changes in serum chemistries when the irrigant solution is nontoxic [17]. The intrapelvic pressure should not be allowed to rise above 25 cmH₂O in order to prevent pyelovenous backflow [18]. The simplest method is the use of a central venous pressure (CVP) manometer connected to the inflow line. This is readily available and familiar to the nursing staff. Unfortunately, this is an open system that is prone to contamination or overflow spills. Furthermore, it requires continuous monitoring since there is no preset pressure alarm or automatic shutoff for high pressures (>15 cmH₂O). A better alternative is a closed continuous infusion pump that provides a continuous display of the intrapelvic pressure and will sound an alarm and shut off if the preset limit is exceeded (CareFusion, San Diego, CA, USA) [6]. Regardless of which pump is used, the patient should be taught how to immediately turn off the pump in case of flank pain or fever.

New concepts

Small‐caliber percutaneous instruments (SCPI) provide a new range of tools for kidney stone treatment. The impact of combined high‐pressure irrigation inflow and simultaneous sensor‐controlled suction on irrigation turnover and intrarenal pressure in SCPI was recently investigated. A 9.5 Fr Amplatz sheath was introduced through the lower calyx and an 8 Fr ureteric catheter was inserted through the ureter of a nonperfused porcine kidney. Another 8 Fr ureteric catheter was inserted through the upper calyx, and irrigation was performed using a pressure‐controlled, combined irrigation/suction pump. Analysis of the intrapelvic pressure was performed by different irrigation pressures with and without sensor‐controlled suction through the ureteric catheter [19]. After initiating irrigation flow, the intrarenal pressure reached a plateau within seconds without any pressure peaks during the whole experiment. This sensor‐controlled suction increased fluid turnover and decreased intrarenal pressure in SCPI. In addition, such a purging effect prevented collapse or hyperdistention of the collecting system, especially in small‐caliber instruments. However, SCPI has not been tested in humans yet.

Similarly, Colli et al. found that application of a 10 Fr ureteral dual‐lumen catheter in a porcine model produced adequate retrograde drainage with low intrarenal pressures at high infusion rates (up to 80 ml/min) [20]. This experiment supports the use of separate channels for inflow and outflow during retrograde infusion to maintain intrarenal pressures around 5 cmH₂O.

Nakamura et al. reported a novel constant‐pressure irrigation technique for a case of a left renal pelvic tumor which developed postradical cystectomy, right nephroureterectomy, and left ureterectomy in a patient with multiple urothelial tumors. The tumor was endoscopically ablated through a nephrostomy tract followed by mitomycin C irrigation [21]. The authors designed a novel constant‐pressure irrigation system for effective and safe irrigation into the closed‐space renal pelvis. Through a hole in the urinary drainage bag tube, a 5 Fr open‐ended ureteral catheter was inserted, and the tip of the catheter was kept at the tip of the nephrostomy tube. The ureteral drainage tube was placed 20 cm above the kidney level to continuously irrigate the renal pelvis with mitomycin C for six‐weekly treatments of 1 hour each time. The patient has been recurrence‐free for one year (Figure 29.1i).

Uric acid stones

Almost all individuals who form uric acid stones have persistently low urinary pH (<5.5) and most excrete normal amounts of uric acid [26, 27]. The acid–base properties of uric acid stones render them amenable to dissolution therapy. Uric acid is a weak organic acid with a pK_a of 5.35 in urine at 37 °C. At this pH, half is present as the undissociated acid and half as the urate anion. Since urate is more soluble than uric acid, raising the urinary pH within the physiological range has a profound effect on how much uric acid/urate can be dissolved. For example, a urine sample containing 800 mg/l total urate will have 600 mg/l uric acid at a pH of 5.0 but less than 100 mg/l at pH 6.5. The latter figure is well below the solubility limit of uric acid so that a solution above pH 6.5 can dissolve a uric acid calculus [18]. Any solution above pH 7 is likely to be effective but higher urinary pH solutions may have a tendency to calcify the stone, particularly if sodium bicarbonate is used as the base [28]. Increasing the urinary volume further enhances the therapeutic efficacy of alkaline medications [29]. In addition, decreasing the oral purine load from dietary sources can effectively help treat patients because 40– 60% of excreted uric acid is derived from exogenous sources. Regardless of the method chosen, urine pH should be monitored with pH strips to optimize therapy. Serum and urine uric acid levels are also important to follow, especially in those with recurrent calculi.

To identify those most likely to respond to dissolution therapy, Reichard et al. found that patients with 100% uric acid stones were older, heavier, and had a higher serum uric acid level, and lower urinary pH than those with mixed stones, while urinary uric acid was not significantly different among groups [30]. However, it is unclear whether these characteristics alone will provide enough specificity to predict uric acid stones.

Cystine stones

Cystinuria is an autosomal recessive disorder of dibasic amino acid transport in the kidney that leads to crystallization of poorly soluble cystine in the urine [51]. Between 3% and 59% of those who are homozygous for the trait will produce stones [52]. The disease is more severe in men than in women in terms of early appearance and number of produced stones. Although the incidence of cystine stones is only about 0.9%, cystine stones rank third in terms of rate of recurrence [53]. Treatment of cystine stones continues to be one of the most challenging therapeutic dilemmas in endourology because of a high frequency of recurrence, resistance to SWL, difficulty in localization, and the insufficient effect of oral chemolysis [44].

Because of the difficulties in treating cystine stones, much emphasis has been placed on prophylaxis. The solubility of cystine, like all amino acids, is pH‐dependent. Therefore, the production of alkaline urine can prevent cystine precipitation in the urine. A significant increase in cystine solubility begins to occur when urinary pH exceeds 7. For example, at a pH of 8, cystine solubility increases to approximately 1000 mg/l [54]. However, a significant drawback of urinary alkalinization is increased risk for calcium phosphate precipitation with pH above 7.5 [55]. For this reason, urinary pH of 7.5 is recommended [54]. It is recommended that this alkaline urinary pH must be maintained at night while the patient sleeps. The use of the potassium salts of citrate and bicarbonate may be more effective than the analogous sodium compounds because the presence of a sodium ion increases cystine excretion in the nephron. Because of this, a low‐sodium diet may be useful in the management of cystinuria [56].

Cystine is composed of two cysteine molecules joined by a disulfide bond and its dissolution requires alkalinization and splitting of the disulfide bond. This can be accomplished through either oral therapy or direct chemolytic therapy. D‐Penicillamine, the first oral agent used for cystine stones, is a disulfide exchange resin that facilitates separation at the disulfide bond through the thiol exchange reaction, forming mixed disulfides, and also decreases urinary excretion of cystine. The exchange reaction forms penicillamine disulfide–cysteine, which is 50 times more soluble than cystine [57] and is readily cleared through the urine. D‐Penicillamine is administered as 1–2 g in four divided doses, starting with a small dose and increasing as tolerated. Side‐effects of the drug include leukopenia, thrombocytopenia, gastrointestinal disturbances, skin rashes, proteinuria and nephrotic syndrome, neuropathies, and abnormalities of taste and smell. D‐Penicillamine has been reported to dissolve even large stones when combined with alkalinization but its potential side‐effects severely limit its usefulness.

α‐Mercaptopropionylglycine (MPG) is another disulfide exchange resin with fewer side‐effects than D‐penicillamine and appears to be more effective [58]. The usual dose of MPG is 600–1800 mg daily in four divided doses. Simultaneous treatment with oral sodium bicarbonate increases the effectiveness of this preparation because the disulfide exchange reaction is more active at higher pH levels.

Oral acetylcysteine, MPG, and D‐penicillamine are much more effective in preventing the formation of cystine calculi than dissolving them. When used for direct chemolysis, however, they are potent dissolution agents. During direct irrigation the solution bathing the stone will have a much higher concentration of the active agent. The pH of the solution is likewise more easily controlled, thereby facilitating the thiol exchange reaction [13].

Chemolysis monotherapy would require lengthy durations of irrigation for most stones. Approximately 9 days are required to dissolve a 1 cm cystine calculus. This irrigation time could be diminished when combined with SWL or percutaneous nephrolithotomy (PCNL), which reduce the stone burden and increase the surface area of the remaining fragments. Stones <1.5 cm may be treated initially with SWL since it increases the stone surface area and decreases dissolution time by nearly 50% [22]. If successful fragmentation occurs, repeat SWL or medical management may be sufficient as follow‐up therapy. Otherwise chemolysis alone or combined with PCNL is appropriate. For stones >1.5 cm, PCNL is the initial procedure of choice. Residual calculi, which are likely to remain, can be effectively treated with chemolysis and additional PCNL or SWL sessions. Simultaneous oral therapy should be implemented in all cases [13] (Table 29.1).

If the stones appear extremely resistant to therapeutic measures, the possibility of a mixed stone should not be overlooked. Hydroxyapatite, struvite, calcium oxalate, and calcium phosphate contaminants have been found to be present in 14–46% of cystine calculi analyzed in some studies [59].

In summary, although cystine urinary calculi continue to present a formidable challenge to urologists, successful eradication without open surgery may be accomplished with chemolytic techniques in conjunction with minimally invasive fragmentation procedures.

Struvite stones

Struvite stone formation typically occurs in patients with recurrent urinary tract infection and retained urine. Predisposing factors include urinary tract obstruction, chronic indwelling catheter, urinary diversion, and neurogenic voiding dysfunction [60]. Most commonly, staghorn stones are composed of a mixture of struvite (magnesium ammonium phosphate) and calcium carbonate apatite. In fact, hypercalciuric patients begin with calcium oxalate stone formation and develop superimposed infection with struvite deposition [61, 62]. Struvite calculi are typically referred to as “infection stones” because of their strong association with urinary tract infections caused by such bacteria. Silverman and Stamey [63] identified Proteus as the dominant microorganism in 72% of isolates from stone formers. Urease produced by such bacteria leads to hydrolysis of urea to ammonium, hydroxide, and bicarbonate, which increases the pH of the urine (pH >7.2). This alkaline urine, in the presence of trivalent phosphate, results in struvite crystal formation [64]. Other urease producers include Klebsiella, Pseudomonas, and Staphylococcus species [63, 65]. The most ubiquitous uropathogen, Escherichia coli, only rarely produces urease and thus is an infrequent cause of staghorn calculi [66].

Struvite stones are characterized by their large size and exceptionally rapid growth. It is not uncommon for a staghorn calculus to involve the entire renal pelvis and calices, nor for it to be formed within a four‐week period [60].

Management of struvite stone disease is one of the most frustrating problems in urology as efforts to eradicate such stones often have suboptimal success rates. The problem is not only ridding the patient of the calculi but also sterilizing the urine. Persistence of infection was estimated to occur in approximately 40% and is believed to be responsible for many of the stone recurrences [67]. The presence of small stone particles with embedded bacteria serves as a nidus for new stone formation and rapid recurrences. Therefore, postoperative irrigation therapy has been proposed to potentially reduce struvite stone recurrences [68, 69]. Medical dissolution therapy for struvite and carbonate apatite stones has been described as a second‐line treatment option. Oral chemolysis is available primarily in the form of urease inhibitors. Acetohydroxamic acid, the most commonly used agent, was identified as an irreversible urease inhibitor by Fishbein and Carbone [70]. The drug acts synergistically with several antibiotics, sterilizing the urine more rapidly, and its clinical usefulness has been demonstrated in double‐blind studies, although serious side‐effects precluded its use in patients even though they are reversible and dose‐related [71–73]. The usual dose is 250 mg orally three times daily to be reduced to twice daily for mild renal impairment, and it is contraindicated in patients with severe renal insufficiency and in pregnancy. Most common side‐effects reported were hemolytic anemia, neurosensory deficits, and thrombophlebitis. Headache, gastrointestinal upset, weakness, and flushing sensation after alcohol ingestion have also been reported [74]. Nevertheless, it is the only US Food and Drag Administration (FDA)‐approved urease inhibitor available today [75].

Systemic oral chemolytic agents are seldom effective in reducing stone burden on their own and direct chemolysis of struvite calculi is a far more effective method of dissolution. Suby and colleagues [76, 77] presented the first application of direct chemolysis to struvite calculi where the initial solution was found to be too irritant for urothelium to be clinically used. Suby’s solution G, formed by addition of magnesium to the previous formulation, has similar efficacy with decreased mucosal irritability (Table 29.2). Hemiacidrin (renacidin) is a multi‐electrolyte solution introduced by Mulvany [78] by modification of Suby’s solution. The acids present in this solution provide hydrogen ions and citrate to form soluble complexes with phosphate (phosphoric acid) and calcium (calcium citrate) from the stone (Table 29.3). Magnesium undergoes ion exchange with calcium present in the stone, enhancing dissolution while reducing irritation. The solubility of struvite is markedly increased at a pH <5.5, which occurs with each of the three variants of Suby’s solution. This finding was confirmed in a recent in vitro study by Jacobs et al. [79]. The success rate of these medications in the literature has been reported to occur in the range of 68–80% [80].

Infectious complications are known to occur as a result of dissolution therapy. Renacidin and Suby’s solutions have been implicated as the cause of urosepsis and death, and the FDA banned the use of renacidin irrigation for upper urinary tract stones on June 13, 1963 [90]. Urosepsis is thought to occur due to the release of large amounts of viable bacteria from stones as they dissolve. Therefore, it is critically important to stop treatment if fever occurs and until any infection has been adequately treated.

The presence of catheters and extensive use of antibiotics can also facilitate fungal infection. Replacing the irrigation fluid with amphotericin B (50 mg/500 ml H₂O) at a rate of 125 ml/h generally clears the funguria in less than 72 hours. Chemolysis irrigation can resume once urine cultures are negative for 24 hours.

Calcium stones

Calcium‐based calculi constitute about 80% of all urinary tract stone calculi of which about 80% are calcium oxalate stones [91], and yet they are the least amenable to chemolysis. The strong acids required to dissolve this compound cannot be safely used in humans. Only chelating agents have successfully been used in vivo to dissolve these types of stones. Ethylene‐diamine‐tetraacetic acid (EDTA) is the most commonly used solvent, and has shown moderate success in humans [92, 93] in spite of the significant urothelial injury reported [47]

Related posts:

1: Perioperative Considerations Radiation Safety During Diagnosis and Treatment Percutaneous Treatment of Ureteropelvic Junction Obstruction Management of Urolithiasis in Pregnancy Patient Preparation and Operating Room Setup for Laparoscopic and Robotic Surgery Pelvic Lymphadenectomy

Stay updated, free articles. Join our Telegram channel

Join