surgical options
In general, stones that are 4 mm in diameter or smaller will probably pass spontaneously, and stones that are larger than 8 mm are unlikely to pass without surgical intervention. With MET, stones 5-8 mm in size often pass, especially if located in the distal ureter. The larger the stone, the lower the possibility of spontaneous passage (and thus the greater the possibility that surgery will be required), although many other factors determine what happens with a particular stone.
Indications and contraindications
The primary indications for surgical treatment include pain, infection, and obstruction. Infection combined with urinary tract obstruction is an extremely dangerous situation, with significant risk of urosepsis and death, and must be treated emergently in virtually all cases. Additionally, certain occupational and health-related reasons exist.
General contraindications to definitive stone manipulation include the following:
Active, untreated UTI
Uncorrected bleeding diathesis
Pregnancy (a relative, but not absolute, contraindication)
Specific contraindications may apply to a given treatment modality. For example, do not perform SWL if a ureteral obstruction is distal to the calculus or in pregnancy.
Surgical options
For an obstructed and infected collecting system secondary to stone disease, virtually no contraindications exist for emergency surgical relief either by ureteral stent placement (a small tube placed endoscopically into the entire length of the ureter from the kidney to the bladder) or by percutaneous nephrostomy (a small tube placed through the skin of the flank directly into the kidney).
Many urologists have a preference for one technique or the other, but, in general, patients who are acutely ill, who have significant medical comorbidities, or who harbor stones that probably cannot be bypassed with ureteral stents undergo percutaneous nephrostomy, while others receive ureteral stent placement.
In patients who are floridly septic or hemodynamically unstable, a percutaneous nephrostomy is a faster and safer way to establish drainage of an infected and obstructed kidney. In these situations, retrograde approaches to drainage, if used at all, should be reserved for relatively mild cases in which patients are medically stable. Use appropriate urine cultures and antibiotics whenever a UTI is suspected in conjunction with hydronephrosis or renal colic.
The vast majority of symptomatic urinary tract calculi are now treated with noninvasive or minimally invasive techniques, while open surgical excision of a stone from the urinary tract is now limited to isolated atypical cases.
Guidelines are now available to assist the urologist in selecting surgical treatments. The 2005 American Urological Association (AUA) staghorn calculus guidelines recommend percutaneous nephrostolithotomy as the cornerstone of management.[55] In the ureteral stone guidelines produced by a joint effort of the AUA and the European Association of Urology, SWL and ureteroscopy are both recognized as first-line treatments for ureteral stones.[56]
Stent placement
Internal ureteral stents form a coil at either end when the stiffening insertion guide wire is removed. One coil forms in the renal pelvis and the other in the bladder. Stents are available in lengths from 20-30 cm and in 3 widths from 4.6F to 8.5F. Some are designed to soften after placement in the body; others are rather stiff to resist crushing and obstruction by large stones or external compression with occlusion from an extrinsic tumor or scar tissue.
To select the correct-size stent, estimates can be made based on the height of the patient, or the ureteral length can be measured. This is best performed by means of a retrograde pyelogram. The distance from the tip of the retrograde catheter to the UPJ is measured in centimeters with a tape measure. To account for the average magnification effect of the film, 10% of this reading is subtracted. If the result is an odd number, a double-J stent one size longer is used. The most common lengths used are 26 cm in men and 24 cm in women.
The optimal stent width depends on both the relative diameter and course of the ureter and the purpose of the stent. If the patient has a stricture or a tortuous ureter, a stiffer or larger-diameter stent is placed if possible.
When used for stone disease, stents perform several important functions. They virtually guarantee drainage of urine from the kidney into the bladder and bypass any obstruction. This relieves patients of their renal colic pain even if the actual stone remains. Over time, stents gently dilate the ureter, making ureteroscopy and other endoscopic surgical procedures easier to perform later.
Because they are also quite radiopaque, stents provide a stable landmark when performing SWL. A landmark is particularly important with small or barely visible stones, especially in the ureter, because the SWL machine uses radiographic visualization to target the stone.
Once large stones are broken up, stents tend to prevent the rapid dumping of large amounts of stone fragments and debris into the ureter (called steinstrasse). The stent forces the fragments to pass slowly, which is more efficient and prevents clogging.
Stents do have drawbacks. They can become blocked, kinked, dislodged, or infected. A KUB radiograph can be used to determine stent position, while infection is easily diagnosed by urinalysis. A renal sonogram can sometimes be helpful if there is concern for obstruction.
Questionable cases can be evaluated further using a radiographic cystogram or an IVP. The cystogram is performed by filling the urinary bladder with diluted contrast media through a Foley catheter under gravity pressure. A stent that is unclogged and functioning normally should show free reflux of contrast from the bladder into the stented renal pelvis.
The major drawback of stents, however, is that they are often quite uncomfortable for patients due to direct bladder irritation, spasm, and reflux. This discomfort can be alleviated to some extent by pain medications, anticholinergics (eg, oxybutynin, tolterodine), alpha-blockers, and topical analgesics (eg, phenazopyridine).
Percutaneous nephrostomy
In some cases, drainage of an obstructed kidney is necessary and stent placement is inadvisable or impossible. In particular, such cases include patients with pyonephrosis who have a UTI or urosepsis exacerbated by an obstructing calculus. In these patients, retrograde endourological procedures like retrograde pyelography and stent placement may exacerbate infection by pushing infected urinary material into the obstructed renal unit. Percutaneous nephrostomy is useful in such situations.[57]
Extracorporeal shockwave lithotripsy
SWL, the least invasive of the surgical methods of stone removal, utilizes an underwater energy wave focused on the stone to shatter it into passable fragments.
It is especially suitable for stones that are smaller than 2 cm and lodged in the upper or middle calyx. It is contraindicated in pregnancy, untreatable bleeding disorders, tightly impacted stones, or in cases of ureteral obstruction distal to the stone. In addition, the effectiveness is limited for very hard stones (which tend to be dense on CT scan), cystine stones, and in very large patients.
The patient, under varying degrees of anesthesia (depending on the type of lithotriptor used), is placed on a table or in a gantry that is then brought into contact with the shock head. The deeper the anesthesia (general endotracheal), the better the results. In addition, evidence is mounting that slower shockwave delivery (60-80 per min) improves the results. New lithotriptors that have 2 shock heads, which deliver a synchronous or asynchronous pair of shocks (possibly increasing efficacy), have attracted great interest.
The shock head delivers shockwaves developed from an electrohydraulic, electromagnetic, or piezoelectric source. The shockwaves are focused on the calculus, and the energy released as the shockwave impacts the stone produces fragmentation. The resulting small fragments pass in the urine.
SWL is limited somewhat by the size and location of the calculus. A stone larger than 1.5 cm in diameter or one located in the lower section of the kidney is treated less successfully. Fragmentation still occurs, but the large volume of fragments or their location in a dependent section of the kidney precludes complete passage. In addition, results may not be optimal in large patients, especially if the skin-to-stone distance exceeds 10 cm.[58]
Ureteroscopy
Along with SWL, ureteroscopic manipulation of a stone (see the image below) is a commonly applied method of stone removal. A small endoscope, which may be rigid, semirigid, or flexible, is passed into the bladder and up the ureter to directly visualize the stone.
Two calculi in a dependent calyx of the kidney (lower pole) visualized through a flexible fiberoptic ureteroscope. In another location, these calculi might have been treated with extracorporeal shockwave lithotripsy (ESWL), but, after being counseled regarding the lower success rate of ESWL for stones in a dependent location, the patient elected ureteroscopy. Note that the image provided by fiberoptics, although still acceptable, is inferior to that provided by the rod-lens optics of the rigid ureteroscope in the previous picture.
Ureteroscopy is especially suitable for removal of stones that are 1-2 cm, lodged in the lower calyx or below, cystine stones, and high attenuation ("hard") stones. The typical patient has acute symptoms caused by a distal ureteral stone, usually measuring 5-8 mm. Stones smaller than 5 mm in diameter generally are retrieved using a stone basket, whereas tightly impacted stones or those larger than 5 mm are manipulated proximally for SWL or are fragmented using an endoscopic direct-contact fragmentation device.
Often, a ureteral stent must be placed after ureteroscopy in order to prevent obstruction from ureteral spasm and edema. Since a ureteral stent is often uncomfortable, many urologists eschew stent placement following ureteroscopy in selected patients.[59]
Percutaneous nephrostolithotomy
Percutaneous nephrostolithotomy allows fragmentation and removal of large calculi from the kidney and ureter. Because of their increased morbidity compared with SWL and ureteroscopy, percutaneous procedures are generally reserved for large and/or complex renal stones and failures from the other 2 modalities. Percutaneous nephrostolithotomy is especially useful for stones larger than 2 cm in diameter.
A needle and then a wire, over which is passed a hollow sheath, are inserted directly into the kidney through the skin of the flank. Percutaneous access to the kidney typically involves a sheath with a 1-cm lumen, which will admit relatively large endoscopes with powerful and effective lithotrites that can rapidly fragment and remove large stone volumes. Renal calyces, pelvis, and proximal ureter can be examined and stones extracted with or without prior fragmentation.
In some cases, a combination of SWL and a percutaneous technique is necessary to completely remove all stone material from a kidney. This technique, called sandwich therapy, is reserved for staghorn or other complicated stone cases. In such cases, experience has shown that the final procedure should be percutaneous nephrostolithotomy.
Open nephrostomy
Open nephrostomy has been used less and less often since the development of SWL and endoscopic and percutaneous techniques; it now constitutes less than 1% of all interventions. Disadvantages include longer hospitalization, longer convalescence, and increased requirements for blood transfusion.
medical therapy for stone disease
Dissolution of calculi
Urinary calculi composed predominantly of calcium cannot be dissolved with current medical therapy; however, medical therapy is important in the long-term chemoprophylaxis of further calculus growth or formation.
Uric acid and cystine calculi can be dissolved with medical therapy. Patients with uric acid stones who do not require urgent surgical intervention for reasons of pain, obstruction, or infection can often have their stones dissolved with alkalization of the urine. Sodium bicarbonate can be used as the alkalizing agent, but potassium citrate is usually preferred because of the availability of slow-release tablets and the avoidance of a high sodium load.
The dosage of the alkalizing agent should be adjusted to maintain the urinary pH between 6.5 and 7.0. Urinary pH of more than 7.5 should be avoided because of the potential deposition of calcium phosphate around the uric acid calculus, which would make it undissolvable. Both uric acid and cystine calculi form in acidic environments.
Even very large uric acid calculi can be dissolved in patients who comply with therapy. Roughly 1 cm per month dissolution can be achieved. Practical ability to alkalinize the urine significantly limits the ability to dissolve cystine calculi.
Chemoprophylaxis
Prophylactic therapy might include limitation of dietary components, addition of stone-formation inhibitors or intestinal calcium binders, and, most importantly, augmentation of fluid intake. (See Dietary Measures and Prevention of Nephrolithiasis.) Besides advising patients to avoid excessive salt and protein intake and to increase fluid intake, base medical therapy for long-term chemoprophylaxis of urinary calculi on the results of a 24-hour urinalysis for chemical constituents.
Chemoprophylaxis of uric acid and cystine calculi consists primarily of long-term alkalinization of urine. If hyperuricosuria or hyperuricemia is documented in patients with pure uric acid stones (present in only a relative minority), allopurinol (300 mg qd) is recommended because it reduces uric acid excretion.
Pharmaceuticals that can bind free cystine in the urine (eg, D-penicillamine, 2-alpha-mercaptopropionyl-glycine) help reduce stone formation in cystinuria. Therapy should also include long-term urinary alkalinization and aggressive fluid intake. Captopril has been shown to be effective in some trials, although, again, strong data are lacking. Routine use should be avoided but can be added in patients who have difficulty in dissolving and preventing cystine stones.
In almost all patients in whom stones form, an increase in fluid intake and, therefore, an increase in urine output is recommended. This is likely the single most important aspect of stone prophylaxis. Patients with recurrent nephrolithiasis traditionally have been instructed to drink 8 glasses of fluid daily to maintain adequate hydration and decrease chance of urinary supersaturation with stone-forming salts. The goal is a total urine volume in 24 hours in excess of 2 liters.
The only other general dietary guidelines are to avoid excessive salt and protein intake. Moderation of calcium and oxalate intake is also reasonable, but great care must be taken not to indiscriminately instruct the patient to reduce calcium intake.
Dietary calcium should not be restricted beyond normal unless specifically indicated based on 24-hour urinalysis findings. Urinary calcium levels are normal in many patients with calcium stones. Reducing dietary calcium in these patients may actually worsen their stone disease, because more oxalate is absorbed from the GI tract in the absence of sufficient intestinal calcium to bind with it. This results in a net increase in oxalate absorption and hyperoxaluria, which tends to increase new kidney stone formation in patients with calcium oxalate calculi.
An empiric restriction of dietary calcium may also adversely affect bone mineralization and may have osteoporosis implications, especially in women. This practice should be condemned unless indicated based on a metabolic evaluation.
As a rule, dietary calcium should be restricted to 600-800 mg/d in patients with diet-responsive hypercalciuria who form calcium stones. This is roughly equivalent to a single high-calcium or dairy meal per day.
prevention of nephrolithiasis
The most common causes of kidney stones are hypercalciuria, hyperuricosuria, hyperoxaluria, hypocitraturia, and low urinary volume. Each of these major factors can be measured easily with a 24-hour urine sample using one of several commercial laboratory packages now available. Kidney stone preventive therapy consists of dietary adjustments, nutritional supplements, medications, or combinations of these.
Strongly encourage patients who have a stone at a young age (ie, < 25 y), multiple recurrences, a solitary functioning kidney, or a history of prior kidney stone surgery to obtain a 24-hour urine collection for stone prevention analysis, especially if they are motivated to comply with a long-term stone prevention program. These 24-hour urine collection kits can be obtained from a number of commercial medical laboratories.
consultations
Consultation with a urologist is required when immediate ED management of renal (ureteral) colic fails. Referral to a urologist is necessary for all stones that prove refractory to outpatient management or that fail to pass spontaneously.
Consult a urologist immediately in cases of ureterolithiasis with proximal UTI. Infected hydronephrosis is a true urologic emergency and requires hospital admission, IV fluids, IV antibiotics, and immediate drainage of the infected hydronephrosis via percutaneous nephrostomy or ureteral stent placement.
Urologic consultation is also appropriate in patients with unusually large stones, high-risk medical conditions, inability to tolerate oral fluids and medications, unrelenting pain, renal failure, renal transplant, a solitary functioning kidney, or a history of prior stones that required invasive intervention.
Patients who are pregnant require a consultation with an obstetrician-gynecologist, and those with a history of severe cardiac disease or congestive heart failure may benefit from involvement of an internal medicine specialist or cardiologist.
Patients with strong motivation to prevent all future stones, those with multiple recurrences or single functioning kidneys, and all children younger than 16 years with nephrolithiasis should be referred to a specialist in nephrolithiasis prevention. A medical expert in metabolic stone prevention testing, interpretation, and prophylactic therapy is available in most communities.
In general, stones that are 4 mm in diameter or smaller will probably pass spontaneously, and stones that are larger than 8 mm are unlikely to pass without surgical intervention. With MET, stones 5-8 mm in size often pass, especially if located in the distal ureter. The larger the stone, the lower the possibility of spontaneous passage (and thus the greater the possibility that surgery will be required), although many other factors determine what happens with a particular stone.
Indications and contraindications
The primary indications for surgical treatment include pain, infection, and obstruction. Infection combined with urinary tract obstruction is an extremely dangerous situation, with significant risk of urosepsis and death, and must be treated emergently in virtually all cases. Additionally, certain occupational and health-related reasons exist.
General contraindications to definitive stone manipulation include the following:
Active, untreated UTI
Uncorrected bleeding diathesis
Pregnancy (a relative, but not absolute, contraindication)
Specific contraindications may apply to a given treatment modality. For example, do not perform SWL if a ureteral obstruction is distal to the calculus or in pregnancy.
Surgical options
For an obstructed and infected collecting system secondary to stone disease, virtually no contraindications exist for emergency surgical relief either by ureteral stent placement (a small tube placed endoscopically into the entire length of the ureter from the kidney to the bladder) or by percutaneous nephrostomy (a small tube placed through the skin of the flank directly into the kidney).
Many urologists have a preference for one technique or the other, but, in general, patients who are acutely ill, who have significant medical comorbidities, or who harbor stones that probably cannot be bypassed with ureteral stents undergo percutaneous nephrostomy, while others receive ureteral stent placement.
In patients who are floridly septic or hemodynamically unstable, a percutaneous nephrostomy is a faster and safer way to establish drainage of an infected and obstructed kidney. In these situations, retrograde approaches to drainage, if used at all, should be reserved for relatively mild cases in which patients are medically stable. Use appropriate urine cultures and antibiotics whenever a UTI is suspected in conjunction with hydronephrosis or renal colic.
The vast majority of symptomatic urinary tract calculi are now treated with noninvasive or minimally invasive techniques, while open surgical excision of a stone from the urinary tract is now limited to isolated atypical cases.
Guidelines are now available to assist the urologist in selecting surgical treatments. The 2005 American Urological Association (AUA) staghorn calculus guidelines recommend percutaneous nephrostolithotomy as the cornerstone of management.[55] In the ureteral stone guidelines produced by a joint effort of the AUA and the European Association of Urology, SWL and ureteroscopy are both recognized as first-line treatments for ureteral stones.[56]
Stent placement
Internal ureteral stents form a coil at either end when the stiffening insertion guide wire is removed. One coil forms in the renal pelvis and the other in the bladder. Stents are available in lengths from 20-30 cm and in 3 widths from 4.6F to 8.5F. Some are designed to soften after placement in the body; others are rather stiff to resist crushing and obstruction by large stones or external compression with occlusion from an extrinsic tumor or scar tissue.
To select the correct-size stent, estimates can be made based on the height of the patient, or the ureteral length can be measured. This is best performed by means of a retrograde pyelogram. The distance from the tip of the retrograde catheter to the UPJ is measured in centimeters with a tape measure. To account for the average magnification effect of the film, 10% of this reading is subtracted. If the result is an odd number, a double-J stent one size longer is used. The most common lengths used are 26 cm in men and 24 cm in women.
The optimal stent width depends on both the relative diameter and course of the ureter and the purpose of the stent. If the patient has a stricture or a tortuous ureter, a stiffer or larger-diameter stent is placed if possible.
When used for stone disease, stents perform several important functions. They virtually guarantee drainage of urine from the kidney into the bladder and bypass any obstruction. This relieves patients of their renal colic pain even if the actual stone remains. Over time, stents gently dilate the ureter, making ureteroscopy and other endoscopic surgical procedures easier to perform later.
Because they are also quite radiopaque, stents provide a stable landmark when performing SWL. A landmark is particularly important with small or barely visible stones, especially in the ureter, because the SWL machine uses radiographic visualization to target the stone.
Once large stones are broken up, stents tend to prevent the rapid dumping of large amounts of stone fragments and debris into the ureter (called steinstrasse). The stent forces the fragments to pass slowly, which is more efficient and prevents clogging.
Stents do have drawbacks. They can become blocked, kinked, dislodged, or infected. A KUB radiograph can be used to determine stent position, while infection is easily diagnosed by urinalysis. A renal sonogram can sometimes be helpful if there is concern for obstruction.
Questionable cases can be evaluated further using a radiographic cystogram or an IVP. The cystogram is performed by filling the urinary bladder with diluted contrast media through a Foley catheter under gravity pressure. A stent that is unclogged and functioning normally should show free reflux of contrast from the bladder into the stented renal pelvis.
The major drawback of stents, however, is that they are often quite uncomfortable for patients due to direct bladder irritation, spasm, and reflux. This discomfort can be alleviated to some extent by pain medications, anticholinergics (eg, oxybutynin, tolterodine), alpha-blockers, and topical analgesics (eg, phenazopyridine).
Percutaneous nephrostomy
In some cases, drainage of an obstructed kidney is necessary and stent placement is inadvisable or impossible. In particular, such cases include patients with pyonephrosis who have a UTI or urosepsis exacerbated by an obstructing calculus. In these patients, retrograde endourological procedures like retrograde pyelography and stent placement may exacerbate infection by pushing infected urinary material into the obstructed renal unit. Percutaneous nephrostomy is useful in such situations.[57]
Extracorporeal shockwave lithotripsy
SWL, the least invasive of the surgical methods of stone removal, utilizes an underwater energy wave focused on the stone to shatter it into passable fragments.
It is especially suitable for stones that are smaller than 2 cm and lodged in the upper or middle calyx. It is contraindicated in pregnancy, untreatable bleeding disorders, tightly impacted stones, or in cases of ureteral obstruction distal to the stone. In addition, the effectiveness is limited for very hard stones (which tend to be dense on CT scan), cystine stones, and in very large patients.
The patient, under varying degrees of anesthesia (depending on the type of lithotriptor used), is placed on a table or in a gantry that is then brought into contact with the shock head. The deeper the anesthesia (general endotracheal), the better the results. In addition, evidence is mounting that slower shockwave delivery (60-80 per min) improves the results. New lithotriptors that have 2 shock heads, which deliver a synchronous or asynchronous pair of shocks (possibly increasing efficacy), have attracted great interest.
The shock head delivers shockwaves developed from an electrohydraulic, electromagnetic, or piezoelectric source. The shockwaves are focused on the calculus, and the energy released as the shockwave impacts the stone produces fragmentation. The resulting small fragments pass in the urine.
SWL is limited somewhat by the size and location of the calculus. A stone larger than 1.5 cm in diameter or one located in the lower section of the kidney is treated less successfully. Fragmentation still occurs, but the large volume of fragments or their location in a dependent section of the kidney precludes complete passage. In addition, results may not be optimal in large patients, especially if the skin-to-stone distance exceeds 10 cm.[58]
Ureteroscopy
Along with SWL, ureteroscopic manipulation of a stone (see the image below) is a commonly applied method of stone removal. A small endoscope, which may be rigid, semirigid, or flexible, is passed into the bladder and up the ureter to directly visualize the stone.
Two calculi in a dependent calyx of the kidney (lower pole) visualized through a flexible fiberoptic ureteroscope. In another location, these calculi might have been treated with extracorporeal shockwave lithotripsy (ESWL), but, after being counseled regarding the lower success rate of ESWL for stones in a dependent location, the patient elected ureteroscopy. Note that the image provided by fiberoptics, although still acceptable, is inferior to that provided by the rod-lens optics of the rigid ureteroscope in the previous picture.
Ureteroscopy is especially suitable for removal of stones that are 1-2 cm, lodged in the lower calyx or below, cystine stones, and high attenuation ("hard") stones. The typical patient has acute symptoms caused by a distal ureteral stone, usually measuring 5-8 mm. Stones smaller than 5 mm in diameter generally are retrieved using a stone basket, whereas tightly impacted stones or those larger than 5 mm are manipulated proximally for SWL or are fragmented using an endoscopic direct-contact fragmentation device.
Often, a ureteral stent must be placed after ureteroscopy in order to prevent obstruction from ureteral spasm and edema. Since a ureteral stent is often uncomfortable, many urologists eschew stent placement following ureteroscopy in selected patients.[59]
Percutaneous nephrostolithotomy
Percutaneous nephrostolithotomy allows fragmentation and removal of large calculi from the kidney and ureter. Because of their increased morbidity compared with SWL and ureteroscopy, percutaneous procedures are generally reserved for large and/or complex renal stones and failures from the other 2 modalities. Percutaneous nephrostolithotomy is especially useful for stones larger than 2 cm in diameter.
A needle and then a wire, over which is passed a hollow sheath, are inserted directly into the kidney through the skin of the flank. Percutaneous access to the kidney typically involves a sheath with a 1-cm lumen, which will admit relatively large endoscopes with powerful and effective lithotrites that can rapidly fragment and remove large stone volumes. Renal calyces, pelvis, and proximal ureter can be examined and stones extracted with or without prior fragmentation.
In some cases, a combination of SWL and a percutaneous technique is necessary to completely remove all stone material from a kidney. This technique, called sandwich therapy, is reserved for staghorn or other complicated stone cases. In such cases, experience has shown that the final procedure should be percutaneous nephrostolithotomy.
Open nephrostomy
Open nephrostomy has been used less and less often since the development of SWL and endoscopic and percutaneous techniques; it now constitutes less than 1% of all interventions. Disadvantages include longer hospitalization, longer convalescence, and increased requirements for blood transfusion.
medical therapy for stone disease
Dissolution of calculi
Urinary calculi composed predominantly of calcium cannot be dissolved with current medical therapy; however, medical therapy is important in the long-term chemoprophylaxis of further calculus growth or formation.
Uric acid and cystine calculi can be dissolved with medical therapy. Patients with uric acid stones who do not require urgent surgical intervention for reasons of pain, obstruction, or infection can often have their stones dissolved with alkalization of the urine. Sodium bicarbonate can be used as the alkalizing agent, but potassium citrate is usually preferred because of the availability of slow-release tablets and the avoidance of a high sodium load.
The dosage of the alkalizing agent should be adjusted to maintain the urinary pH between 6.5 and 7.0. Urinary pH of more than 7.5 should be avoided because of the potential deposition of calcium phosphate around the uric acid calculus, which would make it undissolvable. Both uric acid and cystine calculi form in acidic environments.
Even very large uric acid calculi can be dissolved in patients who comply with therapy. Roughly 1 cm per month dissolution can be achieved. Practical ability to alkalinize the urine significantly limits the ability to dissolve cystine calculi.
Chemoprophylaxis
Prophylactic therapy might include limitation of dietary components, addition of stone-formation inhibitors or intestinal calcium binders, and, most importantly, augmentation of fluid intake. (See Dietary Measures and Prevention of Nephrolithiasis.) Besides advising patients to avoid excessive salt and protein intake and to increase fluid intake, base medical therapy for long-term chemoprophylaxis of urinary calculi on the results of a 24-hour urinalysis for chemical constituents.
Chemoprophylaxis of uric acid and cystine calculi consists primarily of long-term alkalinization of urine. If hyperuricosuria or hyperuricemia is documented in patients with pure uric acid stones (present in only a relative minority), allopurinol (300 mg qd) is recommended because it reduces uric acid excretion.
Pharmaceuticals that can bind free cystine in the urine (eg, D-penicillamine, 2-alpha-mercaptopropionyl-glycine) help reduce stone formation in cystinuria. Therapy should also include long-term urinary alkalinization and aggressive fluid intake. Captopril has been shown to be effective in some trials, although, again, strong data are lacking. Routine use should be avoided but can be added in patients who have difficulty in dissolving and preventing cystine stones.
In almost all patients in whom stones form, an increase in fluid intake and, therefore, an increase in urine output is recommended. This is likely the single most important aspect of stone prophylaxis. Patients with recurrent nephrolithiasis traditionally have been instructed to drink 8 glasses of fluid daily to maintain adequate hydration and decrease chance of urinary supersaturation with stone-forming salts. The goal is a total urine volume in 24 hours in excess of 2 liters.
The only other general dietary guidelines are to avoid excessive salt and protein intake. Moderation of calcium and oxalate intake is also reasonable, but great care must be taken not to indiscriminately instruct the patient to reduce calcium intake.
Dietary calcium should not be restricted beyond normal unless specifically indicated based on 24-hour urinalysis findings. Urinary calcium levels are normal in many patients with calcium stones. Reducing dietary calcium in these patients may actually worsen their stone disease, because more oxalate is absorbed from the GI tract in the absence of sufficient intestinal calcium to bind with it. This results in a net increase in oxalate absorption and hyperoxaluria, which tends to increase new kidney stone formation in patients with calcium oxalate calculi.
An empiric restriction of dietary calcium may also adversely affect bone mineralization and may have osteoporosis implications, especially in women. This practice should be condemned unless indicated based on a metabolic evaluation.
As a rule, dietary calcium should be restricted to 600-800 mg/d in patients with diet-responsive hypercalciuria who form calcium stones. This is roughly equivalent to a single high-calcium or dairy meal per day.
prevention of nephrolithiasis
The most common causes of kidney stones are hypercalciuria, hyperuricosuria, hyperoxaluria, hypocitraturia, and low urinary volume. Each of these major factors can be measured easily with a 24-hour urine sample using one of several commercial laboratory packages now available. Kidney stone preventive therapy consists of dietary adjustments, nutritional supplements, medications, or combinations of these.
Strongly encourage patients who have a stone at a young age (ie, < 25 y), multiple recurrences, a solitary functioning kidney, or a history of prior kidney stone surgery to obtain a 24-hour urine collection for stone prevention analysis, especially if they are motivated to comply with a long-term stone prevention program. These 24-hour urine collection kits can be obtained from a number of commercial medical laboratories.
consultations
Consultation with a urologist is required when immediate ED management of renal (ureteral) colic fails. Referral to a urologist is necessary for all stones that prove refractory to outpatient management or that fail to pass spontaneously.
Consult a urologist immediately in cases of ureterolithiasis with proximal UTI. Infected hydronephrosis is a true urologic emergency and requires hospital admission, IV fluids, IV antibiotics, and immediate drainage of the infected hydronephrosis via percutaneous nephrostomy or ureteral stent placement.
Urologic consultation is also appropriate in patients with unusually large stones, high-risk medical conditions, inability to tolerate oral fluids and medications, unrelenting pain, renal failure, renal transplant, a solitary functioning kidney, or a history of prior stones that required invasive intervention.
Patients who are pregnant require a consultation with an obstetrician-gynecologist, and those with a history of severe cardiac disease or congestive heart failure may benefit from involvement of an internal medicine specialist or cardiologist.
Patients with strong motivation to prevent all future stones, those with multiple recurrences or single functioning kidneys, and all children younger than 16 years with nephrolithiasis should be referred to a specialist in nephrolithiasis prevention. A medical expert in metabolic stone prevention testing, interpretation, and prophylactic therapy is available in most communities.
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