Renal calculi

Renal calculi: Excerpt from Handbook of Diseases

Although renal calculi (kidney stones) may form anywhere in the urinary tract, they usually develop in the renal pelvis or the calyces of the kidneys. Such formation follows precipitation of substances normally dissolved in the urine (calcium oxalate, calcium phosphate, magnesium ammonium phosphate or, occasionally, urate or cystine).

Renal calculi vary in size and may be solitary or multiple. They may remain in the renal pelvis or enter the ureter and may damage renal parenchyma; large calculi cause pressure necrosis. In certain locations, calculi cause obstruction, with resultant hydronephrosis, and tend to recur.

Among Americans, renal calculi develop in 2 in 1,000 people and are more common in men than in women.

Causes

Although the exact cause of renal calculi is unknown, some patients develop them as a result of genetic factors. Predisposing factors include the following:

❑ Dehydration and resultant decreased urine production causes calculus-forming substances to become concentrated.

❑ Infection in tissue provides a site for calculus development; and pH changes provide a favorable medium for calculus formation (especially for magnesium ammonium phosphate or calcium phosphate calculi). Infected calculi (usually magnesium ammonium phosphate or staghorn calculi) may develop if bacteria serve as the nucleus in calculus formation. Such infections may promote destruction of renal parenchyma.

❑ Obstruction can result from urinary stasis (as in immobility from spinal cord injury), which allows calculi components to collect and adhere, forming calculi. Obstruction also promotes infection, which, in turn, compounds the obstruction.

❑ Metabolic factors that can predispose to renal calculi include hyperparathyroidism, renal tubular acidosis, elevated uric acid levels (usually with gout), defective metabolism of oxalate, genetic defect in metabolism of cystine, and excessive intake of vitamin D or dietary calcium.

Signs and symptoms

Signs and symptoms vary with size, location, and cause of the calculi.

Pain

Pain, the key symptom, usually results from obstruction; large, rough calculi occlude the opening to the ureter and increase the frequency and force of peristaltic contractions. The pain of classic renal colic travels from the costovertebral angle to the flank, to the suprapubic region and external genitalia.

The intensity of this pain fluctuates and may be excruciating at its peak. If calculi are in the renal pelvis and caly-ces, pain may be more constant and dull. Back pain (from calculi that produce an obstruction within a kidney) and severe abdominal pain (from calculi traveling down a ureter) may also occur. Nausea and vomiting usually accompany severe pain.

Accompanying signs and symptoms

Other associated signs and symptoms include fever, chills, hematuria (when calculi abrade a ureter), abdominal distention, pyuria and, rarely, anuria (from bilateral obstruction or unilateral obstruction in the patient with one kidney).

Diagnosis

The complete clinical picture along with the following diagnostic tests allows a diagnosis:

❑ Excretory urography, retrograde pyelography, abdominal computed tomography scan, or abdominal or kidney magnetic resonance imaging reveals tumors or obstructions of the ureter. These tests help confirm the diagnosis and determine size and location of calculi.

❑ Kidney-ureter-bladder X-rays reveal most renal calculi.

❑ Calculus analysis shows mineral content.

❑ Kidney ultrasonography, an easily performed noninvasive, nontoxic test, helps detect obstructive changes, such as unilateral or bilateral hydronephrosis.

❑ Urine culture of midstream specimen may indicate urinary tract infection.

❑ Urinalysis may be normal or may show increased specific gravity and acid or alkaline pH suitable for different types of stone formation. Other urinalysis findings include hematuria (gross or microscopic), crystals (urate, calcium, or cystine), casts, and pyuria with or without bacteria and white blood cells.

❑ A 24-hour urine collection is evaluated for calcium oxalate, phosphorus, and uric acid excretion levels.

❑ Serial blood calcium and phosphorus levels help detect hyperparathyroidism and show an increased calcium level in proportion to the normal level of serum protein.

❑ Blood protein level measures the level of free calcium unbound to protein.

❑ Blood chloride and bicarbonate levels may show renal tubular acidosis.

❑ Increased blood uric acid levels may indicate gout as the cause.

Diagnosis must rule out appendicitis, cholecystitis, peptic ulcer, and pancreatitis as potential sources of pain.

Treatment

Because 90% of renal calculi are smaller than 5 mm in diameter, treatment usually consists of measures to promote natural passage. Along with vigorous hydration, such treatment includes antimicrobial therapy (varying with the cultured organism) for infection; an analgesic, such as meperidine, for pain; and a diuretic to prevent urinary stasis and further calculus formation. (Thiazides decrease calcium excretion into the urine.)

Prophylaxis to prevent calculus formation includes a low-calcium diet for absorptive hypercalciuria, parathyroidectomy for hyperparathyroidism, and allopurinol and urinary alkalinization for uric acid calculi.

Medications may be given to decrease calculi formation or aid in the breakdown and excretion of the material causing the calculi. These include medications such as diuretics, phosphate solutions, allopurinol (for uric acid calculi), antibiotics (for struvite calculi), and medications that alkalinize the urine, such as sodium bicarbonate or sodium citrate.

Calculi too large for natural passage may require surgical removal. When a calculus is in the ureter, a cystoscope may be inserted through the urethra and the calculus manipulated with catheters or retrieval instruments. A small-diameter telescope, the ureteroscope, may be inserted through the ureter to remove calculi from the ureter and kidney. Extraction of calculi from other areas (such as the kidney calyx or renal pelvis) rarely necessitates a flank or lower abdominal approach.

Percutaneous ultrasonic lithotripsy and extracorporeal shock-wave lithotripsy shatter the calculus into fragments for removal by suction or natural passage. To prevent recurrence of calculi, the patient will also need teaching before discharge. (See Preventing recurrence of renal calculi.)

Special considerations

❑ To aid diagnosis, maintain a 24- to 48-hour record of urine pH with nitrazine pH paper, strain all urine through gauze or a tea strainer, and save all solid material recovered for analysis.

❑ To facilitate spontaneous passage, encourage the patient to walk, if pos-sible. To help prevent future stones, promote sufficient intake of fluids to maintain a urine output of 3 to 4 L/day (urine should be very diluted and colorless).

CLINICAL TIP: Use caution in patients with a history of cardiac disease because they may not be able to tolerate these large volumes of fluid.

❑ To help acidify urine, offer fruit juices, particularly cranberry juice. If the patient can’t drink the required amount of fluid, supplemental I.V. fluids may be given. Record intake and output and daily weight to assess fluid status and renal function.

❑ Stress the importance of proper diet and compliance with drug therapy. For example, if the patient’s stone was caused by a hyperuricemic condition, advise the patient or whoever prepares his meals which foods are high in purine.

❑ If surgery is necessary, provide reassurance. The patient is apt to be fearful, especially if surgery involves removing a kidney, so emphasize that the body can adapt well to having one kidney. If he’s to have an abdominal or flank incision, teach deep-breathing and coughing exercises.

❑ After surgery, the patient will probably have an indwelling urinary catheter or a nephrostomy tube in place. Unless a kidney was removed, expect bloody drainage from the catheter.

❑ Check dressings regularly for bloody drainage, and know how much drainage to expect. Watch closely for signs of suspected hemorrhage (such as excessive drainage and rising pulse rate). Use sterile technique when changing dressings or providing catheter care.

❑ Watch for signs and symptoms of infection (such as rising fever and chills), and give an antibiotic as needed.

❑ To prevent pneumonia, encourage frequent position changes and ambulation as soon as possible. Have him hold a small pillow over the operative site to splint the incision and thereby facilitate deep-breathing and coughing exercises.

Pictures

Book Source Details

• Book Title: Handbook of Diseases
• Author(s): Springhouse
• Year of Publication: 2003
• Copyright Details: Handbook of Diseases, Copyright © 2003 Lippincott Williams & Wilkins.

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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: Handbook of Diseases Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2003 ISBN: 1-58255-266-5

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