NEPHROLITHIASIS

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The evaluation and treatment of patients with nephrolithiasis is rapidly changing. New imaging modalities have emerged that have changed the way we evaluate patients with flank pain. Criteria previously used as indication for admission no longer apply, and many of these same patients are now managed as outpatients. This chapter will review the subject of nephrolithiasis as it pertains to emergency medicine physicians. When applicable, evidence-based medicine reviews of certain articles are included.

Section snippets

EPIDEMIOLOGY

Approximately 3%–5% of the population will experience nephrolithiasis during their lifetime. Depending on the type of stone, up to 50% of these patients will have a recurrence within 10 years.19 Although several of the disorders that cause nephrolithiasis are hereditary (familial renal tubular acidosis, cystinuria), there has been no conclusive data to date that nephrolithiasis is hereditary. The incidence of stone disease is highest among whites, reportedly twice as high as that of Asians. It

PATHOPHYSIOLOGY BEHIND STONE FORMATION

Stone formation occurs because of supersaturation of the urine with oxalate and calcium. As the amount of solute put into solution is increased, the solution goes through stages of saturation. When the amount of solute is below the thermodynamic solubility product, it dissolves into the solution (undersaturated). At some point, the addition of more solute will not dissolve into solution (saturated). After this point, the addition of more solute causes crystals to precipitate out of solution (

CLINICAL PRESENTATION

Patients with urolithiasis most commonly present to the emergency department (ED) with renal colic. They may also present secondary to infection or complications associated with the treatment of nephrolithiasis.

Renal colic presents abruptly as a severe paroxysmal pain on the affected side. It usually does not resolve completely before the next wave of pain begins. This visceral type pain, caused by the distention of the ureter, is secondary to obstruction of the ureter or passage of the stone

HISTORY

The history obtained from the patient with suspected renal colic can be divided into three realms. First, risk factors for the formation of stones should be elicited. These include previous episodes of renal colic, presence of previously asymptomatic renal calyx stone, as well as a family or personal history of any hereditary disorder that can cause nephrolithiasis (familial renal tubular acidosis, cystinuria, and idiopathic hypercalciuria). A history of recurrent or chronic UTIs may put the

PHYSICAL EXAMINATION

The physical examination of the patient with suspected renal colic confirm the diagnosis and rule out other conditions that mimic renal colic. Starting with the vital signs, the patient frequently has an adrenergic surge associated with pain, including tachycardia, hypertension (relative to the patient's usual blood pressure), tachypnea, and diaphoresis. The presence of fever is usually not associated with this response and should suggest infection, an important finding since an obstructed,

DIFFERENTIAL DIAGNOSES

Although the differential diagnoses for patients presenting with symptoms consistent with renal colic are listed in List 1, some deserve special mention. It is essential that the physician rule out the presence of the potentially life-threatening diseases.

List 1. Differential Diagnoses

  • Abdominal aortic aneurysm

  • Renal artery thrombosis/Embolism/Dissection

  • Appendicitis

  • Pyelonephritis

  • Ectopic pregnancy

  • Ovarian torsion

  • Diverticulitis

  • Musculoskeletal pain

  • Peritonitis

  • Ischemic bowel

  • Acute

EVALUATION

Evaluation of a patient with nephrolithiasis in the ED can be divided into laboratory and imaging studies.

LABORATORY STUDIES

Laboratory studies that should be considered include urinalysis, urine culture, pregnancy test, complete blood count with differential, electrolytes, blood urea nitrogen (BUN), and creatinine. All women of reproductive age should undergo a urine pregnancy test.

The urinalysis reveals hematuria in 90% of patients with stones. However, approximately 10% of patients with renal colic do not have hematuria. As well, false positives on the dipstick occur secondary to myoglobin or povidone-iodine.

TO STUDY OR NOT TO STUDY

When faced with the patient who has symptoms consistent with acute renal colic, the physician must decide if the patient needs emergent imaging. Unfortunately, there is little consensus regarding which patients with renal colic need imaging, or whether they need it before leaving the ED. Some clinicians image only those patients presenting with an apparent first time stone. Others image all patients presenting with probable renal colic even if they have a history of stones. All patients with

IMAGING MODALITIES

Which imaging modality is best depends both on its accuracy in identifying ureteral stones and the presence of obstruction, as well as on its ability to identify disease that mimic renal colic. If renal infarction is included in the differential diagnosis, it is important that the imaging modality assess the functional status of the kidneys. Additionally, consideration must be given to the side effects of the tests. Five radiographic modalities can be used to evaluate patients with renal colic:

PLAIN ABDOMINAL RADIOGRAPHS

Many texts and articles tout the plain radiograph as being able to detect 90% of all renal stones.36 This practice was challenged in a 1985 study whose results showed a sensitivity of 62% and a specificity of 67%.29 Aside from its lack of accuracy in diagnosing renal stones, the plain film provides little information about other sources of flank pain and no information about the functional status of the kidney.22 If the clinician plans to advance to another study, the utility of a KUB is even

ULTRASOUND

A 1988 study prospectively evaluated 85 patients with the suspected diagnosis of renal colic with both ultrasound and IVP. Both the ultrasound and IVP identified calculi in 44 patients (sensitivity of 64% and specificity of 100%). Ultrasound indirectly identified another 21% and IVP another 26%, by detecting hydronephrosis alone (respective sensitivities of 85% and 90%, specificities of 100% and 94%). This study suggests that ultrasound in experienced hands is as effective as IVP in diagnosing

IVP

In the discussion of ultrasound versus the gold standard of IVP, the clinician must remember three pearls. Stones are irregularly shaped, often causing incomplete obstruction without hydronephrosis. Administration of contrast causes a brisk diuresis, which may accentuate the degree of dilation. Most importantly, the IVP evaluates renal function.

The IVP has long been considered the gold standard in evaluating for urolithiasis. However, the helical CT in many institutions has recently supplanted

MRI

The new modality of MRI urography was evaluated for the assessment of ureteric obstruction in a recent study (Fig. 3). With the HASTE MRI urography, all 41 cases of acute and chronic obstruction were noted. The MRI was able to determine chronic versus acute obstruction by signals read as perirenal fluid surrounding 20 of the 23 acutely obstructed kidneys.25 MRI is difficult to use in the ED setting for all the usual reasons (cost, access, presence of magnetically active implants, and patient

HELICAL CT SCANS

The advent of noncontrast helical CT scanning has added a new diagnostic modality to the evaluation of renal stones. A small 1995 study (20 patients) compared noncontrast helical CT to IVP in the evaluation of acute flank pain. Of the 20 patients, 12 were shown to have obstruction. All 12 were identified by both IVP and noncontrast helical CT. The CT showed a stone as the presumptive cause of obstruction in 11, whereas the IVP identified the stone in only five patients. Also, CT-diagnosed

Hydration

Patients who have clinical dehydration secondary to vomiting and decreased oral intake should receive intravenous fluid hydration. The idea that aggressively hydrating the patient will cause a “pressure head” that would help the stone migrate down the ureter is debatable. Previously mentioned studies show that glomerular filtration rate for the obstructed kidney decreases. As well, overly aggressive hydration may dilute the IVP contrast and produce a less than optimal study. Conversely, giving

ADMISSION

Admission criteria vary from institution to institution (List 2). Regional variations should be learned. However, there are some frequently quoted absolute and relative indications for admission.

List 2. Admission Criteria

Absolute Indications

  1. Intractable vomiting

  2. Intractable pain

  3. Single kidney or transplanted kidney with obstruction

  4. Concomitant urinary tract infection with obstruction

  5. Hypercalcemic crisis

Relative Indications
  1. Fever

  2. Stone larger than 6 mm

  3. Solitary kidney

  4. Kidney transplantation

  5. High grade obstruction

CONSULTATION

The urologic consultant is available to the emergency medicine physician for three issues: admission, request for consultation on patients with relative indications for admission, and clarification of care on a complicated case. The goal of this monograph is to clarify the care of a majority of patients with renal colic.

OUTPATIENT CARE

Patients should be discharged with a combination of an NSAID and a narcotic analgesic. They should be encouraged to maintain adequate hydration to maintain clear urine. Patients should strain their urine until the stone passes. They should return for medical evaluation for a fever of greater than 100.4 F, uncontrollable pain or vomiting, or if they develop abdominal pain and tenderness. If they pass the stone, they should bring it in for analysis if the etiology of their stones has not been

Obstruction

Does the presence of obstruction cause any change in the treatment or disposition of a patient with renal colic? If obstruction occurs in the presence of an infection, the obstruction must be relieved emergentlypossible. However, if obstruction occurs in the absence of infection, how long does it take for irreversible damage to occur?

Decreases in renal blood flow as well as in ureteral pressures in the obstructed kidney begin 5–18 hours after obstruction. The degree of the reversibility of this

Pregnancy Issues

The evaluation for a possible kidney stone in a pregnant patient arises in two unique problems: the dose of radiation to the fetus and the normal physiologic dilation of the ureters.35 Ionizing irradiation of the fetus may increase the risk of teratogenicity, childhood cancer, or mental retardation. For these reasons, the dose of ionizing radiation should be minimized in pregnant women, especially those at less than 16 weeks gestation.

The upper urinary tract begins to dilate in the first

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