Renal Access by Urologist or Radiologist During Percutaneous Nephrolithotomy

Introduction

P ercutaneous nephrolithotomy (PCNL) is an established technique to manage large and complex renal calculi. ¹ The 2005 American Urological Association guidelines on the management of staghorn calculi recommend PCNL as first-line treatment for renal calculi larger than 2.0 cm in diameter. ²

Access-associated complications can arise from the initial puncture (hemorrhage) and proximity of adjacent organs (lungs, pleura, colon, spleen, liver). In the United States, percutaneous access is often obtained by interventional radiologists, ³ and many urologists do not obtain their own access. ⁴ We evaluated percutaneous access for PCNL that was obtained by interventional radiologists (performed for stone treatment or collecting system decompression) or urologists and compared access outcomes and complications.

Patients and Methods

We conducted a retrospective review of 233 patients who had undergone PCNL at a single institution from July 2000 to January 2008. Patients were stratified according to percutaneous access by urologists (n = 195, group 1) or a group of interventional radiologists (n = 38, group 2). Percutaneous access was obtained by interventional radiologists a mean 25 ± 30 days before definitive stone treatment. Indications for radiologist access included obstruction and infection (33.3%), position limiting contracture (15.2%), previous genitourinary reconstruction (10.5%), solitary (7.9%) and horseshoe (2.6%) kidneys, and limited retrograde access (8.3%); 22.2% were referred from an outside hospital with nephrostomy tubes in place. Whether performed for urinary decompression or stone treatment, radiologist-acquired access was obtained without urologic consultation.

In both groups, percutaneous access was obtained using local or general anesthesia and prone positioning. In group 1, cystoscopy and ureteral catheter placement were performed at the beginning of the procedure, followed by air and/or contrast medium injection to opacify the collecting system, and access was obtained under multidirectional C-arm guidance. For patients within group 2, access was obtained under ultrasonographic and/or fluoroscopic guidance after percutaneous antegrade contrast injection. Standard access was obtained by placement of an 18- or 22-gauge access needle, depending on surgeon or radiologist preference. NephroMax™ (Boston Scientific, Natick, MA) or X-Force^® N-30 (Bard, Covington, GA) balloon dilation catheters were used for percutaneous tract dilation, followed by placement of a 30F working sheath. Site of renal entry and the number of access tracts were dependent on stone location, pelvicaliceal anatomy, and surgeon preference.

Ultrasonic and pneumatic lithotripsy, laser, and/or stone baskets or forceps were used as needed. Cases were complete when all visible stone was removed with a total operative time cutoff (including tract creation) of 240 minutes. Dependent on surgeon preference, 10 or 22F nephrostomy tubes were inserted in all patients, and 20F urethral catheters were left for a minimum of 24 hours.

CT was performed on postoperative day 1 if any residual stone burden was suspected. Stone free was defined as no residual stone fragments on postoperative imaging. Second-look nephroscopy was performed on postoperative day 2 for any residual stone burden >2 mm. In patients who did not undergo or were not stone free at the time of second-look nephroscopy, imaging (with CT or plain radiography) was obtained within 4 weeks of surgery to assess for residual stone burden. The amount and location of residual calculi dictated the necessity and type of ancillary procedures.

Preoperative, operative, and postoperative details were recorded and analyzed for each patient with regard to blood loss, outcomes, and complications. Patients were evaluated preoperatively with plain abdominal radiography and/or CT, a basic metabolic panel, complete blood cell count, coagulation studies, urinalysis, and/or urine culture. Patients with positive preoperative urine cultures (>10⁵ colony-forming units/mL) were treated with antibiotics for 3 to 14 days before their elective procedure.

Preoperative factors that were analyzed included age, sex, diabetes mellitus, hypertension, cardiac or pulmonary disease, paraplegia, coagulopathy, previous genitourinary tract reconstruction, renal ectopia, solitary kidney, hematocrit, serum creatinine level, preoperative urinary tract infection, stone size and number, presence of staghorn calculi, stone location, associated ureteral stones, and any previous procedures for active stone burden. A complete staghorn stone was defined as one that either totally filled all calices and the renal pelvis, or filled ≥ 80% of the renal collecting system. A partial staghorn was defined as one that filled the renal pelvis and at least one or more calices.

Operative factors analyzed were site of calix puncture, type and size of tract dilation, presence of preexisting nephrostomy tube, tract number, method of stone destruction, and procedure length. The postoperative factors identified were hematocrit level, serum creatinine level, need for second-look procedure, length of stay, complications, transfusion requirement, size and duration of nephrostomy tube, stone-free rate, and need for ancillary procedures.

Access difficulty between groups was compared using demographic, stone, and operative variables. In addition, both groups were compared with respect to demographics, stone type and size, complications, blood loss, transfusion requirement, stone-free rate, and ancillary procedure requirement.

Stone diameter was measured on CT scan using software available within Stentor iSite™ Enterprise imaging software (Stentor Inc,Alpharetta, GA). Stones were classified based on size, location (upper pole, midcalix/renal pelvis, lower pole), number, composition, and configuration (partial or complete staghorn). Blood loss was estimated by the largest postoperative decrease in hematocrit (measured before surgery, immediately postoperatively, and before discharge), and patients receiving blood transfusions were identified. A conservative blood transfusion strategy is used at our institution. Patients generally receive transfusion for postoperative hematocrit values less than 24%, or for hematocrit values >24% in patients with clinically significant bleeding or hemodynamic instability. Patients with intractable bleeding, hematuria, or hemodynamic instability were candidates for angiographic intervention.

Student t tests and Mann-Whitney U or Kruskal-Wallis rank sum tests were conducted to assess for differences between groups. A logistic regression multivariate analysis could not be performed because of the small number of patients in group 1. In all statistical analyses, the null hypothesis was rejected when P was <0.05. Statistical analyses were performed using SPSS version 13.0 statistical analysis software (SPSS, Chicago, IL).

Results

Of the 233 patients reviewed, 83.7% and 16.3% underwent percutaneous access by urologists or radiologists, respectively. For the overall cohort, mean patient age was 57.5 ± 16.4 years, with a male to female predominance of 54.1% to 45.9%, respectively. Mean stone diameter was 3.55 ± 1.8 cm, with 23.4% and 40.3% staghorn and partial staghorn calculi, respectively. Multiple stones were encountered in 67.5%, with stones located predominantly in the renal pelvis (75.8%), lower pole (74.9%), and upper pole (34.6%). Percutaneous access was subcostal in 62.9%, between the 11th and 12th ribs in 34.5%, and between the 10th and 11th ribs in 5.2%.

The patients and stone characteristics of the study groups are summarized in Table 1. There was no statistically significant difference between the two groups with regard to age, stone number, stone diameter, stone type, stone location, site of puncture, or body mass index. Although there was no difference in the prevalence of diabetes mellitus, pulmonary disease, or coagulopathy between groups, coronary artery disease, hypertension, and previous urinary tract infection were more common in patients who were undergoing interventional radiology access (P = 0.028, 0.023, and 0.033, respectively).

Access difficulty parameters, including staghorn calculi, multiple tracts, supracostal access, obesity, renal ectopia, previous genitourinary reconstruction, and stones within caliceal diverticulum, were comparable in patients undergoing urologist- and interventional radiologist-obtained access (Table 2). Radiologists more commonly performed access in solitary kidneys (7.9% vs 1.0%, P = 0.032), however.

Interventional radiologist-acquired access was inadequate in 36.8%, necessitating new access at the time of surgery. Among patients with unusable radiologist-obtained access, 65% and 35% were recognized as unusable preoperatively and after tract dilation, respectively. Attempted dilation of nonusable tracts did not directly result in significant complications. Radiologist access could not be used secondary to unfavorable angle for stone treatment (54.5%), nondilatable tract (18.2%), subcutaneous tunneling (9.1%), inadequate access to other calices (9.1%), nephrostomy tube placement into renal pelvis (9.1%), and posterior access that did not traverse the renal parenchyma (9.1%).

Overall, the stone-free rate was significantly greater in the urology access group on univariate analysis (99% vs 92.1%; P = 0.033). The small number of patients in the radiology-access group precluded multivariate analysis. Largest interval hematocrit decrease, transfusion requirement, complication rate, ancillary procedure requirement, median length of stay, and median time to nephrostomy tube removal were not significantly different between groups (Table 3).

Discussion

PCNL has become the treatment modality of choice for patients with large volume, complex renal stones and is the consensus first-line therapy for stones >2.0 cm in diameter. ² Historically, access to the kidney for stone treatment has been performed by interventional radiologists, ³ and many urologists in the United States do not routinely perform their own access. ⁴ Despite this trend, recent studies demonstrate that percutaneous access can be performed safely and effectively by urologists. ^{3,5 –8}

Watterson and associates ⁸ retrospectively compared percutaneous access performed by radiologists and urologists with regard to access-related complications, bleeding, failure to access, pneumothorax, other organ injury, and stone-free rates. Access-related complications and stone-free rates were significantly worse in the radiology access group (27.7% vs 8.3%, P < 0.05), and they reasoned that this disparity resulted from radiologists' lack of familiarity with the intricacies of stone removal or placement of multiple tracts for large stone burdens. ⁸ Conversely, El-Assmy and colleagues ⁵ found no differences in complications and stone-free rates when comparing the results obtained by radiologists and urologists. Finally, Lashley and Fuchs ³ reported 522 cases of urologist-acquired renal access and found complication and failure rates compared favorably with reports of radiologist-acquired renal access.

In many centers, renal access is acquired in the operating room by an interventional radiologist at the time of definitive stone treatment, as is the case in the aforementioned studies. ^5,8 The use of radiologist-obtained access has been driven in part by hospital established systems for radiologists to gain access and favorable physician reimbursement given to interventional radiologists who perform distinct procedures. ⁹ Urologists receive lower reimbursement for percutaneous access that is obtained at the time of stone treatment than radiologists performing the procedure on the same day because of the Medicare policy that reimburses the second of two distinct procedures at 50% of allowable. ⁹

Our series is uniquely different in that radiologist-obtained access was performed independent of urologic intervention, including a subcohort of patients who were referred with access gained before transfer of care. This may contribute to the improved stone-free rate in the urology access group and to the large percentage of patients (37%) in whom radiologist-acquired access was unusuable at the time of urologic intervention. Some patients in the radiology cohort were referred for preprocedure access because of challenging anatomy, solitary renal unit, or for urosepsis necessitating acute percutaneous decompression.

The comparison performed in our cohort may be inherently biased against radiologists, in that a number of patients underwent access by a radiologist for acute urinary decompression, which may yield different results than access performed for stone treatment. In a system in which radiologists and urologists do not work in conjunction to obtain renal access before PCNL, however, poor communication may lead to unusable access, and patients may be subjected to the increased risk of additional access attempts.

Evaluation of access difficulty revealed that more solitary kidneys were accessed by radiologists (7.9% vs 1.0%, P = 0.032). In addition, there was an increased prevalence of hypertension, coronary artery disease, and previous urinary tract infection among patients in the radiology-access group. The groups were otherwise comparable. While medical comorbidities may predispose patients to surgical complications, further subanalysis of patients with solitary kidneys, hypertension, coronary artery disease, or previous urinary tract infection revealed no difference in stone-free rates or access-related complications.

Overall stone-free rates were significantly higher in the urology-access group (99.0% vs 92.1%, P = 0.033), despite similar patient and stone complexity. Urologists' familiarity with the subsequent steps necessary for stone removal may improve access placement and explain the improved stone-free rate. Multiple access tracts used for multiple or large stones in the urology cohort in 5.2% compared with 0% in the radiology cohort could also account for the improved stone-free rate. The need for placement of additional percutaneous access at the time of surgery in patients with unusable radiologist-obtained access shortens the time available for stone fragmentation and removal, and could also account for the observed difference in overall stone-free rate.

Although generally safe, PCNL is associated with significant perioperative morbidity, ¹⁰ including minor complications, such as urinary extravasation (7.2%), ¹¹ transfusion (11.2%–17.5%), ^{11 –13} and fever (21.0%–32.2%), ^11,14,15 whereas major complications, such as sepsis (0.3%–4.7%), ^11,13,14,16 colonic (0.2%–0.8%), ^1,11,17,18 or pleural injury (0.0%–3.1%) ^11,16 are rare. Our overall major and minor complication rates were 7.7% and 17.6%, respectively, which is within the reported range (3%–18%) ^1,11,19 of complication rates during PCNL. Within our cohort, there was no difference in access-related complications between groups, which confirms the safety of urologist-obtained renal access during PCNL.

Blood loss is common during PCNL and frequently occurs from the nephrostomy tract itself, but it can also be secondary to parenchymal lacerations that are incurred during tract dilation or stone breakup, or lesions of the vascular system arising from pseudoaneurysms or arteriovenous fistulae. ¹⁰ Blood loss can occur intraoperatively or postoperatively with varying severity, depending on etiology. Blood transfusion rates after percutaneous renal access have been reported from 5% to 18%, with 0.3% to 3.0% necessitating angiographic intervention. ^{1,13,16,20 –22}

In our cohort, rates of blood transfusion were comparable in patients who were undergoing percutaneous access by urologists and radiologists (1.0% vs 2.6%, respectively; P = 0.415). Mean interval hematocrit decrease, a surrogate for blood loss, was also similar between groups. Although the risk of blood transfusion after PCNL is influenced by many factors, including staghorn calculi, ²³ large stone burden, ²² diabetes mellitus, ^20,21 and multiple access tracts, ^20,21,24 the type of puncture by urologist or radiologist was not a risk factor for bleeding in the final model.

Our study has several limitations. The retrospective nature of our study imparts a significant selection bias, especially within the interventional radiology cohort. Patients who are undergoing percutaneous access for emergent decompression of an infected and obstructed system are clearly different from patients who are undergoing nephrostomy tube placement in preparation for PCNL. The former, however, represents a small portion of the radiology cohort, and on subset analysis, those patients had no difference in complications or stone-free rate compared with the remaining cohort. All patients undergoing emergent nephrostomy tube placement needed additional access placement by the urologist at the time of PCNL, which partly explains the high rate of unusable radiology access (36.8%) observed in our cohort. Patients undergoing emergent decompressive nephrostomy tube placement should be counseled regarding the relatively high likelihood of needing additional access at the time of definitive stone treatment, and proper arrangements should be made to ensure that proper personnel and equipment are available. In addition, although we attempted to match access difficulty, demographics, and stone characteristics between groups, our study was not designed prospectively, and there were minor differences between groups.

Conclusion

Despite the limitations of the study, our results support the safety and efficacy of urologist-acquired percutaneous renal access for PCNL. Although outcomes were acceptable in patients who had undergone either urologist- or radiologist-acquired access, they would likely improve with improved communication between departments. We encourage urologists to effectively communicate with interventional radiologists before percutaneous renal access.