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Comparative study of percutaneous tic technique versus standard percutaneous nephrolithotomy
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Comparative study of percutaneous tic technique versus standard percutaneous nephrolithotomy Naveen Krishnan MD MS , Tim Large MD , Crystal Valadon BS , Amy Krambeck MD PII: DOI: Reference:
S0090-4295(20)30174-6 https://doi.org/10.1016/j.urology.2019.12.040 URL 21985
To appear in:
Urology
Received date: Revised date: Accepted date:
6 August 2019 4 December 2019 11 December 2019
Please cite this article as: Naveen Krishnan MD MS , Tim Large MD , Crystal Valadon BS , Amy Krambeck MD , Comparative study of percutaneous tic technique versus standard percutaneous nephrolithotomy, Urology (2020), doi: https://doi.org/10.1016/j.urology.2019.12.040
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Comparative study of percutaneous tic technique versus standard percutaneous nephrolithotomy
Naveen Krishnan, MD MS1, Tim Large, MD1, Crystal Valadon, BS2, Amy Krambeck, MD1 From Indiana University Department of Urology1 and Louisville School of Medicine2
Dr. Amy Krambeck is a consultant for Boston Scientific Corporation, Lumenis and Cook Medical
Corresponding Author: Amy E. Krambeck, MD Michael O. Koch Professor of Urology Indiana University/IU Health Physicians, 1801 Senate Blvd Suite 220, Indianapolis, IN 46212 Phone: 317-962-3700; Email: [email protected] Krishnan: [email protected]; Large: [email protected]; Valadon: [email protected]
Keywords: percutaneous nephrolithotomy, PCNL, renal access
Acknowledgements: None Financial Disclosures: None
There is no conflict of interest for any of the authors. There are no colored figures for this manuscript.
ABSTRACT Objective: To compare the PERC-tic technique, described as placement of dual wires under fluoroscopic guidance adjacent to the stone within the obstructed calyx, to standard percutaneous nephrolithotomy (PCNL) with working wires secured down the ureter. Materials and Methods: This is a retrospective cohort study of patients who underwent a PCNL procedure between October 2016 and November 2018. Patients undergoing the perc-tic technique were compared to patients undergoing standard PCNL. Regression models evaluated if PERC-tic PCNL was associated with equivalent stone-free rates to standard PCNL at 90 days, need for secondary procedures, and 90-day hospital readmission. Results: This study involved 126 PCNL cases of which 63 were done using the PERC-tic technique and 63 with standard PCNL. In multivariate analysis, there was no statistical difference in 90-day stone-free rate between standard PCNL and PERC-tic cohorts (p=0.08). We did note a 6 times higher likelihood of needing secondary procedures for residual stones in the PERC-tic versus standard PCNL groups (71% vs 30% p< 0.0001). There was no statistical significance in 90-day hospital readmission rates between groups (p=0.47). Conclusions: Our findings suggest similar stone free rate at 90 days and higher rates of secondary procedures after PERC-tic PCNL compared to the standard approach; however, there was no difference in complications. These findings may reflect decreased visualization with the PERC-tic technique or simply be reflective of the case difficulty requiring the use of the PERCtic technique. These findings can be used for patient counseling when considering this technique for complex stone disease.
INTRODUCTION Since first described by Fernstrom and colleagues in 1976, percutaneous nephrolithotomy (PCNL) has progressed into the surgical standard of care for the treatment of patients with large complex stone burdens 1-3. Notable improvements in both equipment and technique, including advancements in diagnostic imaging, reduction in the size and complexity of percutaneous surgical equipment, and novel ways to safely access the collecting system, are at the cornerstone of the PCNL evolution 2–5. These changes strive to reduce surgical morbidity while improving stone clearance rates. Due to its safety and efficacy, both American and European guideline panels recommend PCNL as the primary surgical intervention for complex stones greater than two centimeters 6 7. Establishing percutaneous access optimally occurs over a stiff wire extending through the calyx of entry down the ureter and terminating within the bladder. At times, anterograde advancement of a wire down the ureter is unsafe or not feasible. Examples where ureteral cannulation is less likely include cases involving a ureteropelvic junction (UPJ) obstruction, a target stone that lies within a diverticulum or obstructs the calyx or infundibulum of entry. The percutaneous diverticulum (PERC-tic) technique obviates the need for ureteral cannulation by coiling a working and safety wire in the punctured calyx, renal pelvis, or diverticulum prior to dilating the tract for placement of the percutaneous access sheath. This technique has been described in the treatment of caliceal diverticulum calculi, but has not been previously described for patients with other anomalies restricting antegrade ureteral access 8,9. Our study examines the use of the PERC-tic technique versus standard PCNL (where a working wire has successfully been positioned down the length of the ureter). In cases where PERC-tic technique is used, there is the perception that the renal unit is more mobile during the
balloon dilation and percutaneous access sheath advancement., In addition to the inherent challenges of treating stones that require the PERC-tic PCNL, visualization can be perceived as decreased secondary to bleeding after advancement of the access sheath into the mobile kidney The perceived increase in intraoperative bleeding during PERC-tic PCNL is insufficient enough to warrant transfusion but is felt to affect intraoperative vision. We, therefore, hypothesize that PERC-tic PCNL is safe but results in greater need for secondary endourologic procedures to render patients stone free.
MATERIALS AND METHODS Study population We conducted a retrospective cohort study of PCNL procedures completed between October 2016 to November 2018 based on our prospectively collected tertiary care institutional database. We considered each case with respect to number of renal units. We excluded any patients with significant anatomic anomalies including spinal deformity, horseshoe kidney, pelvic kidney, or renal transplantation. Surgical Technique All patients in this study were originally scheduled to undergo standard PCNL in the prone position. After it was determined that anterograde ureteral access intraoperatively could not be established, the PERC-tic technique was used. For patients undergoing standard PCNL, we would place an Amplatz Super Stiff™ guide wire down the ureter. We would then place an additional safety wire which was either a hybrid Sensor® polytetrafluoroethylene-nitinol guide wire with hydrophilic tip or a 0.038 Fr BARD® straight movable core guidewire. The tract was then dilated to 30 Fr and an access sheath was placed (Supplementary image 1).
For patients undergoing PERC-tic technique, anterograde ureteral access could not be established despite multiple attempts. Therefore, we would first coil a ZIPwire™ hydrophilic guide wire from Boston Scientific within the renal pelvis or obstructed calyx. We then used a ureteral catheter to replace this wire with a 0.038 Fr BARD® J movable core guidewire. We would then coil an additional J movable core guidewire as well using an 3mm Brite Tip TM interventional sheath from Cordis. We would ensure that there was an abundant amount of coiled wire to prevent tract dilation over the insubstantial portion of the wire. The tract was then dilated to 30 Fr using the BARD X-Force® N30 nephrostomy dilation catheter set. Once the stone burden was sufficiently removed, we always established anterograde access down the ureter using a wire to help stabilize the renal unit. All patients within both groups included only a single access for each kidney. None of the PERC-tic patients had standard access. Outcomes The primary outcome was stone-free rate (SFR) at 90 days follow up appointment as assessed by radiologic imaging [computerized tomography (CT), abdominal plain x-ray, or renal ultrasound]. All patients in this study had a CT of the abdomen and pelvis without contrast on post operative day one. If there were any residual fragments greater than two mm remaining, the patient was then taken for a secondary procedure either ureteroscopy or PCNL using the established tract. The secondary procedure occurred on post operative day two. The secondary outcomes in this study include rate of secondary procedure and rate of 90-day hospital readmission. Patients who were returning for a secondary endourologic procedure did not count as a hospital readmission. We controlled for patient demographic and stone factors including age, skin-to-stone distance, body mass index (BMI), Guy’s stone score 10, need for an 18 French
(Fr) Malecot nephrostomy tube post operatively, and renal bleeding. All Guy’s stone score 4 were staghorn stones. Our standard protocol is to leave a 10 Fr nephrostomy tube after PCNL; however, if there is significant intraoperative bleeding obscuring visualization we will leave an 18 Fr Malecot nephrostomy tube. The 18 Fr Malecot nephrostomy tube allows direct access to the ureter and maximizes urinary drainage. Renal bleeding was characterized as presence, on the postoperative day one CT scan, of a perinephric hematoma, an intra renal bleed or both. All patients were followed within 90 days with a CT of the abdomen and pelvis without contrast to assess stone free rate. All clinical data and imaging were independently reviewed by two urologists.
Statistical analyses We conducted a bivariate analyses to examine demographic and clinical factors among patients after undergoing standard versus PERC-tic PCNL. Specific variables of interest included, but were not limited to: age, gender, body mass index (BMI), change in hemoglobin between the pre operative and post operative day one setting, stone size and location, skin-tostone distance, and postoperative nephrostomy tube drainage. Additionally, stone complexity was graded using the Guy’s stone score, and any evidence of bleeding was assessed based on presence of a renal bleed on the postoperative CT. We used Student’s t-statistic and CochranMantel-Haenszel chi-square tests when appropriate. Second, we performed multivariable logistic regression analyses adjusting for the following variables: age, use of PERC-tic technique, skin-to-stone distance, Guy’s stone score of four, and change in hemoglobin. A logistic regression model with bias-corrected 95% confidence
intervals (CIs) was generated. The referent groups were always male patients, standard PCNL patients and Guy’s stone score of three, two, or one. Lastly, we examined the different methods of postoperative renal drainage between standard PCNL and PERC-tic patients. The different methods include a five or six Fr ureteral catheter, a 10-Fr nephrostomy catheter with or without a ureteral catheter, or an 18-Fr Malecot catheter. The determination of which method to use was determined intraoperatively at the discretion of the surgeon. A Malecot catheter was chosen in cases which were felt to have greater degree of intraoperative bleeding to best tamponade the bleeding while continuing urinary decompression. All analyses were performed using SAS ® version 9.4 software (SAS Institute, Cary, North Carolina, USA). All testing was two-sided, and the probability of a Type I error was set at 0.05. The study was approved by the Institutional Review Board (IRB) at Indiana University.
RESULTS Our total study population included 126 patients with 63 standard and 63 PERC-tic PCNLs (Table 1). The mean age of the standard PCNL group was 53.8 years versus 55.0 years for the PERC-tic group. On univariate analysis, the PERC-tic group did have lower skin-to-stone distances (mean 9.4 cm versus 11 cm, p = 0.008), higher rate of secondary endourologic procedure (71% vs 30%, p< 0.0001), and lower 90 day SFR (63% vs 85%, p = 0.018). The groups did not differ with respect to mean age, BMI, change in hemoglobin, presence of postoperative Malecot nephrostomy catheter, renal bleeding, Guy’s stone score of four or three versus two or one, or 90 day hospital readmission rate.
As seen in Table 2, after controlling for age, skin-to-stone distance, Guy’s stone score of three or four, and change in hemoglobin, there was no statistical difference between the PERCtic technique versus standard PCNL with respect to stone clearance rate at the 90 day follow up appointment [adjusted odds ratio (aOR), 0.39; 95% confidence interval (CI), 0.13 – 1.1, p= 0.08]. As shown in Table 3, the use of the PERC-tic technique was associated with a 6 times greater odds of requiring a secondary endoscopic procedure (aOR, 6.0; 95% CI, 2.6 – 13.8, p<0.0001) after controlling for the same variables as previously mentioned. The change in hemoglobin was trending towards statistical significance between the two groups (aOR, 1.4; 95% CI, 0.99 – 2.0, p= 0.06). The residual fragments ranged from 2 mm to 1.2 cm. Secondary procedures performed were either ureteroscopy or additional PCNL. With respect to complications, the PERC-tic technique was not associated with higher odds of 90-day hospital readmission (Supplementary Table 1) after controlling for age, skin-tostone distance, Guy’s stone score, and change in hemoglobin. Supplementary Table 2 shows each complication from each group. The standard group were found to have eight complications and the PERC-tic group had five complications. The highest Clavien-Dindo classification in the standard group was IIIb and the PERC-tic group was IVa. As seen in Figure 1, 13.0% of standard PCNL patients had a Malecot catheter for postoperative drainage versus 25.4% in the PERC-tic group. The majority of patients had a 10-Fr nephrostomy tube in both the standard PCNL and PERC-tic group, 81.2% and 71.6%, respectively.
DISCUSSION PCNL can vary significantly in procedural difficulty and morbidity based on the complexity of the stone and renal anatomy11–14. Our study shows the PERC-tic technique for
renal access is a safe and feasible method when antegrade access into the ureter is not possible. After adjusting for demographic variables such as age and body habitus and stone complexity using the Guy’s stone score, the 90-day SFR for the PERC-tic technique was similar when compared to the standard PCNL cohort (64% vs 85%). Furthermore, the utilization of PERC-tic PCNL should prompt a surgeon to counsel the patient that the need to perform a secondary PCNL is greater due to a higher likelihood of residual stones after the primary PCNL. We found 6.0 times higher odds of needing a secondary procedure for residual stones when patients undergo the PERC-tic technique compared to a standard PCNL (p<0.0001). Despite a greater need for secondary procedures, we found no difference in the complication rate between the standard PCNL and PERC-tic groups. (12.6% vs 12.9%, respectively, p= 97). Currently, no study has examined the PERC-tic technique for patients with otherwise normal renal anatomy. Previously, Hulbert et al in 1986 and Kim et al in 2005 studied this approach with respect to the management of caliceal diverticula. We hypothesized that the PERC-tic procedure is associated with increased intraoperative hemorrhage. Without a wire down the ureter the kidney is more mobile during balloon dilation and advancement of the access sheath which we feel results in more trauma to the renal capsule and parenchyma. Moreover, all of the PERC-tic patients were originally planned to undergo standard PCNL. Only after we could not safely cannulate the ureter did we switch to the PERC-tic technique. This additional manipulation of the kidney would likely result in greater bleeding. On bivariate analysis there was no statistical difference in hemoglobin change between the standard PCNL and PERC-tic cohort (1.7 g/dl vs 1.4 g/dl, respectively, p= 0.08), CT evidence of a renal bleed (49.2% vs 47.6%, respectively, p= 0.85), or placement of a Malecot nephrostomy tube (14.2% vs 23.8%, respectively, p= 0.17). Despite the lack of evidence of increased bleeding, on multivariate
analysis, there is a significantly higher rate of secondary procedures to treat residual stones associated with PERC-tic PCNL, which we feel is partially a reflection of increased stone complexity and worse visualization during the primary procedure. Our data suggests standard PCNL should not be aborted when a wire cannot be advanced down the ureter. Instead, PERC-tic PCNL can be utilized to complete the surgery and achieve a suitable outcome. Furthermore, PERC-tic PCNL has similar overall patient morbidity as compared to standard PCNL; however, a secondary endourologic procedure may be required to achieve acceptable stone free rates. Other distinct advantages to the PERC-tic PCNL include: minimal additional equipment needed, no change in patient positioning, and ability to easily switch to this technique in the intra operative setting. PERC-tic PCNL may be considered as an additional tool in the armamentarium of urologists whom may have planned to perform a standard PCNL at the time. We utilized the PERC-tic technique as a last resort. We first attempted a standard lower pole puncture followed by upper or possibly mid pole puncture in each case. The majority of cases included partial or complete staghorn stones, which made it near impossible to facilitate anterograde wire access down the ureter. In these instances, the PERC-tic technique was then used. Alternate approaches to complex PCNL cases have been described 3–5,15–17. Studies have shown success with staged flexible ureteroscopy and combined prone split-leg URS/PCNL. Staged flexible ureteroscopy has been touted as a minimally invasive approach to treat large intrarenal calculi without significantly compromising stone clearance rates 18–20. The prone splitleg approach has been associated with a decreased operating room time, less manipulation of the patient, and greater versatility with respect to stone maneuverability along the length of the urinary tract compared to standard prone PCNL 21–24. However, for such a technique to be
applied for the cases presented in this study significant laser manipulation of the impacted stone and/or stenotic infundibulum would be necessary to gain percutaneous access with the aid of a ureteroscope. PERC-tic PCNL can be done at any point without additional preoperative planning and requires minimal additional equipment or personnel. This is a primary challenge with dual URS and PCNL procedures. Additionally, PERC-tic can render the patient stone free in one setting avoiding prolonged stenting and multiple anesthetics which can occur with staged URS. In an international multi institutional study, the 90 day SFR with simultaneous URS and PCNL was 71% similar to our study of 64% for the PERC-tic cohort 25. This study had only seven patients and only two had a Guy’s stone score four 25. Similar SFR between 71% to 97% have been reported or prone split-leg URS/PCNL in patients with significant stone burden by no score classification.22–24,26. In our study 81% of patients in the PERC-tic group had a Guy’s stone score of three or four. In the case of staged URS, stone free rates vary. Studies have ranged from a 58% to 95% stone clearance rate with a single URS and up to 87% and 96% with a second and third session of treatment, respectively 18,19. Breda et al showed an overall stone free rate of 93% with an average of 2.3 sessions of staged URS 20. The stone-free rate for PCNL also varies widely from 49% to 92% depending on patient positioning, stone factors, as well as a host of other variables 27–30. There are several possible explanations for the decreased 90-day SFR in the PERC-tic cohort compared to the standard PCNL cohort. The PERC-tic cohort represents a subset of patients who failed standard PCNL surgery at the time of their operation. Despite this, the SFR at 90 days appears similar to other techniques described in the literature for complex stone burden such as prone split-leg positioning and staged URS.
This study is not without limitations. First, this is a retrospective review of a single institution’s experience with PERC-tic technique. Intrinsic bias and confounding factors were anticipated 30, but attempts to control for these limitations with a logistic regression analysis have been demonstrated within this paper. Furthermore, although we report retrospective results, our data is prospectively collected. Second, the data was captured through an electronic medical recording system, and all data was extracted by three study authors. The clinical documentation practices may limit the precision of the data. For example, we could not ascertain the type of renal pole access for the standard PCNL cohort whether it was upper, middle, or lower pole. Unfortunately, not all of the fluoroscopic images were saved, so we cannot reliably determine the exact pole of puncture. However, to our knowledge, there is no longitudinal administrative database that collects the information of interest. The data in our study was collected from a robust electronic medical record system used for clinical and billing purposes. Third, it should be noted each CT was reviewed independently with respect to the presence of renal bleeding and not in a centralized fashion. Furthermore, we did not analyze exact stone size but rather used Guy’s stone score as a surrogate marker for renal stone complexity. We acknowledge stone size can be variable between Guys stone score of 3 versus 4. However, Guys stone score has been shown to accurately predict stone free rate after PCNL. Finally, our outcomes may not lend itself to generalizability as we are a large tertiary referral center.
CONCLUSION The PERC-tic technique is a safe and effective strategy when difficulties arise placing anterograde wire access into the renal collecting system and ureter. The stone free rate at 90 days for the PERC-tic technique is similar to the standard PCNL approach although there is a higher
need for secondary procedures. There does not appear to be a difference in hospital readmission or complication. Our findings will hopefully prompt surgeons to consider the PERC-tic technique instead of abandoning the percutaneous stone removal procedure if antegrade ureteral access cannot be achieved.
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doi:10.1089/end.2010.0424. 29. Ghani KR, Andonian S, Bultitude M, et al. Percutaneous Nephrolithotomy: Update, Trends, and Future Directions. Eur Urol. 2016;70(2):382-396. doi:10.1016/j.eururo.2016.01.047. 30. Carlson MDA, Morrison RS. Study Design, Precision, and Validity in Observational Studies. J Palliat Med. 2009;12(1):77-82. doi:10.1089/jpm.2008.9690.
Method of drainage post PCNL 0.9
81.2% 0.8
71.6%
0.7
Percentage
0.6 5 or 6 Fr ureteral catheter
0.5
10 Fr nephrostomy tube
0.4
Malecot catheter
0.3
25.4%
0.2 0.1
13.0% 5.8%
3.0%
0 Standard PCNL
PERC-tic
Table 1. Demographic and stone characteristics Standard Characteristic Total Age, years, mean (SD) Female Laterality BMI (SD) Skin-to-stone distance, cm, (SD) Change in hemoglobin, g/dl, mean (SD) Malecot catheter
n (%) 63 (50) 53.8 (17.2) 25 (39.7) Right Left Bilateral 21 26 16 32.7 (10.3) 11 (3.7) 1.7 (1.5)
PERC-tic n (%) 63 (50) 55.0 (16.5) 26 (51) Right Left Bilateral 13 20 30 31.3 (9.4) 9.4 (3.1) 1.4 (1.2)
Yes No Yes 9 54 15 Renal bleeding Yes No Yes 31 32 30 Guy’s stone score 4 or 3 2 or 1 4 or 3 44 19 51 Stone free at 90 day follow up Yes No Yes 40 7 30 Secondary procedure Yes No Yes 19 44 45 90 day hospital readmission Yes No Yes 8 55 8 Abbreviations: Standard deviation (SD); centimeter (cm) Referent groups are male, lack of Malecot catheter, and no renal bleeding
No 48 No 33 2 or 1 12 No 17 No 18 No 54
p-value 0.69 0.86
0.43 0.008 0.08 0.17 0.85 0.14 0.018 < 0.0001 0.97
Table 2. Influence of stone and patient characteristics on stone clearance rate at 90 day follow up Stone/Patient Characteristics Multivariable Adjusted OR (95% CI) p-value Age 0.99 (0.96, 1.0) 0.71 PERC-tic 0.39 (0.13, 1.1) 0.08 Skin-to-stone distance, cm 1.1 (0.97, 1.3) 0.13 Guy’s stone score 4 or 3 0.7 (0.20, 2.5) 0.58 Change in hemoglobin, g/dl 0.71 (0.25, 1.9) 0.51 Abbreviations: centimeter (cm) Referent groups are standard percutaneous nephrostomy technique and Guys stone score of 2 or 1
Table 3. Influence of stone and patient characteristics on need for secondary endourologic procedure Stone/Patient Characteristics Multivariable Adjusted OR (95% CI) p-value Age 0.99 (0.97, 1.0) 0.49 PERC-tic 6.0 (2.6, 13.8) <0.0001 Skin-to-stone distance 0.89 (0.79, 1.0) 0.08 Guy’s stone score 4 or 3 1.9 (0.74, 5.0) 0.18 Change in hemoglobin, g/dl 1.4 (0.99, 2.0) 0.06 Referent groups are standard percutaneous nephrostomy technique and Guys stone score of 2 or 1
Comparative study of percutaneous tic technique versus standard percutaneous nephrolithotomy Naveen Krishnan MD MS , Tim Large MD , Crystal Valadon BS , Amy Krambeck MD PII: DOI: Reference:
S0090-4295(20)30174-6 https://doi.org/10.1016/j.urology.2019.12.040 URL 21985
To appear in:
Urology
Received date: Revised date: Accepted date:
6 August 2019 4 December 2019 11 December 2019
Please cite this article as: Naveen Krishnan MD MS , Tim Large MD , Crystal Valadon BS , Amy Krambeck MD , Comparative study of percutaneous tic technique versus standard percutaneous nephrolithotomy, Urology (2020), doi: https://doi.org/10.1016/j.urology.2019.12.040
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Comparative study of percutaneous tic technique versus standard percutaneous nephrolithotomy
Naveen Krishnan, MD MS1, Tim Large, MD1, Crystal Valadon, BS2, Amy Krambeck, MD1 From Indiana University Department of Urology1 and Louisville School of Medicine2
Dr. Amy Krambeck is a consultant for Boston Scientific Corporation, Lumenis and Cook Medical
Corresponding Author: Amy E. Krambeck, MD Michael O. Koch Professor of Urology Indiana University/IU Health Physicians, 1801 Senate Blvd Suite 220, Indianapolis, IN 46212 Phone: 317-962-3700; Email: [email protected] Krishnan: [email protected]; Large: [email protected]; Valadon: [email protected]
Keywords: percutaneous nephrolithotomy, PCNL, renal access
Acknowledgements: None Financial Disclosures: None
There is no conflict of interest for any of the authors. There are no colored figures for this manuscript.
ABSTRACT Objective: To compare the PERC-tic technique, described as placement of dual wires under fluoroscopic guidance adjacent to the stone within the obstructed calyx, to standard percutaneous nephrolithotomy (PCNL) with working wires secured down the ureter. Materials and Methods: This is a retrospective cohort study of patients who underwent a PCNL procedure between October 2016 and November 2018. Patients undergoing the perc-tic technique were compared to patients undergoing standard PCNL. Regression models evaluated if PERC-tic PCNL was associated with equivalent stone-free rates to standard PCNL at 90 days, need for secondary procedures, and 90-day hospital readmission. Results: This study involved 126 PCNL cases of which 63 were done using the PERC-tic technique and 63 with standard PCNL. In multivariate analysis, there was no statistical difference in 90-day stone-free rate between standard PCNL and PERC-tic cohorts (p=0.08). We did note a 6 times higher likelihood of needing secondary procedures for residual stones in the PERC-tic versus standard PCNL groups (71% vs 30% p< 0.0001). There was no statistical significance in 90-day hospital readmission rates between groups (p=0.47). Conclusions: Our findings suggest similar stone free rate at 90 days and higher rates of secondary procedures after PERC-tic PCNL compared to the standard approach; however, there was no difference in complications. These findings may reflect decreased visualization with the PERC-tic technique or simply be reflective of the case difficulty requiring the use of the PERCtic technique. These findings can be used for patient counseling when considering this technique for complex stone disease.
INTRODUCTION Since first described by Fernstrom and colleagues in 1976, percutaneous nephrolithotomy (PCNL) has progressed into the surgical standard of care for the treatment of patients with large complex stone burdens 1-3. Notable improvements in both equipment and technique, including advancements in diagnostic imaging, reduction in the size and complexity of percutaneous surgical equipment, and novel ways to safely access the collecting system, are at the cornerstone of the PCNL evolution 2–5. These changes strive to reduce surgical morbidity while improving stone clearance rates. Due to its safety and efficacy, both American and European guideline panels recommend PCNL as the primary surgical intervention for complex stones greater than two centimeters 6 7. Establishing percutaneous access optimally occurs over a stiff wire extending through the calyx of entry down the ureter and terminating within the bladder. At times, anterograde advancement of a wire down the ureter is unsafe or not feasible. Examples where ureteral cannulation is less likely include cases involving a ureteropelvic junction (UPJ) obstruction, a target stone that lies within a diverticulum or obstructs the calyx or infundibulum of entry. The percutaneous diverticulum (PERC-tic) technique obviates the need for ureteral cannulation by coiling a working and safety wire in the punctured calyx, renal pelvis, or diverticulum prior to dilating the tract for placement of the percutaneous access sheath. This technique has been described in the treatment of caliceal diverticulum calculi, but has not been previously described for patients with other anomalies restricting antegrade ureteral access 8,9. Our study examines the use of the PERC-tic technique versus standard PCNL (where a working wire has successfully been positioned down the length of the ureter). In cases where PERC-tic technique is used, there is the perception that the renal unit is more mobile during the
balloon dilation and percutaneous access sheath advancement., In addition to the inherent challenges of treating stones that require the PERC-tic PCNL, visualization can be perceived as decreased secondary to bleeding after advancement of the access sheath into the mobile kidney The perceived increase in intraoperative bleeding during PERC-tic PCNL is insufficient enough to warrant transfusion but is felt to affect intraoperative vision. We, therefore, hypothesize that PERC-tic PCNL is safe but results in greater need for secondary endourologic procedures to render patients stone free.
MATERIALS AND METHODS Study population We conducted a retrospective cohort study of PCNL procedures completed between October 2016 to November 2018 based on our prospectively collected tertiary care institutional database. We considered each case with respect to number of renal units. We excluded any patients with significant anatomic anomalies including spinal deformity, horseshoe kidney, pelvic kidney, or renal transplantation. Surgical Technique All patients in this study were originally scheduled to undergo standard PCNL in the prone position. After it was determined that anterograde ureteral access intraoperatively could not be established, the PERC-tic technique was used. For patients undergoing standard PCNL, we would place an Amplatz Super Stiff™ guide wire down the ureter. We would then place an additional safety wire which was either a hybrid Sensor® polytetrafluoroethylene-nitinol guide wire with hydrophilic tip or a 0.038 Fr BARD® straight movable core guidewire. The tract was then dilated to 30 Fr and an access sheath was placed (Supplementary image 1).
For patients undergoing PERC-tic technique, anterograde ureteral access could not be established despite multiple attempts. Therefore, we would first coil a ZIPwire™ hydrophilic guide wire from Boston Scientific within the renal pelvis or obstructed calyx. We then used a ureteral catheter to replace this wire with a 0.038 Fr BARD® J movable core guidewire. We would then coil an additional J movable core guidewire as well using an 3mm Brite Tip TM interventional sheath from Cordis. We would ensure that there was an abundant amount of coiled wire to prevent tract dilation over the insubstantial portion of the wire. The tract was then dilated to 30 Fr using the BARD X-Force® N30 nephrostomy dilation catheter set. Once the stone burden was sufficiently removed, we always established anterograde access down the ureter using a wire to help stabilize the renal unit. All patients within both groups included only a single access for each kidney. None of the PERC-tic patients had standard access. Outcomes The primary outcome was stone-free rate (SFR) at 90 days follow up appointment as assessed by radiologic imaging [computerized tomography (CT), abdominal plain x-ray, or renal ultrasound]. All patients in this study had a CT of the abdomen and pelvis without contrast on post operative day one. If there were any residual fragments greater than two mm remaining, the patient was then taken for a secondary procedure either ureteroscopy or PCNL using the established tract. The secondary procedure occurred on post operative day two. The secondary outcomes in this study include rate of secondary procedure and rate of 90-day hospital readmission. Patients who were returning for a secondary endourologic procedure did not count as a hospital readmission. We controlled for patient demographic and stone factors including age, skin-to-stone distance, body mass index (BMI), Guy’s stone score 10, need for an 18 French
(Fr) Malecot nephrostomy tube post operatively, and renal bleeding. All Guy’s stone score 4 were staghorn stones. Our standard protocol is to leave a 10 Fr nephrostomy tube after PCNL; however, if there is significant intraoperative bleeding obscuring visualization we will leave an 18 Fr Malecot nephrostomy tube. The 18 Fr Malecot nephrostomy tube allows direct access to the ureter and maximizes urinary drainage. Renal bleeding was characterized as presence, on the postoperative day one CT scan, of a perinephric hematoma, an intra renal bleed or both. All patients were followed within 90 days with a CT of the abdomen and pelvis without contrast to assess stone free rate. All clinical data and imaging were independently reviewed by two urologists.
Statistical analyses We conducted a bivariate analyses to examine demographic and clinical factors among patients after undergoing standard versus PERC-tic PCNL. Specific variables of interest included, but were not limited to: age, gender, body mass index (BMI), change in hemoglobin between the pre operative and post operative day one setting, stone size and location, skin-tostone distance, and postoperative nephrostomy tube drainage. Additionally, stone complexity was graded using the Guy’s stone score, and any evidence of bleeding was assessed based on presence of a renal bleed on the postoperative CT. We used Student’s t-statistic and CochranMantel-Haenszel chi-square tests when appropriate. Second, we performed multivariable logistic regression analyses adjusting for the following variables: age, use of PERC-tic technique, skin-to-stone distance, Guy’s stone score of four, and change in hemoglobin. A logistic regression model with bias-corrected 95% confidence
intervals (CIs) was generated. The referent groups were always male patients, standard PCNL patients and Guy’s stone score of three, two, or one. Lastly, we examined the different methods of postoperative renal drainage between standard PCNL and PERC-tic patients. The different methods include a five or six Fr ureteral catheter, a 10-Fr nephrostomy catheter with or without a ureteral catheter, or an 18-Fr Malecot catheter. The determination of which method to use was determined intraoperatively at the discretion of the surgeon. A Malecot catheter was chosen in cases which were felt to have greater degree of intraoperative bleeding to best tamponade the bleeding while continuing urinary decompression. All analyses were performed using SAS ® version 9.4 software (SAS Institute, Cary, North Carolina, USA). All testing was two-sided, and the probability of a Type I error was set at 0.05. The study was approved by the Institutional Review Board (IRB) at Indiana University.
RESULTS Our total study population included 126 patients with 63 standard and 63 PERC-tic PCNLs (Table 1). The mean age of the standard PCNL group was 53.8 years versus 55.0 years for the PERC-tic group. On univariate analysis, the PERC-tic group did have lower skin-to-stone distances (mean 9.4 cm versus 11 cm, p = 0.008), higher rate of secondary endourologic procedure (71% vs 30%, p< 0.0001), and lower 90 day SFR (63% vs 85%, p = 0.018). The groups did not differ with respect to mean age, BMI, change in hemoglobin, presence of postoperative Malecot nephrostomy catheter, renal bleeding, Guy’s stone score of four or three versus two or one, or 90 day hospital readmission rate.
As seen in Table 2, after controlling for age, skin-to-stone distance, Guy’s stone score of three or four, and change in hemoglobin, there was no statistical difference between the PERCtic technique versus standard PCNL with respect to stone clearance rate at the 90 day follow up appointment [adjusted odds ratio (aOR), 0.39; 95% confidence interval (CI), 0.13 – 1.1, p= 0.08]. As shown in Table 3, the use of the PERC-tic technique was associated with a 6 times greater odds of requiring a secondary endoscopic procedure (aOR, 6.0; 95% CI, 2.6 – 13.8, p<0.0001) after controlling for the same variables as previously mentioned. The change in hemoglobin was trending towards statistical significance between the two groups (aOR, 1.4; 95% CI, 0.99 – 2.0, p= 0.06). The residual fragments ranged from 2 mm to 1.2 cm. Secondary procedures performed were either ureteroscopy or additional PCNL. With respect to complications, the PERC-tic technique was not associated with higher odds of 90-day hospital readmission (Supplementary Table 1) after controlling for age, skin-tostone distance, Guy’s stone score, and change in hemoglobin. Supplementary Table 2 shows each complication from each group. The standard group were found to have eight complications and the PERC-tic group had five complications. The highest Clavien-Dindo classification in the standard group was IIIb and the PERC-tic group was IVa. As seen in Figure 1, 13.0% of standard PCNL patients had a Malecot catheter for postoperative drainage versus 25.4% in the PERC-tic group. The majority of patients had a 10-Fr nephrostomy tube in both the standard PCNL and PERC-tic group, 81.2% and 71.6%, respectively.
DISCUSSION PCNL can vary significantly in procedural difficulty and morbidity based on the complexity of the stone and renal anatomy11–14. Our study shows the PERC-tic technique for
renal access is a safe and feasible method when antegrade access into the ureter is not possible. After adjusting for demographic variables such as age and body habitus and stone complexity using the Guy’s stone score, the 90-day SFR for the PERC-tic technique was similar when compared to the standard PCNL cohort (64% vs 85%). Furthermore, the utilization of PERC-tic PCNL should prompt a surgeon to counsel the patient that the need to perform a secondary PCNL is greater due to a higher likelihood of residual stones after the primary PCNL. We found 6.0 times higher odds of needing a secondary procedure for residual stones when patients undergo the PERC-tic technique compared to a standard PCNL (p<0.0001). Despite a greater need for secondary procedures, we found no difference in the complication rate between the standard PCNL and PERC-tic groups. (12.6% vs 12.9%, respectively, p= 97). Currently, no study has examined the PERC-tic technique for patients with otherwise normal renal anatomy. Previously, Hulbert et al in 1986 and Kim et al in 2005 studied this approach with respect to the management of caliceal diverticula. We hypothesized that the PERC-tic procedure is associated with increased intraoperative hemorrhage. Without a wire down the ureter the kidney is more mobile during balloon dilation and advancement of the access sheath which we feel results in more trauma to the renal capsule and parenchyma. Moreover, all of the PERC-tic patients were originally planned to undergo standard PCNL. Only after we could not safely cannulate the ureter did we switch to the PERC-tic technique. This additional manipulation of the kidney would likely result in greater bleeding. On bivariate analysis there was no statistical difference in hemoglobin change between the standard PCNL and PERC-tic cohort (1.7 g/dl vs 1.4 g/dl, respectively, p= 0.08), CT evidence of a renal bleed (49.2% vs 47.6%, respectively, p= 0.85), or placement of a Malecot nephrostomy tube (14.2% vs 23.8%, respectively, p= 0.17). Despite the lack of evidence of increased bleeding, on multivariate
analysis, there is a significantly higher rate of secondary procedures to treat residual stones associated with PERC-tic PCNL, which we feel is partially a reflection of increased stone complexity and worse visualization during the primary procedure. Our data suggests standard PCNL should not be aborted when a wire cannot be advanced down the ureter. Instead, PERC-tic PCNL can be utilized to complete the surgery and achieve a suitable outcome. Furthermore, PERC-tic PCNL has similar overall patient morbidity as compared to standard PCNL; however, a secondary endourologic procedure may be required to achieve acceptable stone free rates. Other distinct advantages to the PERC-tic PCNL include: minimal additional equipment needed, no change in patient positioning, and ability to easily switch to this technique in the intra operative setting. PERC-tic PCNL may be considered as an additional tool in the armamentarium of urologists whom may have planned to perform a standard PCNL at the time. We utilized the PERC-tic technique as a last resort. We first attempted a standard lower pole puncture followed by upper or possibly mid pole puncture in each case. The majority of cases included partial or complete staghorn stones, which made it near impossible to facilitate anterograde wire access down the ureter. In these instances, the PERC-tic technique was then used. Alternate approaches to complex PCNL cases have been described 3–5,15–17. Studies have shown success with staged flexible ureteroscopy and combined prone split-leg URS/PCNL. Staged flexible ureteroscopy has been touted as a minimally invasive approach to treat large intrarenal calculi without significantly compromising stone clearance rates 18–20. The prone splitleg approach has been associated with a decreased operating room time, less manipulation of the patient, and greater versatility with respect to stone maneuverability along the length of the urinary tract compared to standard prone PCNL 21–24. However, for such a technique to be
applied for the cases presented in this study significant laser manipulation of the impacted stone and/or stenotic infundibulum would be necessary to gain percutaneous access with the aid of a ureteroscope. PERC-tic PCNL can be done at any point without additional preoperative planning and requires minimal additional equipment or personnel. This is a primary challenge with dual URS and PCNL procedures. Additionally, PERC-tic can render the patient stone free in one setting avoiding prolonged stenting and multiple anesthetics which can occur with staged URS. In an international multi institutional study, the 90 day SFR with simultaneous URS and PCNL was 71% similar to our study of 64% for the PERC-tic cohort 25. This study had only seven patients and only two had a Guy’s stone score four 25. Similar SFR between 71% to 97% have been reported or prone split-leg URS/PCNL in patients with significant stone burden by no score classification.22–24,26. In our study 81% of patients in the PERC-tic group had a Guy’s stone score of three or four. In the case of staged URS, stone free rates vary. Studies have ranged from a 58% to 95% stone clearance rate with a single URS and up to 87% and 96% with a second and third session of treatment, respectively 18,19. Breda et al showed an overall stone free rate of 93% with an average of 2.3 sessions of staged URS 20. The stone-free rate for PCNL also varies widely from 49% to 92% depending on patient positioning, stone factors, as well as a host of other variables 27–30. There are several possible explanations for the decreased 90-day SFR in the PERC-tic cohort compared to the standard PCNL cohort. The PERC-tic cohort represents a subset of patients who failed standard PCNL surgery at the time of their operation. Despite this, the SFR at 90 days appears similar to other techniques described in the literature for complex stone burden such as prone split-leg positioning and staged URS.
This study is not without limitations. First, this is a retrospective review of a single institution’s experience with PERC-tic technique. Intrinsic bias and confounding factors were anticipated 30, but attempts to control for these limitations with a logistic regression analysis have been demonstrated within this paper. Furthermore, although we report retrospective results, our data is prospectively collected. Second, the data was captured through an electronic medical recording system, and all data was extracted by three study authors. The clinical documentation practices may limit the precision of the data. For example, we could not ascertain the type of renal pole access for the standard PCNL cohort whether it was upper, middle, or lower pole. Unfortunately, not all of the fluoroscopic images were saved, so we cannot reliably determine the exact pole of puncture. However, to our knowledge, there is no longitudinal administrative database that collects the information of interest. The data in our study was collected from a robust electronic medical record system used for clinical and billing purposes. Third, it should be noted each CT was reviewed independently with respect to the presence of renal bleeding and not in a centralized fashion. Furthermore, we did not analyze exact stone size but rather used Guy’s stone score as a surrogate marker for renal stone complexity. We acknowledge stone size can be variable between Guys stone score of 3 versus 4. However, Guys stone score has been shown to accurately predict stone free rate after PCNL. Finally, our outcomes may not lend itself to generalizability as we are a large tertiary referral center.
CONCLUSION The PERC-tic technique is a safe and effective strategy when difficulties arise placing anterograde wire access into the renal collecting system and ureter. The stone free rate at 90 days for the PERC-tic technique is similar to the standard PCNL approach although there is a higher
need for secondary procedures. There does not appear to be a difference in hospital readmission or complication. Our findings will hopefully prompt surgeons to consider the PERC-tic technique instead of abandoning the percutaneous stone removal procedure if antegrade ureteral access cannot be achieved.
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Method of drainage post PCNL 0.9
81.2% 0.8
71.6%
0.7
Percentage
0.6 5 or 6 Fr ureteral catheter
0.5
10 Fr nephrostomy tube
0.4
Malecot catheter
0.3
25.4%
0.2 0.1
13.0% 5.8%
3.0%
0 Standard PCNL
PERC-tic
Table 1. Demographic and stone characteristics Standard Characteristic Total Age, years, mean (SD) Female Laterality BMI (SD) Skin-to-stone distance, cm, (SD) Change in hemoglobin, g/dl, mean (SD) Malecot catheter
n (%) 63 (50) 53.8 (17.2) 25 (39.7) Right Left Bilateral 21 26 16 32.7 (10.3) 11 (3.7) 1.7 (1.5)
PERC-tic n (%) 63 (50) 55.0 (16.5) 26 (51) Right Left Bilateral 13 20 30 31.3 (9.4) 9.4 (3.1) 1.4 (1.2)
Yes No Yes 9 54 15 Renal bleeding Yes No Yes 31 32 30 Guy’s stone score 4 or 3 2 or 1 4 or 3 44 19 51 Stone free at 90 day follow up Yes No Yes 40 7 30 Secondary procedure Yes No Yes 19 44 45 90 day hospital readmission Yes No Yes 8 55 8 Abbreviations: Standard deviation (SD); centimeter (cm) Referent groups are male, lack of Malecot catheter, and no renal bleeding
No 48 No 33 2 or 1 12 No 17 No 18 No 54
p-value 0.69 0.86
0.43 0.008 0.08 0.17 0.85 0.14 0.018 < 0.0001 0.97
Table 2. Influence of stone and patient characteristics on stone clearance rate at 90 day follow up Stone/Patient Characteristics Multivariable Adjusted OR (95% CI) p-value Age 0.99 (0.96, 1.0) 0.71 PERC-tic 0.39 (0.13, 1.1) 0.08 Skin-to-stone distance, cm 1.1 (0.97, 1.3) 0.13 Guy’s stone score 4 or 3 0.7 (0.20, 2.5) 0.58 Change in hemoglobin, g/dl 0.71 (0.25, 1.9) 0.51 Abbreviations: centimeter (cm) Referent groups are standard percutaneous nephrostomy technique and Guys stone score of 2 or 1
Table 3. Influence of stone and patient characteristics on need for secondary endourologic procedure Stone/Patient Characteristics Multivariable Adjusted OR (95% CI) p-value Age 0.99 (0.97, 1.0) 0.49 PERC-tic 6.0 (2.6, 13.8) <0.0001 Skin-to-stone distance 0.89 (0.79, 1.0) 0.08 Guy’s stone score 4 or 3 1.9 (0.74, 5.0) 0.18 Change in hemoglobin, g/dl 1.4 (0.99, 2.0) 0.06 Referent groups are standard percutaneous nephrostomy technique and Guys stone score of 2 or 1