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considered necessary because the precipitation of uric acid is unlikely at a higher urine pH. A distinctive feature of uric acid stones is their radiolucency- Impaction along the genitourinary tract is a serious complication of renal calculi and can cause several physiologic changes.Surgical intervention can be performed on an outpatient basis, provided the patient is able to tolerate oral intake and has adequate pain control unless the stone is infected, renal damage is considerable, there are bilateral obstructing stones, or there is obstruction of a solitary or transplanted kidney.Once obstruction occurs, a rapid redistribution of renal blood flow results in a decrease in the glomerular filtration rate (GFR).Subsequent infectious complications include pyelonephritis, perinephric abscess, and gram-negative bacterial sepsis.As glomerular and tubular function decrease, renal excretion shifts to the unaffected kidney.The stone behaves as a foreign body and leads to stasis and obstruction, decreasing host resistance and increasing the incidence of infection.Up to 95% of stones larger than 8 mm become impacted along the genitourinary tract, and lithotripsy or surgical removal is usually required.Obstruction also causes a rapid decrease in ureteral peristaltic activity. 85.4).

considered necessary because the precipitation of uric acid is unlikely at a higher urine pH. A distinctive feature of uric acid stones is their radiolucency-
Impaction along the genitourinary tract is a serious complication of renal calculi and can cause several physiologic changes. Once obstruction occurs, a rapid redistribution of renal blood flow results in a decrease in the glomerular filtration rate (GFR). As glomerular and tubular function decrease, renal excretion shifts to the unaffected kidney. Obstruction also causes a rapid decrease in ureteral peristaltic activity. In the presence of infection, renal and ureteral function may be impaired. Complete obstruction of the ureters may lead to loss of renal function with an increased incidence of irreversible damage after 1 to 2 weeks. Partial obstruction is associated with a lower likelihood of renal injury but may still result in irreversible damage.
Although calculus size and location are important determinants of the degree of discase, the major cause of progressive renal damage Is associated infection. The stone behaves as a foreign body and leads to stasis and obstruction, decreasing host resistance and increasing the incidence of infection. Subsequent infectious complications include pyelonephritis, perinephric abscess, and gram-negative bacterial sepsis.
The three primary predictors of stone passage without the need for surgical intervention are calculus size, location, and degree of patient pain. The most important factor that relates to passage of a calculus though the genitourinary tract is its size. Approximately 90% of stones smaller than 5 mm pass spontancously within 4 weeks. This percentage decreases to 15% for stones 5 to 8 mm in size. Up to 95% of stones larger than 8 mm become impacted along the genitourinary tract, and lithotripsy or surgical removal is usually required. Surgical intervention can be performed on an outpatient basis, provided the patient is able to tolerate oral intake and has adequate pain control unless the stone is infected, renal damage is considerable, there are bilateral obstructing stones, or there is obstruction of a solitary or transplanted kidney. Spontaneous passage is more frequent with stones located below the midureter than those located above the midureter.
Renal calculi seldom cause complete obstruction. There are five sites along the ureter at which calculi are likely to become impacted (Fig. 85.4). First, a stone may lodge in the calyx of the kidney or