Struvite and Staghorn Calculi Workup
- Author: Maxwell Meng, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS more...
Prior to treatment of struvite stones, complete serum laboratory studies are required, including the following:
Complete blood cell count
Prothrombin and activated partial thromboplastin times
Serum electrolyte evaluations
Chronic anemia may necessitate preoperative blood typing and screening for potential blood transfusion, especially if open or percutaneous surgery is planned.
More importantly, urinalysis and urine culture should be performed several days before surgery, and specific antibiotic therapy should be initiated at least 24 hours prior to treatment. Findings from cultures of voided urine may not accurately reflect renal microbiology, with a negative culture finding or discrepant organisms.
Additional aspects of the metabolic evaluation of urinary stones should be pursued because up to 50% of patients with infection-related stones have concomitant metabolic abnormalities. Thus, a 24-hour urinary collection (for calcium, oxalate, uric acid, citrate, phosphate, uric acid, magnesium, sodium, total volume, and pH) and simultaneous serum tests for calcium, uric acid, electrolytes, and phosphate are indicated. If the serum calcium level is elevated, it should be rechecked along with serum parathyroid hormone levels.
If the patient has undergone prior stone removal surgery, information regarding the chemical composition of any previous stones is extremely important.
Plain abdominal radiography usually documents the extent of struvite staghorn calculi; however, additional imaging tests that reveal the anatomy of the renal collecting system can be helpful.
Intravenous urography can clearly delineate the pelvic calyceal anatomy. Currently, however, noncontrast CT scanning followed by intravenous contrast CT scanning is obtained most often in the evaluation of urinary stones. CT scans also display the adjacent structures and may aid in selecting the safest percutaneous tract to access the renal collecting system.
Narrow, scarred infundibula indicate the need for percutaneous nephrostomy (PCN), while wide, large renal infundibula suggest that extracorporeal shockwave lithotripsy (SWL) might be adequate. If the passageway between the calyces and renal pelvis is open and unrestricted, stone fragments produced during SWL are much more likely to pass.
Traditionally, staghorn calculi were defined as partial if the renal pelvic stone extended into at least 2 calyceal groups or complete if at least 80% of the collecting system was filled. Some experts argue that, to compare published stone-free rates, especially in the era of minimally invasive modalities, an improved classification system based on stone size should be implemented.
CT scanning with 3-dimensional reconstruction offers accurate stone volumes, but the added radiographic analysis is costly, time consuming, and neither practical nor readily available. Lam and associates reported a simple 2-dimensional electronic computerized tracing technique that calculated stone surface area, which correlated well with stone volume.
Performing nuclear renography is not necessary, but the findings are helpful for determining the relative function of the affected kidney. If the kidney has minimal function, nephrectomy may be needed. However, overall and relative renal function must be considered prior to removal of the kidney.
Dual energy CT with advanced postacquisition processing has shown some promise in preoperative determination of stone composition. In a small sample of patients, Zilberman et al demonstrated that all struvite stones have a measured attenuation of 900 Hounsfield Units (HU) or less. This type of work was reproduced in both human models and another small population of test subjects. Accurate preoperative prediction of stone composition may assist with planning for perioperative antibiotic and surgical management.
Ultrasonography alone is insufficient, but images show coexisting hydronephrosis. MRI does not help visualize urinary calculi; therefore, this modality has no role in preoperative and postoperative imaging of struvite stones.
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|Generic name||Citric Acid, glucono-delta-lactone, and magnesium carbonate|
|Description||Action on susceptible apatite calculi results from exchange of magnesium from irrigating solution for insoluble calcium contained in stone matrix or calcification. Magnesium salts thereby formed are soluble in gluconocitrate irrigating solution, resulting in dissolution of calculus. Struvite calculi are composed mainly of magnesium ammonium phosphates, which are solubilized by hemiacidrin due to acidic pH. Essential that patients be free from urinary tract infections prior to initiating chemolytic therapy. Used for local irrigation dissolution of renal calculi composed of apatite (a calcium carbonate-phosphate compound) or struvite (magnesium ammonium phosphates) in patients who are not candidates for surgical removal of calculi. Also used as adjunctive therapy to dissolve residual apatite or struvite calculi and fragments after surgery or to achieve partial dissolution of renal calculi to facilitate surgical removal.|
|Adult Dose||Renal calculi:
Place nephrostomy tube at surgery or percutaneously to permit lavage of calculi; single catheter may be sufficient if calculus not obstructing ureter or ureteropelvic junction; in patients with obstructed ureter, a retrograde catheter can be placed through ureter to renal pelvis via a cystoscope (used to irrigate calculus while percutaneous nephrostomy tube used for drainage)
Pressure measurements are made under fluoroscopic guidance to ensure 2-3 mL/min can be infused without causing pain, pyelovenous or pyelotubular backflow, or manometric evidence of elevated pressure within collecting system
Irrigation should not be started before fourth or fifth postoperative day; irrigation of renal pelvis is begun with sterile saline only after sterile urine demonstrated
Saline is infused at rate of 60 mL/h initially, and rate is increased until pain or an elevated pressure (25 cm water) appears or until maximum flow rate of 120 mL/h achieved; inspect site of insertion for leakage; if leakage occurs, irrigation is discontinued temporarily to allow for complete healing around nephrostomy tube; if no leakage or flank pain occurs, start irrigation with flow rate equal to maximum rate achieved with saline solution
Place clamp on inflow tube and instruct patients and nursing personnel to stop irrigating solution whenever pain develops; nursing personnel responsible for performing irrigation must be instructed concerning location of nephrostomy tube(s) and direction of flow of irrigating solution to ensure against misconnection of inflow and egress tubes
Perform nephrotomography periodically to assure proper placement of catheter tip and to assess efficacy; if stones fail to change size after several days of adequate irrigation, discontinue procedure; upon demonstration of complete dissolution of calculus, inflow tube is clamped and left in place for few days to ensure that no obstruction exists, after which time nephrostomy tube should be removed
Instill 30 mL through urinary catheter into bladder; clamp catheter for 30-60 min and release clamp to drain; repeat 4-6 times/d; continuous drip through 3-way Foley catheter is alternative means of dissolving bladder stones; in presence of bladder spasm and associated high pressure reflux, all precautions required for irrigation of renal pelvis must be observed
|Pediatric Dose||Not established|
|Contraindications||Urinary tract infections; presence of demonstrable urinary tract extravasation; ureteral catheters, nephrostomy or pyelostomy tubes, or renal lavage for dissolving calculi|
|Interactions||May increase toxicity of magnesium-containing medications|
|Pregnancy||C - Safety for use during pregnancy has not been established.|
|Precautions||Fever, urinary tract infection, signs and symptoms consistent with urinary tract infection, persistent flank pain, or if hypermagnesemia or elevated serum creatinine level develops (urea-splitting bacteria reside within struvite and apatite stones and serve as source of infection); dissolution therapy in presence of infected urinary tract may lead to sepsis and death; severe hypermagnesemia has occurred
Caution when irrigating renal pelvis of patients with impaired renal function; severe hypermagnesemia may result in hyporeflexia, dyspnea, apnea, coma, cardiac arrest, and subsequent death; treatment should include discontinuation of therapy followed by treatment with IV calcium gluconate, fluids, and diuresis in severe cases
|Generic name||Suby solution G|
|Brand names||Suby solution G|
|Description||Used to dissolve phosphatic calculi or incrustations in the bladder and urethra.|
|Adult Dose||1-3 L qd by intermittent irrigation or by tidal instillation and drainage to allow continuous irrigation of bladder for periods of several hours; intermittent irrigation of bladder (after manner of intermittent peritoneal dialysis) may be preferred to promote longer contact of irrigant with bladder stones; tidal (continuous inflow and outflow) irrigation may be less efficient and require larger amounts of irrigation fluid|
|Pediatric Dose||Administer as in adults|
|Contraindications||Bladder infections, bleeding, ulcerations, or other open wounds; IV/IM/SC injections|
|Pregnancy||C - Safety for use during pregnancy has not been established.|
|Precautions||For use only in irrigation of lower urinary tract; not for dissolving phosphate calculi in renal pelvis (may cause back pressure that could reactivate existing pyelonephritis); repeated or continuous use may cause bleeding (irritating to urethra; after each treatment, irrigate with sterile saline or water); 4 cases of sudden death reported during lavage therapy with similarly acting solution; not to be used in place of other indicated measures, including correction of underlying metabolic disorders, surgical intervention, and treatment of infection|
|Generic name||Acetohydroxamic acid|
|Description||Reversibly inhibits bacterial enzyme urease, thereby inhibiting hydrolysis of urea and production of ammonia in urine infected with urea-splitting organisms. Reduced ammonia levels and decreased pH enhance effectiveness of antimicrobial agents and increase cure rate of these infections. Does not acidify urine directly, nor does it have direct antibacterial effect. In patients with urea-splitting urinary infections (often accompanied by struvite stone disease) that are recalcitrant to other management, reduces pathologically elevated urinary ammonia and pH levels.|
|Adult Dose||12 mg/kg/d PO tid/qid on empty stomach recommended initially; not to exceed 1.5 g/d|
|Pediatric Dose||10 mg/kg/d PO initially; monitor clinical condition and hematologic status; dosage titration may be required|
|Contraindications||Patients whose physical state and disease are amenable to surgery or antimicrobial agents, urine is infected by non–urease-producing organisms, or renal function is poor (eg, serum creatinine >2.5 mg/dL or CrCl < 20 mL/min) and females without satisfactory method of contraception whose urinary infections can be controlled by culture-specific oral antimicrobial agents|
|Interactions||Absorption of iron and AHA may be reduced from intestinal lumen when both drugs taken concomitantly (give iron IV when indicated)|
|Pregnancy||X - Contraindicated in pregnancy|
|Precautions||Bone marrow depression (ie, leukopenia, anemia, thrombocytopenia) has occurred in animals receiving large doses (never reported in humans); hemolysis with decrease in circulating red blood cells, hemoglobin levels, and hematocrit values also noted; in renal impairment, closely monitor patients and reduce daily dose to avoid excessive drug accumulation|