k - 16 nephrolithiasis (bedah)
DESCRIPTION
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NEPHROLITHIASISEtiology, stone composition, medical management, and prevention
Urology Division, Surgery DepartmentMedical Faculty, University of Sumatera Utara
Epidemiology
Prevalence 2-3%, maybe in mountainous, desert & tropical areas
: = 3 : 1 25% stone formers have a family history Uric acid and Ca stones more frequent
in, infectious stones more common in The most common kinds of stones are
calcium oxalate, uric acid, struvite and cysteine
Composition of renal stones
Calcium oxalate 36 – 70% Calcium phosphate (hydroxyapatite) 6 –
20% Mixed Ca oxalate & Ca phosphate 11 – 31% Magnesium ammonium phosphate (struvite)
6 – 20% Uric acid 6 – 17% Cystine 0.5 – 3% Miscellaneous (xanthine, silicates & drug
metabolites) 1 – 4%
Factors influencing stone formation Genetics 1. Idiopathic hypercalciuria 2. Cystinuria 3. Primary hyperoxaluria, type 1 & 2 4. Lesch-Nyhan syndrome is an X-linked disease causing hyperuricemia 5. Familial renal tubular acidosis , Ehlres-
Danlos syndrome, Marfan’s syndrome, Wilson’s
disease
Environmental 1. Dietary factors - >> protein & sodium intake risk Ca
stone - >> purine diets urine pH
hyperuricosuria - B6 deficiency formation & excretion
oxalate - dehydration, inadequate fluid intake, vit C
excess, Ca supplements, Ca-containing antacids
2. Geographical factors - higher during summer months - higher in southeast United States
and lower in Mid-Atlantic and Northwest
regions
Stone formation
Crystallization - stone salts that precipitate out of urine
- the point of saturation of a salt in solution is called the
solubility product (Ksp)
- when the product of the components of a salt (e.g. calcium and oxalate) exceeds Ksp, salt crystals will
precipitate out of solution - crystallization is based on Ksp, pH, and the presence
of stone inhibitors and promoters
Nucleation - is the process by which stones form around a core, or nucleus - homogeneous stone nuclei form in solution - heterogeneous stone nuclei form around existing structures, such as cellular debris Aggregation - crystals join together to form larger clumps
TYPES OF STONE
CALCIUM OXALATE Recommended treatment : - absorptive : Ca restriction, sodium
cellulose phosphate, thiazides, fluid intake - other types : thiazide & fluid intake
URIC ACID STONES
5-10% of all stone Urine pH < 5.5 Associated with uric acid in urine, not
necessarily associated with hyperuricemia Secondary causes : gout (20%), chemoth/ for
myeloproliferative cancer Most common radioluscent
Th/ : dissolve : - fluids, alkali (citrate th/), allopurinol, protein
restriction - aim urine output > 2500 ml/day - potassium citrate or sodium bicarbonate achieve urine pH 6.5-7.0 avoid pH >7.0 can precipitate ca phosphate - if hyperuricemic or hyperuricosuric allupurinol
STRUVITE STONES
Composed of Mg ammonium phosphate crystals
= infection stones or triple phosphate stone Staghorn calculi are typically struvite stone Caused by infection with urease-producing
bacteria : - proteus id the most common
- urease hydrolized urea to form ammonia alkalinizes the urine, pH and allows
crystals to form
Urine pH will be >7.2 Th/ : - surgery - AB to prevent infection / stone
recurrence - irrigation with acidic solution successful but requires lengthy,
complicated treatment and costs danger : risk of sepsis, hypermagnesemia
- acetohydroxamic acid : inhibit urease; 20-70% severe side effect
CYSTINE STONES
1% of all stones Congenital disorders, autosomal recessive Caused by a defect in cystine reabsorption
in the proximal tubule Cystine poorly soluble at normal pH (pKa
8.3) Crystal form benzene ring on
microscopy
Th/ : - low methionine / sodium diet - hydrate to 3 L urine output/day - alkalinize urine : potassium citrate complex cystine - ESWL not effective
CALCIUM PHOSPHATE STONE
- urine pH > 5.5 - hypocitraturia - 70% of adults with type 1 Renal
Tubular Acidosis have stones - 80% are women - associated with renal cyst
Inhibitors of CaPO4 crystallization : - Mg - pyrophosphate - citrate - nephrocalcin Th / : - potassium bicarbonate or potassium citrate correct acidosis & urine citrate - fluids - thiazides if hypercalciuric
OTHER STONES
Dihydroxyadenine radioluscent Xanthine radioluscent Matrix radioluscent Ammonium acid urate Triamterene Indinavir radioluscent
MEDICAL MANAGEMENT
DIETARY PREVENTION - fluids : urine output stone formation if possible maintain >2.5 L urine/day - coffee, tea, beer, wine stone risk - lemon juice urinary citrate risk - grapefruit juice risk
PROTEIN - dietary protein urine Ca/uric acid/oxalate & urine citrate low/moderate protein intake is desirable
CALCIURIA - except in case of absorptive hypercalciuria, Ca binds intestinal oxalate prevent its
absorption - unless absorptive hypercalciuria maintain adequate calcium intake
SODIUM - dietary sodium urinary sodium
has not been proven to stone risk sodium in moderation
ASCORBIC ACID (VITAMIN C) - metabolized to oxalate - vit C intake urinary oxalate - advice : vitamin C in moderation
OXALATE - tea, instant coffee, spinach, chocolate, nuts
oxalate (+) increase urinary oxalate - high-oxalate foods in moderation for Ca oxalate
stone former
PHARMACOLOGICAL PREVENTION
THIAZIDES - HCT 25-50 mg or chlorthalidone
12.5-25 mg (up to 100mg) - start with small dose, titrate as needed
CITRATE - Inhibits Ca oxalate crystallization
- effective for hypocitraturic stone disease - potassium citrate 10-20 mEq w/meals - side effects : GI intolerance
ALLOPURINOL - inhibits xanthine oxidase & uric acid prod
- use in uric acid & hyperuricosuric Ca oxalate stone
- 300 mg/o, max 800 mg - dose in renal failure
PHOSPHATE (ORTHOPHSOPHATE) - vit D level urinary Ca excretion - urine pyrophosphate & citrate - clinical benefits are uncertain
MAGNESIUM - urinary citrate - clinical benefits uncertain
SODIUM CELLULOSE PHOSPHATE - binds Ca in the gut and inhibits absorption - indicated for use in absorptive
hypercalciuria - 5 g with meals
ANTIBIOTICS - long-term prophylaxis for struvite stone
after surgical treatment - drug should be culture specific
SUMMARY
The most common type is calcium oxalate. Uric acid stones form at pH <5.5. Uric acid stones form at pH <5.5. Primary
treatment and prevention is to alkalinize to alkalinize the urinethe urine; surgery is also an option
Struvite stone are composed of magnesium ammonium phosphate crystals. They are classically caused by infection with a urease-producing infection with a urease-producing bacteriumbacterium. Urinary pH is >7.2. treatment is surgery & antibioticssurgery & antibiotics
Cystine stones caused by a congenital autosomal recessive disorder.
Treatment : urinary alkalinization urinary alkalinization Calcium phosphate stones associated
with type 1 RTA Dietary interventions to prevent stones
include fluid intake, protein intake and sodium intake
Pharmacological interventions to prevent stones include thiazides, citrate, allopurinol, sodium cellulose phosphate
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