Nephrolithiasis Treatment & Management

Treatment of nephrolithiasis involves emergency management of renal (ureteral) colic, including surgical interventions where indicated, and medical therapy for stone disease.

In emergency settings where concern exists about possible renal failure, the focus of treatment should be on correcting dehydration, treating urinary infections, preventing scarring, identifying patients with a solitary functional kidney, and reducing risks of acute renal failure from contrast nephrotoxicity, particularly in patients with preexisting azotemia (creatinine >2 mg/dL), diabetes, dehydration, or multiple myeloma. Adequate intravenous (IV) hydration is essential to minimize the nephrotoxic effects of IV contrast agents. Choosing imaging studies that do not require IV contrast (eg, ultrasonography, plain abdominal flat plate radiographs, noncontrast computed tomography [CT] scans) is wise, especially in patients at increased risk for developing renal failure.

Most small stones with relatively mild hydronephrosis can be treated with observation and acetaminophen. More serious cases with intractable pain may require drainage with a stent or percutaneous nephrostomy. The internal ureteral stent is usually preferred in these situations because of decreased morbidity.

Acetaminophen can be used in pregnancy for mild-to-moderate pain. Opioid drugs, such as morphine and meperidine, are pregnancy category C medications, which means they can be used but they cross the placental barrier. Opioids can cause respiratory depression in the fetus; therefore, they should not be used near delivery or when other medications are adequate.

A stone chemical composition analysis should be performed whenever possible, and information should be provided to motivated patients about possible 24-hour urine testing for long-term nephrolithiasis prophylaxis. This is particularly important in patients with only 1 functioning kidney, those with medical risk factors, and children. However, any strongly motivated patient can benefit from a prevention analysis and prophylactic treatment if they are willing to pursue long-term therapy.

The size of the stone is an important predictor of spontaneous passage. A stone less than 4 mm in diameter has an 80% chance of spontaneous passage; this falls to 20% for stones larger than 8 mm in diameter. However, stone passage also depends on the exact shape and location of the stone and the specific anatomy of the upper urinary tract in the particular individual. For example, the presence of a ureteropelvic junction (UPJ) obstruction or a ureteral stricture could make passing even very small stones difficult or impossible. Most experienced emergency department (ED) physicians and urologists have observed very large stones passing and some very small stones that do not move.

Aggressive medical therapy has shown promise in increasing the spontaneous stone passage rate and relieving discomfort while minimizing narcotic usage. Aggressive treatment of any proximal urinary infection is important to avoid potentially dangerous pyonephrosis and urosepsis. In these cases, consider percutaneous nephrostomy drainage rather than retrograde endoscopy, especially in very ill patients.

Medical therapy for stone disease takes both short- and long-term forms. The former includes measures to dissolve the stone (possible only with noncalcium stones) or to facilitate stone passage, and the latter includes treatment to prevent further stone formation. Stone prevention should be considered most strongly in patients who have risk factors for increased stone activity, including stone formation before age 30 years, family history of stones, multiple stones at presentation, and residual stones after surgical treatment.

Indications for hospitalization

The decision to hospitalize a patient with a stone is usually made based on clinical grounds rather than on any specific finding on a radiograph. Generally, hospitalization for an acute renal colic attack is now officially termed an observation because most patients recover sufficiently to go home within 24 hours. Admission rate for patients with acute renal colic is approximately 20%.

Hospital admission is clearly necessary when any of the following is present:

• Oral analgesics are insufficient to manage the pain.
• Ureteral obstruction from a stone occurs in a solitary or transplanted kidney.
• Ureteral obstruction from a stone occurs in the presence of a urinary tract infection (UTI), fever, sepsis, or pyonephrosis.

Infected hydronephrosis, defined as UTI proximal to an obstructing stone, mandates hospital admission for antibiotics and prompt drainage. Midstream urine culture and sensitivity was a poor predictor of infected hydronephrosis in one series, being positive in only 30% of cases.^[31]

The clinical presentation of infected hydronephrosis is variable. Pyuria (>5 white blood cells [WBCs] per high-power field [hpf]) is almost always present but is not diagnostic of proximal infection. In one small series of 23 patients with infected hydronephrosis, the temperature was higher than 38°C in 15 patients, the peripheral WBC count was more than 10 X 10⁹/L in 13 patients, and the creatinine level was greater than 1.3 mg/dL in 12 patients.^[32]

Renal ultrasonography or computed tomography (CT) may distinguish pyonephrosis from simple hydronephrosis by demonstrating a fluid-fluid level in the renal pelvis (urine on top of purulent debris). In 2 small studies, ultrasonographic sensitivity for pyonephrosis was found to be 62-67%. CT sensitivity for pyonephrosis has not been reliably determined.^{[33, 34]} The emergency physician must maintain a high index of suspicion.^[35]

Antibiotics should cover Escherichia coli and Staphylococcus, Enterobacter, Proteus, and Klebsiella species. In another small study of 38 patients with hydronephrosis, 16 had infected hydronephrosis and 22 had sterile hydronephrosis. Ultrasonography alone detected 6 of 16 cases of pyonephrosis, a sensitivity of 38%. Using a cutoff value of 3 mg/dL for C-reactive protein and 100 mm/h for erythrocyte sedimentation rate, the diagnostic accuracy of detecting infected hydronephrosis and pyonephrosis increased to 97%.^[36]

Relative indications to consider for a possible admission include comorbid conditions (eg, diabetes), dehydration requiring prolonged intravenous (IV) fluid therapy, renal failure, or any immunocompromised state. Patients with complete obstruction, perinephric urine extravasation, a solitary kidney, or pregnancy, and those with a poor social support system, also should be considered for admission, especially if rapid urologic follow-up is not reliably available.

Larger stones (ie, ≥ 7 mm) that are unlikely to pass spontaneously require some type of surgical procedure. In some cases, hospitalizing a patient with a large stone to facilitate surgical stone intervention is reasonable. However, most patients with acute renal colic can be treated on an ambulatory basis.

About 15-20% of patients require invasive intervention due to stone size, continued obstruction, infection, or intractable pain. Several techniques are available to the urologist when the stone fails to pass spontaneously, including extracorporeal shock wave lithotripsy (SWL), ureteroscopy, and percutaneous nephrolithotomy.^[37]

Initial treatment of a renal colic patient in the ED starts with obtaining IV access to allow fluid, analgesic, and antiemetic medications to be administered. Many of these patients are dehydrated from poor oral intake and vomiting. Although the role of supranormal hydration in the management of renal (ureteral) colic is controversial (see below), patients who are dehydrated or ill need adequate restoration of circulating volume.

After diagnosing renal (ureteral) colic, determine the presence or absence of obstruction or infection. Obstruction in the absence of infection can be initially managed with analgesics and with other medical measures to facilitate passage of the stone. Infection in the absence of obstruction can be initially managed with antimicrobial therapy. In either case, promptly refer the patient to a urologist.

If neither obstruction nor infection is present, analgesics and other medical measures to facilitate passage of the stone (see below) can be initiated with the expectation that the stone will likely pass from the upper urinary tract if its diameter is smaller than 5-6 mm (larger stones are more likely to require surgical measures).

If both obstruction and infection are present, emergency decompression of the upper urinary collecting system is required (see Surgical Care). In addition, immediately consult with a urologist for patients whose pain fails to respond to ED management.

Pain relief

The cornerstone of ureteral colic management is analgesia, which can be achieved most expediently with parenteral narcotics or nonsteroidal anti-inflammatory drugs (NSAIDs). If oral intake is tolerated, the combination of oral narcotics (eg, codeine, oxycodone, hydrocodone, usually in a combination form with acetaminophen), NSAIDs, and antiemetics, as needed, is a potent outpatient management approach for renal (ureteral) colic.

Parenteral narcotics are the mainstay of analgesia for patients with acute renal colic. They work primarily on the central nervous system (CNS) to reduce the perception of pain. They are inexpensive and quite effective. When considering a medication and dosage range, remember that acute renal colic is probably the most painful malady to affect humans. Adverse effects of narcotic analgesics include respiratory depression, sedation, constipation, a potential for addiction, nausea, and vomiting.

Choosing any particular agent tends to be somewhat arbitrary. Morphine, meperidine, and butorphanol are the most commonly used.

Morphine is a potent narcotic analgesic that controls severe pain primarily through a CNS mechanism via specific receptor site interactions. The usual dosage is 10 mg/70 kg body weight intramuscularly (IM) or subcutaneously (SC) every 4 hours. The actual dosage required varies according to each individual patient’s tolerance and severity of discomfort. For more rapid results, morphine sulfate can be administered IV in doses of 4-10 mg, but this must be done slowly or in small increments to avoid excessive adverse effects.

Adverse effects of morphine include respiratory depression, drowsiness, mood changes, nausea, vomiting, increases in the cerebrospinal fluid pressure, and cough reflex depression. The most bothersome is respiratory depression caused by a direct effect on the brain stem respiratory center. This effect is most severe in patients who are elderly, debilitated, or both.

Meperidine is a potent parenteral narcotic analgesic that is very similar in overall effect to morphine sulfate. A 60-80 mg dose of meperidine is roughly equivalent to 10 mg of morphine. Meperidine offers a slightly more rapid onset of action and slightly shorter duration of analgesic activity than morphine sulfate. Some evidence suggests that meperidine may have slightly fewer adverse effects than morphine.

The dosage range is usually 50-150 mg IM or SC every 3-4 hours; it is reduced by at least 50% with IV administration. The actual effective dosage varies according to the source of the pain and the individual’s tolerance. As with morphine sulfate, IV administration should be performed slowly. Meperidine is contraindicated in patients taking monoamine oxidase inhibitors.

Butorphanol has some theoretical advantages based on studies that suggest it causes less smooth muscle spasm and respiratory depression than either morphine or meperidine. Butorphanol costs approximately $10/mg, compared with approximately $0.05/mg for meperidine. Because 1 mg of butorphanol is roughly equivalent in pain relieving efficacy to 20 mg of meperidine, butorphanol effectively is about 10 times as costly.

Naloxone (0.4 mg or 1 mL) is a specific narcotic antagonist for both meperidine and morphine sulfate that can be administered to counteract inadvertent narcotic overdosage or unusual opioid sensitivity. Naloxone has no analgesic properties.

Nalbuphine is a potent parenteral analgesic that is partly antagonistic to narcotics. Its overall effectiveness in relieving pain is equivalent to the opioids. The usual starting dose is 0.5 mg IV or 1-1.5 mg IM every 4-6 hours as needed.

Of the NSAIDs, the only one approved by the US Food and Drug Administration (FDA) for parenteral use is ketorolac. Ketorolac works at the peripheral site of pain production rather than on the CNS. It has been proven in multiple studies to be as effective as opioid analgesics, with fewer adverse effects.^{[38, 39]} The dosage is 30-60 mg IM or 30 mg IV initially followed by 30 mg IV or IM every 6-8 hours. A dose of 15 mg is recommended in patients older than 65 years.

In more severe cases, ketorolac is particularly effective when used together with narcotic analgesics. Oral ketorolac is available in 10-mg pills, but the efficacy of this form in persons with acute renal colic is less clear. Some practitioners use parenteral ketorolac in the hospital but recommend either ibuprofen or oral cyclooxygenase-2 inhibitors (eg, celecoxib or meloxicam) for pain management in outpatients.

An intranasal ketorolac preparation is now available for moderate-to-severe pain and may be particularly useful for outpatient use in patients unable to take oral medication. A maximum of 5 days of ketorolac therapy is recommended.

Chemically, ketorolac is similar to aspirin and may increase the prothrombin time when administered with anticoagulants. Ketorolac can increase methotrexate toxicity and phenytoin levels. It is potentiated by probenecid and should be avoided in patients with peptic ulcer disease, renal failure, or recent gastrointestinal (GI) bleeding.

Antiemetic therapy

Because nausea and vomiting frequently accompany acute renal colic, antiemetics often play a role in renal colic therapy. Several antiemetics have a sedating effect that is often helpful.

Metoclopramide is the only antiemetic that has been specifically studied in the treatment of renal colic. In 2 double-blinded studies, it apparently provided pain relief equivalent to narcotic analgesics in addition to relieving nausea. Its antiemetic effect stems from its dopaminergic receptor blockage in the CNS. It has no anxiolytic activity and is less sedating than other centrally acting dopamine antagonists. The effect of metoclopramide begins within 3 minutes of an IV injection, but it may not take effect for as long as 15 minutes if administered IM.

The usual dose in adults is 10 mg IV or IM every 4-6 hours as needed. Metoclopramide is not available as a suppository.

Other medications commonly used as antiemetics include promethazine, prochlorperazine, and hydroxyzine. The author usually recommends antiemetics when patients with renal colic have been vomiting actively or report nausea sufficient to interfere with oral therapy. They also may be useful as anxiolytics in some cases. Whereas metoclopramide is the antiemetic of choice in the hospital or ED setting, a suppository formulation such as promethazine or prochlorperazine is recommended for outpatient use.

Antidiuretic therapy

Several studies have now demonstrated that desmopressin (DDAVP), a potent antidiuretic that is essentially an antidiuretic hormone, can dramatically reduce the pain of acute renal colic in many patients. It acts quickly, has no apparent adverse effects, reduces the need for supplemental analgesic medications, and may be the only immediate therapy necessary for some patients. It is available as a nasal spray (usual dose of 40 mcg, with 10 mcg per spray) and as an IV injection (4 mcg/mL, with 1 mL the usual dose). Generally, only 1 dose is administered.

Animal studies have demonstrated a significant reduction in mean intraureteral pressure after an acute obstruction in subjects administered desmopressin compared with controls. In human studies, approximately 50% of 126 patients tested had complete relief of their acute renal colic pain within 30 minutes after the administration of intranasal desmopressin without any analgesic medication. For patients in whom desmopressin therapy failed, suitable analgesics were administered. No adverse effects from the antidiuretic medication occurred.

Although desmopressin is thought to work by reducing the intraureteral pressure, it may also have some direct relaxing effect on the renal pelvic and ureteral musculature. A central analgesic effect through the release of hypothalamic beta-endorphins has been proposed but remains unproved. Whether this therapy significantly affects eventual stone passage is unknown.

While some of the human studies lack adequate controls and further studies must be conducted, desmopressin therapy currently appears to be a promising alternative or adjunct to analgesic medications in patients with acute renal colic, especially in patients in whom narcotics cannot be used or in whom the pain is unusually resistant to standard medical treatment.

Antibiotic therapy

Antibiotic use in patients with kidney stones remains controversial. Overuse of the more effective agents leaves only highly resistant bacteria, but failure to adequately treat a UTI complicated by an obstructing calculus can result in potentially life-threatening urosepsis and pyonephrosis.

Use antibiotics if a kidney stone or ureteral obstruction has been diagnosed and the patient has clinical evidence of a UTI. Evidence of a possible UTI includes an abnormal finding upon microscopic urinalysis, showing pyuria of 10 WBCs/hpf (or more WBCs than RBCs), bacteriuria, fever, or unexplained leukocytosis. Perform a urine culture in these cases because a culture cannot be performed reliably later should the infection prove resistant to the prescribed antibiotic.

Approximately 3% of patients being treated for renal colic are reported to develop a newly acquired UTI. While case numbers are not high, such an infection can dramatically complicate the clinical outcome for that patient. Base selection of the antibiotic on the patient’s presentation, reserving the most effective parenteral antibiotics for patients with frank sepsis or other high-risk characteristics.

The author’s preference for initial medical therapy for pain in patients with acute renal colic is to use IV or IM ketorolac for pain with metoclopramide for nausea. If this therapy is unsuccessful or if the case is deemed more severe, a narcotic such as morphine sulfate or meperidine is added as needed to control pain. An antibiotic is administered if any question of potential infection exists. An oral antibiotic is always used if the patient is able to return home.

Active medical expulsive therapy

The traditional outpatient treatment approach detailed above has recently been improved with the application of a more aggressive treatment approach known as active medical expulsive therapy (MET). Many randomized trials have confirmed the efficacy of MET in reducing the pain of stone passage, increasing the frequency of stone passage, and reducing the need for surgery.^{[40, 41, 42, 43, 44, 45, 46, 47]}

MET should be considered in any patient with a reasonable probability of stone passage. Given that stones smaller than 3 mm are already associated with an 85% chance of spontaneous passage, MET is probably most useful for stones 3-10 mm in size. Overall, MET is associated with a 65% greater likelihood of stone passage.^[48]

The original rationale for MET was based on the possible causes of failure to spontaneously pass a stone, including ureteral stricture, muscle spasm, local edema, inflammation, and infection. Various common drugs were considered that would potentially benefit these problems, improve spontaneous stone passage, and alleviate renal colic discomfort.

Although NSAIDs have ureteral-relaxing effects and, as such, can be considered a form of MET, patient outcomes have been significantly improved only with the use of more potent (off-label) medications. The initially popularized regimens for MET included corticosteroids such as prednisone, as in the following example:

• Ketorolac at 10 mg orally every 6 hours for 5 days
• Nifedipine XL at 30 mg/d PO for 7 days
• Prednisone 20 mg PO twice a day for 5 days
• Trimethoprim/sulfamethoxazole DS once a day for 7 days
• Acetaminophen 2 tablets 4 times a day for 7 days
• An oral opioid pain medication (oxycodone-acetaminophen) as needed for breakthrough pain
• Prochlorperazine suppository as needed for control of nausea

Although corticosteroids are effective, concerns about their side effects (admittedly not supported by randomized data) limited the acceptance of MET. More recently, randomized studies have demonstrated great efficacy of the following individual agents, sparing the corticosteroid component.

The calcium channel blocker nifedipine is indicated for angina, migraine headaches, Raynaud disease, and hypertension, but it can also reduce muscle spasms in the ureter, which helps reduce pain and facilitate stone passage. Ureteral smooth muscle uses an active calcium pump to produce contractions, so a calcium channel blocker such as nifedipine would be expected to relax ureteral muscle spasms.

The alpha-blockers, such as terazosin, and the alpha-1 selective blockers, such as tamsulosin, also relax the musculature of the ureter and lower urinary tract, markedly facilitating passage of ureteral stones. Some literature suggests that the alpha-blockers are more effective in this setting than the calcium channel blockers, and most practitioners currently use alpha-blockers preferentially over calcium channel blockers.

Multiple prospective randomized controlled studies in the urology literature have demonstrated that patients treated with oral alpha-blockers have an increased rate of spontaneous stone passage and a decreased time to stone passage.^{[41, 42, 43]} The best studied of these is tamsulosin, 0.4 mg administered daily.

A systematic review by Singh et al found that MET using either alpha antagonists or calcium channel blockers augmented the stone expulsion rate for moderately sized distal ureteral stones. Adverse effects were noted in 4% of those taking alpha antagonists and in 15.2% of those taking calcium channel blockers.^[49]

A systematic review by Beach et al found that MET with alpha antagonists for 28 days increased the rate of stone passage, decreased the time to stone passage, and decreased the rates of hospitalization and ureteroscopy, with minimal adverse effects.^[50]

Not all data support MET. A randomized study of 77 ED patients with ureterolithiasis found no benefit to a 14-day course of tamsulosin, though the study group was small and the average stone size was 3.6 mm, making spontaneous passage without MET highly likely.^[51]

MET with calcium channel blockers and alpha-blockers also appears to improve the results of ESWL (see Surgical Care) inasmuch as the stone fragments resulting from treatment appear to clear the system more effectively.

Analgesic therapy combined with MET dramatically improves the passage of stones, addresses pain, and reduces the need for surgical treatment. Ibuprofen can be substituted for the ketorolac tablets recommended in the original studies. Fewer complications with ibuprofen occur while maintaining efficacy for pain relief. An oral narcotic (eg, oxycodone/acetaminophen) is used as needed to control breakthrough pain.

• A typical regimen for this aggressive therapy is as follows:
• 1-2 oral narcotic/acetaminophen tablets every 4 hours as needed for pain
• 600-800 mg ibuprofen every 8 hours

MET with 30 mg nifedipine extended-release tablet once daily, 0.4 mg tamsulosin once daily, or 4 mg of terazosin once daily

Limit MET to a 10- to 14-day course, as most stones that pass during this regimen do so in that time frame. If outpatient treatment fails, promptly consult a urologist.

Future studies may identify a subgroup of patients such as those with larger stones or history of inability to pass stones that would benefit from MET.

Intravenous hydration

IV hydration in the setting of acute renal colic is controversial. Whereas some authorities believe that IV fluids hasten passage of the stone through the urogenital system, others express concern that additional hydrostatic pressure exacerbates the pain of renal colic. One small study of 43 ED patients found no difference in pain score or rate of stone passage in patients who received 2 L of saline over 2 hours versus those who received 20 mL of saline per hour.^[52]

IV hydration should be given to patients with clinical signs of dehydration or to those with a borderline serum creatinine level who must undergo intravenous pyelography (IVP).

Straining urine for stones

Collecting any passed kidney stones is extremely important in the evaluation of a patient with nephrolithiasis for stone-preventive therapy. Yet, in a busy ED, the simple instruction to strain all the urine for stones can be easily overlooked.

Knowing when a stone is going to pass is impossible regardless of its size or location. Even after a stone has passed, residual swelling and spasms can cause continuing discomfort for some time. Be certain that all urine is actually strained for any possible stones. An aquarium net makes an excellent urinary stone strainer for home use because of its tight nylon weave, convenient handle, and collapsible nature, making it very portable; it easily fits into a pocket or purse.

In general, stones that are 4 mm in diameter or smaller will probably pass spontaneously, and stones that are larger than 8 mm are unlikely to pass without surgical intervention. With MET, stones 5-8 mm in size often pass, especially if located in the distal ureter. The larger the stone, the lower the possibility of spontaneous passage (and thus the greater the possibility that surgery will be required), although many other factors determine what happens with a particular stone.

Indications and contraindications

The primary indications for surgical treatment include pain, infection, and obstruction. Infection combined with urinary tract obstruction is an extremely dangerous situation, with significant risk of urosepsis and death, and must be treated emergently in virtually all cases. Additionally, certain occupational and health-related reasons exist.

General contraindications to definitive stone manipulation include the following:

• Active, untreated UTI
• Uncorrected bleeding diathesis
• Pregnancy (a relative, but not absolute, contraindication)

Specific contraindications may apply to a given treatment modality. For example, do not perform SWL if a ureteral obstruction is distal to the calculus or in pregnancy.

Surgical options

For an obstructed and infected collecting system secondary to stone disease, virtually no contraindications exist for emergency surgical relief either by ureteral stent placement (a small tube placed endoscopically into the entire length of the ureter from the kidney to the bladder) or by percutaneous nephrostomy (a small tube placed through the skin of the flank directly into the kidney).

Many urologists have a preference for one technique or the other, but, in general, patients who are acutely ill, who have significant medical comorbidities, or who harbor stones that probably cannot be bypassed with ureteral stents undergo percutaneous nephrostomy, while others receive ureteral stent placement.

In patients who are floridly septic or hemodynamically unstable, a percutaneous nephrostomy is a faster and safer way to establish drainage of an infected and obstructed kidney. In these situations, retrograde approaches to drainage, if used at all, should be reserved for relatively mild cases in which patients are medically stable. Use appropriate urine cultures and antibiotics whenever a UTI is suspected in conjunction with hydronephrosis or renal colic.

The vast majority of symptomatic urinary tract calculi are now treated with noninvasive or minimally invasive techniques, while open surgical excision of a stone from the urinary tract is now limited to isolated atypical cases.

Guidelines are now available to assist the urologist in selecting surgical treatments. The 2005 American Urological Association (AUA) staghorn calculus guidelines recommend percutaneous nephrostolithotomy as the cornerstone of management.^[53] In the ureteral stone guidelines produced by a joint effort of the AUA and the European Association of Urology, SWL and ureteroscopy are both recognized as first-line treatments for ureteral stones.^[54]

Stent placement

Internal ureteral stents form a coil at either end when the stiffening insertion guide wire is removed. One coil forms in the renal pelvis and the other in the bladder. Stents are available in lengths from 20-30 cm and in 3 widths from 4.6F to 8.5F. Some are designed to soften after placement in the body; others are rather stiff to resist crushing and obstruction by large stones or external compression with occlusion from an extrinsic tumor or scar tissue.

To select the correct-size stent, estimates can be made based on the height of the patient, or the ureteral length can be measured. This is best performed by means of a retrograde pyelogram. The distance from the tip of the retrograde catheter to the UPJ is measured in centimeters with a tape measure. To account for the average magnification effect of the film, 10% of this reading is subtracted. If the result is an odd number, a double-J stent one size longer is used. The most common lengths used are 26 cm in men and 24 cm in women.

The optimal stent width depends on both the relative diameter and course of the ureter and the purpose of the stent. If the patient has a stricture or a tortuous ureter, a stiffer or larger-diameter stent is placed if possible.

When used for stone disease, stents perform several important functions. They virtually guarantee drainage of urine from the kidney into the bladder and bypass any obstruction. This relieves patients of their renal colic pain even if the actual stone remains. Over time, stents gently dilate the ureter, making ureteroscopy and other endoscopic surgical procedures easier to perform later.

Because they are also quite radiopaque, stents provide a stable landmark when performing SWL. A landmark is particularly important with small or barely visible stones, especially in the ureter, because the SWL machine uses radiographic visualization to target the stone.

Once large stones are broken up, stents tend to prevent the rapid dumping of large amounts of stone fragments and debris into the ureter (called steinstrasse). The stent forces the fragments to pass slowly, which is more efficient and prevents clogging.

Stents do have drawbacks. They can become blocked, kinked, dislodged, or infected. A KUB radiograph can be used to determine stent position, while infection is easily diagnosed by urinalysis. A renal sonogram can sometimes be helpful if there is concern for obstruction.

Questionable cases can be evaluated further using a radiographic cystogram or an IVP. The cystogram is performed by filling the urinary bladder with diluted contrast media through a Foley catheter under gravity pressure. A stent that is unclogged and functioning normally should show free reflux of contrast from the bladder into the stented renal pelvis.

The major drawback of stents, however, is that they are often quite uncomfortable for patients due to direct bladder irritation, spasm, and reflux. This discomfort can be alleviated to some extent by pain medications, anticholinergics (eg, oxybutynin, tolterodine), alpha-blockers, and topical analgesics (eg, phenazopyridine).

Percutaneous nephrostomy

In some cases, drainage of an obstructed kidney is necessary and stent placement is inadvisable or impossible. In particular, such cases include patients with pyonephrosis who have a UTI or urosepsis exacerbated by an obstructing calculus. In these patients, retrograde endourological procedures like retrograde pyelography and stent placement may exacerbate infection by pushing infected urinary material into the obstructed renal unit. Percutaneous nephrostomy is useful in such situations.^[55]

Extracorporeal shockwave lithotripsy

SWL, the least invasive of the surgical methods of stone removal, utilizes an underwater energy wave focused on the stone to shatter it into passable fragments.

It is especially suitable for stones that are smaller than 2 cm and lodged in the upper or middle calyx. It is contraindicated in pregnancy, untreatable bleeding disorders, tightly impacted stones, or in cases of ureteral obstruction distal to the stone. In addition, the effectiveness is limited for very hard stones (which tend to be dense on CT scan), cystine stones, and in very large patients.

The patient, under varying degrees of anesthesia (depending on the type of lithotriptor used), is placed on a table or in a gantry that is then brought into contact with the shock head. The deeper the anesthesia (general endotracheal), the better the results. In addition, evidence is mounting that slower shockwave delivery (60-80 per min) improves the results. New lithotriptors that have 2 shock heads, which deliver a synchronous or asynchronous pair of shocks (possibly increasing efficacy), have attracted great interest.

The shock head delivers shockwaves developed from an electrohydraulic, electromagnetic, or piezoelectric source. The shockwaves are focused on the calculus, and the energy released as the shockwave impacts the stone produces fragmentation. The resulting small fragments pass in the urine.

SWL is limited somewhat by the size and location of the calculus. A stone larger than 1.5 cm in diameter or one located in the lower section of the kidney is treated less successfully. Fragmentation still occurs, but the large volume of fragments or their location in a dependent section of the kidney precludes complete passage. In addition, results may not be optimal in large patients, especially if the skin-to-stone distance exceeds 10 cm.^[56]

Ureteroscopy

Along with SWL, ureteroscopic manipulation of a stone (see the image below) is a commonly applied method of stone removal. A small endoscope, which may be rigid, semirigid, or flexible, is passed into the bladder and up the ureter to directly visualize the stone.

Ureteroscopy is especially suitable for removal of stones that are 1-2 cm, lodged in the lower calyx or below, cystine stones, and high attenuation ("hard") stones. The typical patient has acute symptoms caused by a distal ureteral stone, usually measuring 5-8 mm. Stones smaller than 5 mm in diameter generally are retrieved using a stone basket, whereas tightly impacted stones or those larger than 5 mm are manipulated proximally for SWL or are fragmented using an endoscopic direct-contact fragmentation device.

Often, a ureteral stent must be placed after ureteroscopy in order to prevent obstruction from ureteral spasm and edema. Since a ureteral stent is often uncomfortable, many urologists eschew stent placement following ureteroscopy in selected patients.^[57]

Percutaneous nephrostolithotomy

Percutaneous nephrostolithotomy allows fragmentation and removal of large calculi from the kidney and ureter. Because of their increased morbidity compared with SWL and ureteroscopy, percutaneous procedures are generally reserved for large and/or complex renal stones and failures from the other 2 modalities. Percutaneous nephrostolithotomy is especially useful for stones larger than 2 cm in diameter.

A needle and then a wire, over which is passed a hollow sheath, are inserted directly into the kidney through the skin of the flank. Percutaneous access to the kidney typically involves a sheath with a 1-cm lumen, which will admit relatively large endoscopes with powerful and effective lithotrites that can rapidly fragment and remove large stone volumes. Renal calyces, pelvis, and proximal ureter can be examined and stones extracted with or without prior fragmentation.

In some cases, a combination of SWL and a percutaneous technique is necessary to completely remove all stone material from a kidney. This technique, called sandwich therapy, is reserved for staghorn or other complicated stone cases. In such cases, experience has shown that the final procedure should be percutaneous nephrostolithotomy.

Open nephrostomy

Open nephrostomy has been used less and less often since the development of SWL and endoscopic and percutaneous techniques; it now constitutes less than 1% of all interventions. Disadvantages include longer hospitalization, longer convalescence, and increased requirements for blood transfusion.

Dissolution of calculi

Urinary calculi composed predominantly of calcium cannot be dissolved with current medical therapy; however, medical therapy is important in the long-term chemoprophylaxis of further calculus growth or formation.

Uric acid and cystine calculi can be dissolved with medical therapy. Patients with uric acid stones who do not require urgent surgical intervention for reasons of pain, obstruction, or infection can often have their stones dissolved with alkalization of the urine. Sodium bicarbonate can be used as the alkalizing agent, but potassium citrate is usually preferred because of the availability of slow-release tablets and the avoidance of a high sodium load.

The dosage of the alkalizing agent should be adjusted to maintain the urinary pH between 6.5 and 7.0. Urinary pH of more than 7.5 should be avoided because of the potential deposition of calcium phosphate around the uric acid calculus, which would make it undissolvable. Both uric acid and cystine calculi form in acidic environments.

Even very large uric acid calculi can be dissolved in patients who comply with therapy. Roughly 1 cm per month dissolution can be achieved. Practical ability to alkalinize the urine significantly limits the ability to dissolve cystine calculi.

Chemoprophylaxis

Prophylactic therapy might include limitation of dietary components, addition of stone-formation inhibitors or intestinal calcium binders, and, most importantly, augmentation of fluid intake. (See Dietary Measures and Prevention of Nephrolithiasis.) Besides advising patients to avoid excessive salt and protein intake and to increase fluid intake, base medical therapy for long-term chemoprophylaxis of urinary calculi on the results of a 24-hour urinalysis for chemical constituents.

Chemoprophylaxis of uric acid and cystine calculi consists primarily of long-term alkalinization of urine. If hyperuricosuria or hyperuricemia is documented in patients with pure uric acid stones (present in only a relative minority), allopurinol (300 mg qd) is recommended because it reduces uric acid excretion.

Pharmaceuticals that can bind free cystine in the urine (eg, D-penicillamine, 2-alpha-mercaptopropionyl-glycine) help reduce stone formation in cystinuria. Therapy should also include long-term urinary alkalinization and aggressive fluid intake. Captopril has been shown to be effective in some trials, although, again, strong data are lacking. Routine use should be avoided but can be added in patients who have difficulty in dissolving and preventing cystine stones.

In almost all patients in whom stones form, an increase in fluid intake and, therefore, an increase in urine output is recommended. This is likely the single most important aspect of stone prophylaxis. Patients with recurrent nephrolithiasis traditionally have been instructed to drink 8 glasses of fluid daily to maintain adequate hydration and decrease chance of urinary supersaturation with stone-forming salts. The goal is a total urine volume in 24 hours in excess of 2 liters.

The only other general dietary guidelines are to avoid excessive salt and protein intake. Moderation of calcium and oxalate intake is also reasonable, but great care must be taken not to indiscriminately instruct the patient to reduce calcium intake.

Dietary calcium should not be restricted beyond normal unless specifically indicated based on 24-hour urinalysis findings. Urinary calcium levels are normal in many patients with calcium stones. Reducing dietary calcium in these patients may actually worsen their stone disease, because more oxalate is absorbed from the GI tract in the absence of sufficient intestinal calcium to bind with it. This results in a net increase in oxalate absorption and hyperoxaluria, which tends to increase new kidney stone formation in patients with calcium oxalate calculi.

An empiric restriction of dietary calcium may also adversely affect bone mineralization and may have osteoporosis implications, especially in women. This practice should be condemned unless indicated based on a metabolic evaluation.

As a rule, dietary calcium should be restricted to 600-800 mg/d in patients with diet-responsive hypercalciuria who form calcium stones. This is roughly equivalent to a single high-calcium or dairy meal per day.

The most common causes of kidney stones are hypercalciuria, hyperuricosuria, hyperoxaluria, hypocitraturia, and low urinary volume. Each of these major factors can be measured easily with a 24-hour urine sample using one of several commercial laboratory packages now available. Kidney stone preventive therapy consists of dietary adjustments, nutritional supplements, medications, or combinations of these.

Strongly encourage patients who have a stone at a young age (ie, < 25 y), multiple recurrences, a solitary functioning kidney, or a history of prior kidney stone surgery to obtain a 24-hour urine collection for stone prevention analysis, especially if they are motivated to comply with a long-term stone prevention program. These 24-hour urine collection kits can be obtained from a number of commercial medical laboratories.

Consultation with a urologist is required when immediate ED management of renal (ureteral) colic fails. Referral to a urologist is necessary for all stones that prove refractory to outpatient management or that fail to pass spontaneously.

Consult a urologist immediately in cases of ureterolithiasis with proximal UTI. Infected hydronephrosis is a true urologic emergency and requires hospital admission, IV fluids, IV antibiotics, and immediate drainage of the infected hydronephrosis via percutaneous nephrostomy or ureteral stent placement.

Urologic consultation is also appropriate in patients with unusually large stones, high-risk medical conditions, inability to tolerate oral fluids and medications, unrelenting pain, renal failure, renal transplant, a solitary functioning kidney, or a history of prior stones that required invasive intervention.

Patients who are pregnant require a consultation with an obstetrician-gynecologist, and those with a history of severe cardiac disease or congestive heart failure may benefit from involvement of an internal medicine specialist or cardiologist.

Patients with strong motivation to prevent all future stones, those with multiple recurrences or single functioning kidneys, and all children younger than 16 years with nephrolithiasis should be referred to a specialist in nephrolithiasis prevention. A medical expert in metabolic stone prevention testing, interpretation, and prophylactic therapy is available in most communities.

Patients who do not meet admission criteria may be discharged from the ED in anticipation that the stone will pass spontaneously at home. Arrangements should be made for follow-up with a urologist in 2-3 days. Patients should be told to return immediately for fever, uncontrolled pain, or vomiting. Patients should be discharged with a urine strainer and encouraged to submit any recovered calculi to a urologist for chemical analysis.

Follow-up for patients with first-time incidence of stones should consist of stone analysis and abbreviated metabolic evaluation to rule out hyperparathyroidism, renal tubular acidosis, and chronic infection with urea-splitting bacteria.

Patients with recurrent ureterolithiasis should undergo a more thorough metabolic evaluation. Patients with recurrent stones who undergo thorough metabolic evaluation and specific therapy enjoy a remission rate in excess of 80% and can decrease the rate of stone formation by 90%. A stone chemical analysis together with serum and appropriate 24-hour urine metabolic tests can identify the etiology in more than 95% of patients.

A typical 24-hour urine determination should include urinary volume, pH, specific gravity, calcium, citrate, magnesium, oxalate, phosphate, and uric acid. Most common findings are hypercalciuria, hyperuricosuria, hyperoxaluria, hypocitraturia, and low urinary volume. Therefore, the emergency physician should encourage urologic follow-up.

Postsurgical follow-up

After surgical treatment of urinary tract calculi, the major issues include infection, ureteral obstruction, and hemorrhage. The postoperative course of minimally invasive stone-removal modalities is generally characterized by short-lived discomfort easily managed with oral medications. Continued or severe pain should prompt evaluation for complications. Repeat urine cultures and imaging studies should be performed to assess for ureteral obstruction and perforation, and the degree of circulating blood volume should be evaluated for ongoing hemorrhage.

A follow-up examination that includes abdominal radiography is often adequate after an uncomplicated stone-removal procedure. Further imaging is often unnecessary in a patient with a previous radiopaque stone who has no further symptoms. Imaging that includes assessment of renal drainage (eg, IVP, ultrasonography, CT scanning) is usually indicated in the following cases:

• Stones with unusual characteristics
• Difficult or complicated procedures
• Patients with unusual symptoms

Once postoperative complications have been excluded and the patient is clinically healthy, standard radiographic follow-up care includes abdominal radiography every 6-12 months. Radiography is often performed in conjunction with metabolic chemoprophylaxis.

Ongoing medical therapy

If a patient older than 40 years has formed a single stone that passed spontaneously or was easily treated, follow-up care for recurrent stones may be unnecessary. This patient is at a reasonably low risk for recurrence if adequate fluid intake is maintained. In other patients, whether or not they have elected directed metabolic therapy, routine follow-up care consists of plain abdominal radiography (or renal ultrasonography in the case of radiolucent stones) every 6-12 months.

If medical therapy is instituted, a 24-hour urinalysis 3 months after starting any new therapy should be performed to assess the degree of patient compliance and the adequacy of the metabolic response. Checking all possible metabolic parameters—not just the previously abnormal ones—is necessary because of the possibility of new problems arising as a result of the new therapy. Once a stable regimen has been established, annual 24-hour urinalyses are adequate.