because they need antepartum fetal surveillance testing and may require delivery before their EDD (expected date of delivery).
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Chapter - 24
Kidney stones (Urolithiasis)
A kidney stone is a small stone, usually made up of calcium crystals, that forms inside the part of the kidney where urine collects. It may be found in the bladder, kidney, ureter or urethra. The stone usually causes little problem until it falls into the ureter, the tube that drains the kidney into the bladder, and causes an obstruction, preventing urine from draining out of the kidney and often causing severe pain. One of the roles of the kidney is to remove waste from the body by filtering blood and making urine. That urine flows from the kidney into the bladder through the ureter, a thin tube that connects the two. A variety of minerals and chemicals are excreted in the urine and sometimes these combine to form the beginning of a stone. Over time, this can grow from an invisible speck of sand into a stone that can be an inch in diameter or larger. These stones are known as different terms depending upon where they are located within the urinary tract as urolith (a stone anywhere within the urinary tract), nephrolith (a stone within the kidney), ureterolith (a stone within the ureter) and calculus (a stone within the body).
Kidney stones typically leave the body by passage in the urine stream, and many stones are formed and passed without causing symptoms. If stones grow to sufficient size (usually at least 3 millimeters (0.12 in)) they can cause obstruction of the ureter. Ureteral obstruction causes postrenal azotemia and hydronephrosis (distension and dilation of the renal pelvis and calyces), as well as spasm of the ureter. This leads to pain, most commonly felt In the flank (the area between the ribs and hip), lower abdomen, and groin (a condition called renal colic). Renal colic can be associated with nausea, vomiting, fever, blood in the urine, pus in the urine, and painful urination. Kidney stones affect all geographical, cultural, and racial groups. The lifetime risk is about 10 to 15% in the developed world, but can be as high as 20 to 25% in the Middle East. The increased risk of dehydration in hot climates, coupled with a diet 50% lower in calcium and 250% higher in oxalates compared to Western diets, accounts for the higher net risk in the Middle East. In the Middle East, uric acid stones are more common than calcium-containing stones The number of deaths due to kidney stones is estimated at 19.000 per year being fairly consistent between 1990 and 2010. In North America and Europe, the annual incidence (number of new cases per year) of kidney stones is roughly 0.5%. In the United States, the prevalence (frequency in the population) of urolithiasis has increased from 3.2% to 5.2% from the mid-1970s to the mid-1990s. Men most commonly experience their first episode between 30 and 40 years of age, whereas for women, the age at first presentation is somewhat later. Although kidney stones do not often occur in children, the incidence is increasing. These stones are in the kidney in two thirds of reported cases, and in the ureter in the remaining cases. Older children are at greater risk independent of age and sex - As with adults, most pediatric kidney stones are predominantly composed of calcium oxalate; struvite and calcium phosphate stones are less common. Calcium oxalate stones in children are associated with high amounts of calcium, oxalate, and magnesium in acidic urine.
* Classification of Kidney stones
Kidney stones are typically classified by their location and chemical composition.
Kidney
Stone type Population Circumstances Details
Calcium oxalate 80% When urine is alkaline (ph>5.5) 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 5-10% When urine is alkaline (hight 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 1-2%[41] 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.
* Sign and Symptoms
A kidney stone does not usually cause symptoms when it remains in the kidney.
There, they can sometimes become infected leading to serious kidney infection called pyelonephritis. When kidney stone passes from the urine collecting system within the kidney into the ureter, it can act like a dam. preventing easy flow of urine from the kidney into the bladder. This causes urine to back up, increasing pressure and swelling within the kidney.
Pain from a kidney stone can be excruciating, particularly as the stone is passing through the ureter. Kidney stone pain of this type is referred to as renal colic and its intensity is often described as akin to the pain of childbirth. The pain often begins in the back or flank of the side of the low back. It may radiate to the front of the abdomen and, in males, may cause testicular or scrotal pain. The pain is often intermittent in waves causing the affected individual to writhe or move constantly to find a comfortable position. There can be associated nausea, vomiting and sweating. The intense pain can be continuous or it can wax and wane as the stone passes toward the bladder. Often, in between the intense pain phase, there remains a dull ache in the back or flank. Once the stone passes into the bladder, the obstruction is relieved, urine can flow freely and the pain resolves. The dull flank ache can remain for a few hours or days after the stone has passed. Since the urethra is much wider than the ureter, passing the stone while urinating is usually not an issue and most patients cannot tell when they have eliminated the stone from their bladder. The quantity and severity of pain is not related to the size of the stone but rather the amount of obstruction and kidney swelling present. Sometimes, there can be blood visible in the urine as the kidney stone passes and irritates the lining of the urinary tract. Most often, the urine is clear to the naked eye and red blood cells are only visible in the urine when it
is analyzed under the microscope.
* Causes it isn’t exactly clear what causes kidney stones to form in some people and not others. Usually it requires concentrated urine that allows minerals like calcium to come in close contact with each other. Changes in the acid-base balance (pH) of the urine, how concentrated it is, and the concentration of minerals and chemicals within the urine are all factors that can begin the formation of a stone.
*Heredity-Family history may show that some of the blood relations of a patient with kidney stone had similar problem.
* Climate-In warm climates, the urine volume is low and concentrated with urates, oxalales and calcium salts. The occurrence of acute episodes of renal colic (kidney stone pain) is higher during hot rather cold weather. During hot weather, less urine is formed as more water is lost through perspiration. It is also claimed that during hot weather, with exposure of sun, more vitamin D is formed, which increases absorption of calcium from the gut and thus leads to increased urinary calcium excretion. People who work directly under the sun and perspire a lot may pass concentrated urine.
* Urinary tract infection (UT1)-Frequent infection of urinary tract may be contributory in that pus cells and epithelial cells may form a focus around which the stone may be formed.
* Reeumbcncy-Prolonged bed rest, particularly when a patient is immobilized, leads to generalized decalcification of bones. The breakdown products of bones are excreted through the urine, and may form stones.
* Dietary habits-Persons consuming foods rich in oxalates, calcium, purines and phosphate may predispose to formation of renal calculi. Excessive consumption of tea may also be a contributing factor. The metabolites excreted in the urine are significantly altered by the vitamin content of the diet. The administration of tryptophan increases, while vitamin B6 decreases, urinary oxalate excretion. Excessive urinary excretion of calcium predisposes to formation of calcium stones. Vitamin D increases calcium absorption from the intestinal tract. Excessive vitamin D and calcium administered indiscriminately over a prolonged period to growing children or pregnant and lactating mothers may result in stone formation. In areas in the tropics where calcium content of water is high, and vitamin D is formed by exposure of skin to sunlight, a considerable amount of calcium is absorbed.
* Dehydration-Crystals can form the beginning of the stone and eventually grow large enough to cause problems. Concentrated urine often occurs during an episode of dehydration, setting the stage for the beginning of stone formation. The consequences of that stone, when it is large enough to cause an obstruction, may occur weeks, months, or years later.
* Primary hyperparathyroidism-Parathyroid hormone increases the synthesis of 1.25-dihydroxy vitamin D3(calcitriol). Which increases calcium absorption in the intestine and reabsorption from the kidney tubule. The resulting high serum calcium reduces reabsorption of phosphorus and increases phosphate excretion by the kidneys. The consequent low serum phosphorus increases calcitriol production. The inorganic calcium and phosphorus resulting from excessive breakdown of the cementing matrix of bone are concentrated in the urinary tract and may from stones.
* Congenital malformation, stasis and infections-Urinary stones are not rare in young children and a high proportion of structural or metabolic abnormalities are found in them. Congenital malformation of the renal pelvis, ureter or bladder; stasis due to stricture or prostatic enlargement and UTI all predispose to stone formation.
* Other causes-High dietary intake of animal protein, sodium, refined sugars, fructose and high fructose corn syrup, oxalates, grapefruit juice and apple juice increase the risk of kidney stone formation. Kidney stones can result from an underlying metabolic condition, such as distal renal tubular acidosis. Dent’s disease, hyperparathyroidism, primary hyperoxaluria or medullary sponge kidney. 3-20% of people who form kidney stones have medullary sponge kidney. Kidney stones are more common in people with Corhn’s disease Crohn’s which is associated with hyperoxaluria and malabsorption of magnesium. A person with recurrent kidney stones may be screened for such disorders. This is typically done with a 24-hour urine collection. The urine is analyzed for features that promote stone formation. The diagnosis of kidney stones is made on the basis of information obtained from the history, physical examination, urinalysis and radiographic studies. Ultrasound examination and blood tests may also aid in the diagnosis.
* Having adequate water-All patients with kidney stones should be advised to drink sufficient water to keep the urine volume above 2 litres per day. By keeping well hydrated and drinking adequate amounts of water, most kidney stones can be prevented. For those patients who develop kidney stones because of underlying medical conditions, the addition of diet modification or chronic medication may be helpful. It is also essential to hydrate to increase the amount of urine produced to prevent any beginning of a stone. The primary reason for increasing fluid intake is to prevent formation of concentrated urine, in which crystals are more likely to combine and precipitate.
* Medication and surgery-The treatment for the renal colic of a kidney stone includes pain control and hydration. For severe pain, some patients present to the emergency department and often receive intravenous medications including narcotics, anti-inflammatory medications, and medications to control vomiting. In the uncomplicated situation, the stone may be allowed to pass on its own and it may take 2 to 3 weeks or longer. However, there are certain situations where more urgent action may be required. In patients with a solitary kidney, a kidney stone causing obstruction may lead to kidney failure and emergent referral to an urologist may be required to remove the stone or place a stent to bypass it. The type of procedure depends upon the location of the stone. Patients with obstructing kidney stones who develop urinary tract infection may need to have a stent or nephrostomy placed to prevent progression of the infection. Urine that is infected that cannot drain will act like an abscess and can cause the patient to become quite ill, often with fevers and chills. Large stones that are located in the kidney or the
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