What is the treatment for kidney stones?
Most kidney stones eventually pass through the
urinary tract on their own within 48 hours, with ample fluid intake. Pain
medications are used for symptom relief. When over-the-counter medications are
not sufficient for pain control, narcotics may be prescribed. Intravenous pain
medications can be given when nausea and vomiting are present.
There are several factors which influence the ability to pass a stone. These
include the size of the person, prior stone passage, prostate enlargement,
pregnancy, and the size of the stone. A 4 mm stone has an 80% chance of passage
while a 5 mm stone has a 20% chance. Stones larger than 9 mm-10 mm rarely pass
without specific treatment.
Some medications have been used to increase the passage rates of kidney stones.
These include calcium channel blockers such as nifedipine (Adalat, Procardia,
Afeditab, Nifediac) and alpha blockers such as tamsulosin (Flomax). These drugs
may be prescribed to some people who have stones that do not rapidly pass
through the urinary tract.
For kidney stones that do not pass on their own, a procedure called lithotripsy
is often used. In this procedure, shock waves are used to break up a large
stone into smaller pieces that can then pass through the urinary system.
Surgical techniques have also been developed to remove kidney stones when other
treatment methods are not effective. This may be done through a small incision
in the skin (percutaneous nephrolithotomy) or through an instrument known as an
ureteroscope passed through the urethra and bladder up into the ureter.
Classification
Kidney stones are typically classified by their location and chemical
composition.
|
Kidney Stone
type
|
Population
|
Circumstances
|
Details
|
|
Calcium oxalate
|
80%
|
when urine is acidic (low pH)
|
Some of the oxalate in urine is produced by the body.
Calcium and oxalate in the diet play a part but are not the only factors that
affect the formation of calcium oxalate stones. Dietary oxalate is an organic
molecule found in many vegetables, fruits, and nuts. Calcium from bone may
also play a role in kidney stone formation.
|
|
Calcium phosphate
|
___%
|
when urine is alkaline (high pH)
|
|
|
Uric acid
|
5-10%
|
when urine is persistently acidic
|
Diets rich in animal proteins and purines: substances
found naturally in all food but especially in organ meats, fish, and
shellfish.
|
|
Struvite
|
10-15%
|
infections in the kidney
|
Preventing struvite stones depends on staying
infection-free. Diet has not been shown to affect struvite stone formation.
|
|
Cystine
|
___%
|
rare genetic disorder
|
Cystine, an amino acid (one of the building blocks of
protein), leaks through the kidneys and into the urine to form crystals.
|
Prevention
Dietary measures
Specific therapy should be tailored to the type of stones involved. Diet can
have a profound influence on the development of kidney stones. Preventive
strategies include some combination of dietary modifications and medications
with the goal of reducing the excretory load of calculogenic compounds on the
kidneys. Current dietary recommendations to minimize the formation of kidney
stones include:
- Increasing fluid intake of citrate-rich
foods (especially citrate-rich fluids such as lemonade
and orange juice), with the objective of increasing urine output to
more than two liters per day
- Attempt to maintain a calcium (Ca)
intake of 1000 – 1200 mg per day
- Limiting sodium (Na)
intake to less than 2300 mg per day
- Limiting vitamin C
intake to less than 1000 mg per day
- Limiting animal protein
intake to no more than two meals daily, with less than 170–230
g per day. (A positive association between animal protein consumption and recurrence of
kidney stones has been shown in men.
- Limiting consumption of foods
containing high amounts of oxalate (such as spinach, strawberries, nuts,
rhubarb, wheat
germ, dark chocolate, cocoa,
brewed tea)
Maintenance of dilute urine by means of vigorous fluid therapy is beneficial
in all forms of nephrolithiasis, so increasing urine volume is a key principle
for the prevention of kidney stones. Fluid intake should be sufficient to
maintain a urine output of at least 2 l (68 US fl oz)
per day.A high fluid intake has been associated with a 40% reduction in
recurrence risk.
Calcium binds with available oxalate in the gastrointestinal tract, thereby
preventing its absorption into the bloodstream, and reducing oxalate absorption
decreases kidney stone risk in susceptible people. Because of this, some
nephrologists
and
urologists
recommend chewing calcium tablets during meals containing oxalate foods.
Calcium citrate supplements can be taken with meals if dietary calcium cannot
be increased by other means. The preferred calcium supplement for people at
risk of stone formation is calcium citrate because it helps to increase urinary
citrate excretion.
Aside from vigorous oral hydration and consumption of more dietary calcium,
other prevention strategies include avoidance of large doses of supplemental
vitamin C and restriction of oxalate-rich foods such as
leaf vegetables,
rhubarb,
soy products and
chocolate.
However, no randomized, controlled trial of oxalate restriction has yet been
performed to test the hypothesis that oxalate restriction reduces the incidence
of stone formation. Some evidence indicates
magnesium
intake decreases the risk of symptomatic nephrolithiasis.
Urine alkalinization
The mainstay for medical management of uric acid stones is alkalinization
(increasing the pH) of the urine. Uric acid stones are among the few types
amenable to dissolution therapy, referred to as chemolysis. Chemolysis is
usually achieved through the use of oral medications, although in some cases,
intravenous agents or even instillation of certain irrigating agents directly
onto the stone can be performed, using antegrade
nephrostomy
or
retrograde ureteral catheters.
Acetazolamide
(Diamox) is a medication that alkalinizes the urine. In addition to
acetazolamide or as an alternative, certain dietary supplements are available
that produce a similar alkalinization of the urine. These include
sodium bicarbonate,
potassium
citrate,
magnesium citrate, and Bicitra (a combination of
citric acid monohydrate and sodium citrate dihydrate). Aside from
alkalinization of the urine, these supplements have the added advantage of
increasing the urinary citrate level, which helps to reduce the aggregation of
calcium oxalate stones.
Increasing the urine pH to around 6.5 provides optimal conditions for
dissolution of uric acid stones. Increasing
the urine pH to a value higher than 7.0 increases the risk of calcium phosphate
stone formation. Testing the urine periodically with
nitrazine
paper can help to ensure the urine pH remains in this optimal range. Using this
approach, stone dissolution rate can be expected to be around 10 mm
(0.39 in) of stone radius per month.
Diuretics
One of the recognized medical therapies for prevention of stones is the
thiazide and
thiazide-like diuretics, such as
chlorthalidone
or
indapamide.
These drugs inhibit the formation of calcium-containing stones by reducing
urinary calcium excretion.
[1]
Sodium restriction is necessary for clinical effect of thiazides, as sodium
excess promotes calcium excretion. Thiazides work best for renal leak
hypercalciuria (high urine calcium levels), a condition in which high urinary
calcium levels are caused by a primary kidney defect. Thiazides are useful for
treating absorptive hypercalciuria, a condition in which high urinary calcium
is a result of excess absorption from the gastrointestinal tract.
Allopurinol
For people with hyperuricosuria and calcium stones,
allopurinol
is one of the few treatments that have been shown to reduce kidney stone
recurrences. Allopurinol interferes with the production of uric acid in the
liver. The drug is
also used in people with
gout or hyperuricemia (high serum uric acid levels). Dosage is
adjusted to maintain a reduced urinary excretion of uric acid. Serum uric acid
level at or below 6 mg/100 ml) is often a therapeutic goal.
Hyperuricemia is not necessary for the formation of uric acid stones;
hyperuricosuria can occur in the presence of normal or even
low serum
uric acid. Some practitioners advocate adding allopurinol only in people in
whom hyperuricosuria and hyperuricemia persist, despite the use of a
urine-alkalinizing agent such as sodium bicarbonate or potassium citrate.
Management
Medical
Stone size influences the rate of spontaneous stone passage. For example, up
to 98% of small stones (less than 5 mm (0.20 in) in diameter) may
pass spontaneously through urination within four weeks of the onset of
symptoms,but for larger stones (5 to 10 mm (0.20 to 0.39 in) in diameter), the
rate of spontaneous passage decreases to less than 53%. Initial stone location
also influences the likelihood of spontaneous stone passage. Rates increase
from 48% for stones located in the proximal ureter to 79% for stones located at
the vesicoureteric junction, regardless of stone size.
Assuming no
high-grade obstruction or associated infection is found in the urinary tract,
and symptoms are relatively mild, various nonsurgical measures can be used to
encourage the passage of a stone. Repeat stone formers benefit from more
intense management, including proper fluid intake and use of certain
medications. In addition, careful surveillance clearly is required to maximize
the clinical course for people who are stone formers.
Analgesia
Management of pain often requires intravenous administration of NSAIDs or
opioids.
Orally administered medications are often effective for
less severe discomfort.
Expulsion therapy
The use of medications to speed the spontaneous passage of ureteral calculi
is referred to as medical expulsive therapy.
[60]
Several agents, including
alpha adrenergic blockers (such as
tamsulosin)
and
calcium channel blockers (such as
nifedipine),
have been found to be effective.
[60]
A combination of tamsulosin and a
corticosteroid
may be better than tamsulosin alone.
[60]
These treatments also appear to be a useful adjunct to lithotripsy.
Surgical
Most stones under 5 mm (0.20 in) pass spontaneously.
[9][33]
Prompt surgery may, nonetheless, be required with persons with only one working
kidney, bilateral obstructing stones, a urinary tract infection and thus, it is
presumed, an infected kidney, or intractable pain.
[61]
Beginning in the mid-1980s, less invasive treatments such as extracorporeal
shock wave lithotripsy,
ureteroscopy, and
percutaneous nephrolithotomy began to
replace open surgery as the modalities of choice for the surgical management of
urolithiasis.
More recently, flexible ureteroscopy has been adapted
to facilitate retrograde nephrostomy creation for percutaneous nephrolithotomy.
This approach is still under investigation, though early results are favorable.
