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How to avoid kidney stones.

Dietary Modifications

It is now firmly established that alterations in the handling of calcium by the body are responsible for a large percentage (over 65 percent) of kidney stones. The changes in calcium metabolism are frequently accompanied by abnormalities in the metabolism of two compounds that are products of the chemical reactions that constantly keep us going: oxalate and uric acid. Thus, it is not surprising that attempts at curbing the incidence of stones or "stone episodes" (e.g., colic, stone passage, etc.) include control of the metabolism of calcium, oxalate, and uric acid. While all these compounds are part of the normal composition of our bodies, we also ingest them in our food, which may modify their handling by the body and contribute to stone formation.

Calcium and Dairy Products

Dairy products are, of course, rich in calcium, and their ingestion may compound the presence of too much calcium in the urine (hypercalciuria). Calcium in the diet is absorbed in the intestine and excreted in the urine. High levels of calcium in the urine predispose to stone formation. Moreover, if the volume of urine is relatively low, the concentration of the excess calcium will be higher than it ought to be and propitiate the formation of stones.

It is therefore recommended that all patients who have stones should take two important measures in an attempt to reduce the incidence of stones and prevent their further formation: limit dairy product consumption and ingest enough fluids to keep urine output greater than two liters per day. Patients must themselves be willing to undertake these two simple, and inexpensive, maneuvers.

Uric Acid and Purine Sources

Uric acid has been found to worsen the incidence of calcium stone episodes in as many as 30 percent of patients with calcium stones. Uric acid is the end-product of the breakdown of a group of compounds called purines. These in turn have their precursors in the components of the cell nucleus. Most animal cells have a nucleus, and meat, poultry and fish are rich in cells that have nuclei and thus are sources of purines and, ultimately, of uric acid.

Avoiding "Purine Gluttony"

There are individuals who eat these foods at the exclusion of some that have fewer purines, such as bread, grain, and starches. This has been called "purine gluttony" and may be enormously deleterious to stone formation. Therefore, reduction in the consumption of animal protein, particularly if it has been determined that urine uric acid excretion is higher than normal, may be a crucial step in preventing stone formation.

Oxalate production is much more an endogenous process, and close to 90 percent of its concentration in the urine comes from the activity of the liver. The rest can be traced to food we eat either directly as oxalate and/or ascorbic acid. Overproduction of oxalate by the liver and excess intake of oxalate-rich foods (rhubarb, spinach, parsley, cocoa, etc.), may contribute to high levels of oxalate in urine and increase the incidence of stones. Under most circumstances, however, dietary indiscretion is not as prominent a contributor to excess oxalate in the urine as is true with purines.

On the other hand, a series of gastrointestinal disturbances such as inflammatory bowel disease, small bowel resection, or jejunoileal bypass (connection of the duodenum to the colon) may set up the patient for hyperabsorption of oxalate from dietary sources and increase the incidence of stones. In addition, the bowel disease may lead to loss of fluids and low urine volumes which will also compound the susceptibility for stone formation. Special care by the physician is almost invariably required in these individuals, who may also benefit from dietary modification.

It should be clear that preventive measures must be carefully planned and instituted after consultation with the physician and the proper diagnostic workup has been performed.

Other Stones, Other Foods

A particularly problematic type of stone is that associated with infection. Almost always, these are formed when infections with urea-splitting (urea is the end-product of the metabolism of protein) organisms are present. These bugs take urea and transform it into ammonia, which forms a complex with magnesium and phosphate to become something called struvite (or magnesium-ammonium-phosphate), which is the most important component of "infectious" stones. It is not easy to cure these, and they grow to form large "staghorn" calculi (stones) that get trapped in the pelvis of the kidney and cause a lot of problems.

Antibiotics are not very effective under these circumstances, particularly because the bugs can live in the crevices of the stones where the medication cannot get to. A medication called acetohydroxamic acid (AHA), which is a urease inhibitor, may reduce the concentration of struvite in the urine and slow the formation of stones, but it may produce too many side effects if used chronically. For these reasons, in the immediate past, struvite stones have been removed surgically while they are now treated with a combination of percutaneous ultrasound debulking and extracorporeal shock wave lithotripsy (see below).

Needless to say, it would be best to avoid the development of urinary tract infections. Recently, it has been determined that regular intake of cranberry juice reduced the odds of developing bacteriuria (bacteria in the urine) in elderly women (mean age 78.5 years). Another study suggested that not only bacteriuria, but the presence of pus cells in the urine (pyuria) was reduced by nearly 50 percent in elderly women who drank 300 milliliters (equivalent to 10 ounces) of cranberry juice each day for six months. Cranberry juice has also been shown to inhibit bacteria from attaching to the epithelial cells (those that coat) of the urinary tract.

Despite these promising observations, the efficacy of cranberry juice must be established more definitively by further studies. It should be clear that the use of cranberry juice in stone formers has not been the subject of prospective, rigorous scientific analysis. Therefore, whether it plays a role in stone prevention is presently unknown.

Extracorporeal Shock Wave Lithotripsy (ESWL)

Since the development of ESWL by the University of Munich-Dornier Aerospace Engineering Company, the treatment of stone disease has been revolutionized. While the original model is still in use, there are now "second-generation" lithotripters that offer some technological advances, one of which is that the patient need not be immersed in water.

Nowadays, fluid-filled cushions can be used to achieve the same shock-wave transmission as afforded by water tubs. Ultrasonic lithotripsy can be given through percutaneous or ureteroscopic means. This helps reduce the bulk ("debulking" the stone) of the calculus, making it easier for ESWL to shatter its remains.

As I mentioned previously, this is today the management of choice for the staghorn calculi associated with infections, and while the combination of percutaneous ultrasound and ESWL requires time (several days) in the hospital, the recovery is good and certainly shorter than standard operative intervention. Moreover, follow-up experience suggests that the treatment is efficient and successful.

The most common complications associated with ESWL are loss of renal function and development of hypertension. Both are extremely low with the new technology, which makes ESWL the safest intervention for the management of stones. Morbidity and mortality of morbidly obese patients (patients weighing more than 50 percent of their predicted weight) can be increased since the stone is at considerable distance from the skin and positioning of the patient may be problematic.

Yet, recent studies using second-generation lithotripters have been done, and the results achieved have been comparable to those attained in non-obese patients. Damage of the kidney as a result of ESWL or percutaneous ultrasound lithotripsy, or from complications of the presence of a stone that has led to obstruction and its attendant effects on the structure of the kidney, may lead to a nephrectomy.

Nephrectomy (Kidney Removal)

Persons who have donated a kidney to a relative are by far the group of patients most studied in relation to what happens to the remaining kidney. For the most part, what does happen is that the kidney grows larger and can take up to 85 to 90 percent of the function previously carried out by two kidneys. This is no different in patients who have lost a kidney to accidents, unilateral kidney disease, etc. In the case of patients who have lost one kidney to stone disease, the future may be clouded if the remaining kidney were to be afflicted with stone disease as well.

Controversy has surrounded the longterm effects of nephrectomy on renal function in the remaining organ. The most critical issue has concerned the development of high blood flow to the remaining kidney, which is known to result in some renal damage in experimental animals. The changes in the remaining kidney have been studied extensively and potentially include hypertension, reduced kidney function, and pathological proteinuria. Nevertheless, few adverse effects have been seen and longterm ill-effects of nephrectomy have been few and and minor.

No evidence has been found that, in the aggregate, nephrectomy reduces survival. Clearly, frequent consultation with the physician and adherence to therapy and preventive measures will most likely avoid the possibility of nephrectomy, which should be a treatment of last resort.
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Title Annotation:dietary aids may help prevent stone formation and lithotripsy may destroy them if they do form
Author:Martinez-Maldonado, Manuel
Publication:Saturday Evening Post
Date:Sep 1, 1995
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Next Article:Unsung hero of lithotripsy.

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