CHAPTER 22 Renal Disorders 547
will pass spontaneously with administration of large amounts of fluid to increase urine volume. Patients are instructed to drink at least 3 liters of fluid a day and strain all urine. If the patient cannot pass the stone, extracorporeal shock wave lithotripsy (ESWL) is often used. Lithotripsy utilizes sound waves to break up the stone into smaller particles to facilitate pas- sage. If lithotripsy is unsuccessful, ureterocystoscopic surgery may be necessary. A major treatment goal in the patient with neph- rolithiasis is to prevent recurrence, and this is largely dependent on determining the stone composition. Dietary changes may be necessary. High doses of thi- azide diuretics can reduce the risk of calcium stone formation. Allopurinol can also prevent formation of calcium stones. Citrate supplementation in the form of potassium citrate can prevent calcium, uric acid, and cystine stone formation. Calcium phosphate, calcium carbonate, and magne- sium phosphate stones develop in alkaline urine; when this occurs, the urine is kept acidic. Uric acid, cystine, and calcium oxalate stones precipitate in acidic urine; in this situation, the urine should be kept alkaline or less acidic than normal. Meat and cranberry juice can keep the pH of urine acidic. A diet rich in citrus fruits, legumes, and vegetables raises the pH and produces urine that is more alkaline. Complications Infection is one complication that may develop related to damage to renal tissue and urinary stasis. With a UTI, there is a risk for pyelonephritis or uro- sepsis. Although uncommon, with bilateral stones, renal damage caused by scarring from stone formation may lead to acute or chronic kidney disease. Hydrone- phrosis is a serious complication that occurs because of complete obstruction of urine outflow that causes urine to back up into the renal pelvis and destroy kidney tissue. Pyelonephritis Pyelonephritis is an infection of the renal pelvis and interstitium. It can be either acute or chronic and is most often caused by bacteria that ascend from the lower urinary tract. Epidemiology The estimated annual incidence of pyelonephritis is 459,000 to 1,138,000 cases in the United States. Generally, the percentage of patients who are hospi- talized is lower than 20% among young women but higher among young children and adults older than 65 years. The incidence is higher in young women, commonly related to lower UTI. The rate increases in older males and is attributed to increased incidence of prostate enlargement, which can obstruct urine out- flow. Approximately 20% to 30% of pregnant women develop pyelonephritis.
Etiology Risk factors for lower urinary tract infection such as sexual activity, new sexual partner, spermicide expo- sure, and history of UTI, also confer a predisposition to pyelonephritis. However, less than 3% of cases of cystitis and asymptomatic bacteriuria progress to pyelonephritis. Pyelonephritis usually occurs when bacteria from the GI tract enter the bladder and ascend to the kidneys. The anatomical proximity of the anus and urethra in women increases risk of urinary tract infection. Pyelonephritis also commonly occurs if there is obstruction somewhere in the renal system, also referred to as obstructive uropathy. Obstructive urop- athy can be caused by calculi in the ureter, tumor, or pregnancy. Whenever there is obstructed outflow of urine, the stagnant urine acts as a medium for bacte- rial growth, which can ascend into the kidney to cause pyelonephritis. An anatomical abnormality called vesicoureteral reflux is a common predisposing factor for pyelo- nephritis. Reflux of urine occurs from the bladder into the ureter. The refluxed urine acts as a medium for bacterial growth, which leads to ascending bac- terial infection (see Fig. 22-13). Neurogenic bladder is another condition that predisposes individuals to ascending bacterial infection and pyelonephritis. Neurogenic bladder occurs in patients with condi- tions such as multiple sclerosis, spinal cord injury, or transection of pelvic parasympathetic nerves. Because of the lack of neurological control of the bladder, the patient is unable to empty the bladder completely, and urine retention is common. The retained urine acts as a medium for bacterial growth, and ascending infec- tion leads to pyelonephritis. Another risk factor for pyelonephritis is urolog- ical instrumentation with catheters or cystoscopes.
Reflux of urine up from bladder into ureters
Urine can back up into the renal pelvis in severe reflux.
Kidney
Vesicoureteral valve stays open.
Ureter
Bladder
Urethra
FIGURE 22-13. Vesicoureteral reflux (VUR). Urine should flow in one direction—down from the kidneys, through the ureters, to the bladder. VUR is the abnormal flow of urine from the bladder back up into the ureters.
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