Abstract
Objective
To evaluate the efficacy and safety of a novel endoscopic dilation (END) method during percutaneous nephrolithotomy under ultrasonographic guidance.
Methods
We retrospectively reviewed the clinical records of 138 patients who underwent percutaneous nephrolithotomy from June 2020 to December 2021. The patients were divided into three groups based on the method of nephrostomy tract creation: those who underwent fascial Amplatz serial fascial dilation (AMD) (n = 45), one-shot dilation (OSD) (n = 45), and END (n = 48). For END, a 20-Fr dilator with sheath was accessed over the first guidewire. A second guidewire was inserted into the collecting system via the endoscope. The nephroscope was then accessed to enlarge the renal puncture point using both guidewires. Demographic variables and important intraoperative and postoperative findings were compared among the three groups.
Results
The preoperative characteristics were similar among the three groups. The END group had a significantly shorter access time than both the AMD and OSD groups and significantly less severe hemoglobin loss than the OSD group. There were no significant differences in the other important perioperative findings.
Conclusion
Use of this novel END method with two guidewires may be associated with less blood loss and a reduced access time.
Keywords
Introduction
The prevalence of renal calculi has been steadily increasing worldwide during the past four decades. 1 Percutaneous nephrolithotripsy (PCNL) is considered a first-line treatment for large and complex renal calculi. 2 The crucial steps in PCNL are renal puncture and tract dilation. Although fluoroscopy is commonly used for PCNL procedures, ultrasonographic guidance offers the advantages of being radiation-free 3 and less expensive. 4 Ultrasound-guided PCNL is widely performed in many institutions in China. However, the learning curve for this technique can be challenging for inexperienced surgeons because unlike in fluoroscopy, the establishment of access in ultrasound-guided procedures is not precisely monitored in real time. 5 Although ultrasound-guided PCNL has gained popularity, it is associated with potential complications such as renal hemorrhage, collecting system perforation, and urosepsis. 6 Four dilation methods are currently used for access establishment: Amplatz serial fascial dilation (AMD), Alken metal telescopic dilation, balloon dilation, and one-shot dilation (OSD). 7 AMD has been the most widely used method for establishing tract access during the last few decades. However, gradual facial dilations are often associated with a prolonged access time and increased X-ray exposure. 8 OSD has been proposed to simplify the dilation process. Systematic reviews have shown that compared with gradual dilations, the OSD technique can reduce the access time, fluoroscopy time, and postoperative hemoglobin concentration.8,9 However, Frattini et al. 10 highlighted several contraindications for OSD, such as a history of open renal surgery, pediatric or adolescent patients, and renal hypermobility. Additionally, OSD may lead to greater renal tissue damage. 11 Another technique, balloon dilation, has shown promise in reducing the access time and the degree of postoperative hemoglobin decline. 12 However, the high cost of balloon dilation, particularly in developing countries, is a significant limitation. 13
Use of a guidewire plays an important role in percutaneous tract establishment. Chung et al. 14 reported a modified nephrostomy tract dilation technique using guidewire traction. Urologist-established access should be effective and safe. Therefore, we have developed a novel dilation method for endoscopic manipulation over two guidewires. During dilation using this novel method, a 20-Fr dilator with matched sheath is directly accessed over the first J-tip guidewire. After the dilator has been removed, a second guidewire is inserted into the collecting system via the endoscope. The nephroscope is then accessed to enlarge the renal puncture point under the guidance of both guidewires. The objective of this retrospective study was to evaluate the efficacy and safety of this new endoscopic dilation (END) technique and compare it with the commonly used AMD and OSD methods.
Methods
We retrospectively reviewed 138 patients who underwent PCNL at our department from June 2020 to December 2021. All patients had kidney stones with a diameter of ≥2 cm or upper ureteral stones with a diameter of ≥1.5 cm. Patients with a urinary malformation, bleeding disorder, or severe cardiopulmonary disease were excluded. Patients with complete staghorn stones that occupied most of the collecting system were excluded from the study because standard PCNL was performed to remove the stones using a pneumatic and ultrasonic endoscopic lithotripter (EMS-IV Swiss LithoClast; EMS, Nyon, Switzerland). The patients were divided into three groups according to the dilation method used: the AMD group (n = 45), the OSD group (n = 45), and the END group (n = 48). The AMD or OSD technique was randomly performed from June 2020 to June 2021, and the END technique was performed in consecutive patients from July 2021 to December 2021. All PCNL procedures were performed by a single surgeon with experience performing more than 300 PCNL operations. This study was approved by the Ethics Committee of Nanjing First Hospital (approval number: KY202019-13). Written consent was not required because of the retrospective nature of the study and the anonymization of patient data prior to analysis. The reporting of this study conforms to the STROBE guidelines. 15
All patients underwent preoperative evaluation with non-contrast computed tomography and routine blood tests. A 5-Fr ureteral catheter was inserted retrogradely with the patient in the lithotomy position under general anesthesia. The patient was then placed in the prone position. A 22-gauge needle was inserted into the desired calyx guided by ultrasound (Mindray Medical International, Shenzhen, China) using the SVOF technique (short-principle, vertex-principle, obtuse-principle, and fornix-principle), which is commonly used by some Chinese urologists. 16 Specifically, the posterior calyx containing stones was chosen as the target calyx and was positioned closer to the ultrasound probe than the other calices (vertex-principle), the percutaneous access was established through the tip of the renal papilla in the target calyx (fornix-principle), the passage length from the skin to the target calices was minimized and kept as short as possible (short-principle), and the angle between the long axis of the access and other renal calices containing stones was kept obtuse (obtuse-principle). Following establishment of access, a J-tip guidewire (Shagong Medical Technology Co., Ltd., Suzhou, China) was inserted into the collecting system. In the AMD group, the tract was dilated using serial dilations from 8 to 18 Fr over the J-tip guidewire, until a 20-Fr sheath could be passed through the last dilator (Shagong Medical Technology Co., Ltd.). In the OSD group, a 20-Fr dilator with matched sheath was directly accessed over the J-tip guidewire, followed by removal of the dilator while holding the sheath in position.
In the END group, after needle puncture and insertion of the J-tip guidewire, a 20-Fr dilator with matched sheath was directly accessed over the J-tip guidewire, and the depth of the sheath into the body was 0.5 cm less than the depth of the puncture needle (Figure 1). After the dilator was removed, a nephroscope (Richard Wolf, Vernon Hills, IL, USA) was accessed through the sheath to observe whether perforation of the renal collecting system, guidewire dislodgement, or renal hemorrhage had occurred. As a result, the sheath was still outside the renal parenchyma with only a small puncture on the renal cortex (Figure 2(a)). A second guidewire was then inserted into the collecting system via the endoscope (Figure 2(b)). While passing through the renal puncture under the guidance of the second Zebra guidewire (Boston Scientific, Marlborough, MA, USA), the nephroscope compressed the J-tip guidewire, resulting in reverse movement of the guidewire. The force generated by this reverse movement cut the kidney tissue. A combined force of the nephroscope and J-tip guidewire was formed on the puncture point plane, which cut the renal tissue in the transverse direction and dilated the tract access (Figure 2(c)). When the renal stone was visualized, the sheath was gently rotated into the targeted calyx (Figure 2(d)). The renal stones were fragmented and removed by yttrium-aluminum-garnet laser lithotripsy (Rankeen, Shanghai, China). At the end of the procedure, a double J stent was inserted into the ureter. The nephrostomy tube was removed on postoperative day 3 to 5. The double J stent was removed at approximately 1 month postoperatively.
Procedure for guidewire insertion and tract dilation.
Procedure for guidewire insertion, dilation monitoring, and sheath access.
The patients underwent kidney, ureter, and bladder radiography or non-contrast computed tomography to determine the stone-free status. If no residual stone was present or the diameter of the residual stone was <4 mm, the patient was considered stone-free. The access time was defined as the time from needle puncture to direct observation of the collecting system under nephroscopy. The operation time was defined as the time from placement of the ureteral catheter to placement of the percutaneous nephrostomy catheter at the end of the procedure. The hemoglobin loss was calculated by subtracting the last preoperative hemoglobin concentration from the first postoperative hemoglobin concentration, and all patients received their first postoperative check-up without blood transfusion. The postoperative complications were stratified according to the modified Clavien grading system. 17 Grade 1 complications, which included postoperative fever, were defined as all events that, if left untreated, would spontaneously resolve or require only simple bedside intervention. Blood transfusion was classified as a grade 2 complication. Grade 3 complications, which included embolization, were defined as conditions that necessitated surgical, endoscopic, or radiologic intervention. Neighboring organ injuries and organ failure were classified as grade 4 complications, and death was considered a grade 5 complication.
Statistical analysis
Statistical analysis was performed using SPSS Version 20.0 (IBM Corp., Armonk, NY, USA). Analysis of variance was used to determine differences in normally distributed continuous data between groups. Multiple independent-samples non-parametric tests were used for data with unequal variances. The χ2 test or Fisher’s exact was performed to examine the potential differences in binary variables between groups. A P value of <0.05 was considered statistically significant.
Results
In total, 138 patients who underwent PCNL were divided into three groups. The demographic data, stone size, grade of hydronephrosis, and history of ipsilateral renal surgery were similar among the three groups (Table 1), indicating comparable preoperative characteristics. The mean access time in the END group (4.33 ± 0.63 minutes) was significantly shorter than that in the AMD and OSD groups (5.78 ± 0.82 and 4.82 ± 1.23 minutes, respectively) (P < 0.05) (Table 2). The mean operation time in the AMD, OSD, and END groups was 98.0 ± 38.3, 105.7 ± 32.2, and 106.5 ± 39.5 minutes, respectively, with no significant difference. Significantly less severe hemoglobin loss was observed in the END than OSD group (0.99 ± 0.73 vs. 1.72 ± 1.00 g/dL, respectively; P < 0.05) (Table 2). There was no statistically significant difference in hemoglobin loss between the AMD and END groups (1.16 ± 0.95 and 0.99 ± 0.73 g/dL, respectively). The rates of blood transfusion in the AMD, OSD, and END groups were not significantly different (2%, 7%, and 4%, respectively). Angiography and renal artery subsegmental embolization were performed in four patients (one in the AMD group and three in the OSD group) because of a postoperative decrease in hemoglobin, whereas no patient received embolization in the END group. The causes of acute renal hemorrhage were renal artery injury induced by overshooting (two patients in the OSD group) and postoperative renal pseudoaneurysms (one patient each in the AMD and OSD groups). The rate of embolization did not differ significantly among the three groups. Two tract dilations in the OSD group failed because of guidewire displacement, but there was no significant difference in the failure rate of access among all groups. No significant difference was observed in postoperative fever among the three groups. The stone-free rates were similar in all three groups (84% in AMD and OSD groups and 82% in END group). There was no significant difference in the mean number of days to nephrostomy removal or the mean duration of hospital stay among the three groups. No major complications such as pleural injury, visceral injury, or septic shock occurred in any of the groups.
Demographic variables.
Data are presented as mean ± standard deviation or n (%).
AMD, Amplatz serial fascial dilation; OSD, one-shot dilation; END, endoscopic dilation.
Important intra- and postoperative findings.
Data are presented as mean ± standard deviation or n (%).
AMD, Amplatz serial fascial dilation; OSD, one-shot dilation; END, endoscopic dilation.
Discussion
The establishment of safe and efficient percutaneous access is crucial for successful PCNL. In this study, we found that the access time in the END group was significantly shorter than that in both the OSD and AMD groups. AMD has drawbacks, including a prolonged tract dilation time and aggravation of renal parenchymal damage, because of the higher numbers of exchanges and dilations. In the present study, the access time in the OSD group was significantly shorter than that in the AMD group. Additionally, the access time in the END group was significantly shorter than that in the OSD group. This non-X-ray-guided OSD technique is less precise, often resulting in the puncture sheath not entering the renal collecting system after single-step dilation. In such cases, OSD must be converted to a procedure involving multiple dilations, which may increase the median access time. The END procedure was visualized under nephroscopy, which may facilitate more precise and rapid dilation than in the OSD method, particularly when performing ultrasound-guided PCNL. In our study, there were two cases of failed dilation in the OSD group, whereas all cases in the END group were successful. The need for re-dilation in the OSD group due to failed dilation also increased the average time for tract establishment. The failure of tract dilation during PCNL can be attributed to factors such as an abnormally mobile kidney, fibrotic scarring from previous open surgery, and guidewire slippage.18–20 The last step of our novel END technique is monitored under nephroscopy, which prevents displacement of the guidewire and ensures the safety of the dilation. The Zebra guidewire may slip out of the renal collecting system after insertion if the undilated target calices are filled with stones. Because of the lack of space in the calices, the stones can easily cause the tip of Zebra guidewire to divert and slip out, which may lead to displacement of the guidewire. The J-tip guidewire is relatively short and its tip is not easily diverted; thus, it can be used as the first guidewire for access to the renal collection system through the puncture needle without X-ray monitoring and was chosen for this purpose in our study. After successful puncture, we inserted the J-tip guidewire and used the Zebra guidewire was used as the second guidewire. When the nephroscope guided by the Zebra guidewire passes through the puncture point, coordinated transverse motion of the nephroscope and J-tip guidewire occurs in the reverse direction. This coordinated motion may reduce the hypermobility of the kidney and minimize forward displacement of the dilator. This double-guidewire technique, which overcomes kidney hypermobility, may be helpful for successful dilation.
AMD is the most widely used dilation method. However, the multiple dilations prolong the X-ray exposure, which is harmful for both surgeons and patients during X-ray guided PCNL. 21 Several attempts have been made to simplify this technique. Frattini et al. 10 reported that the OSD method simplifies the dilation process and significantly reduces the X-ray exposure time compared with conventional dilators. Srivastava et al. 13 and Xiong et al. 22 found that the OSD method was associated with a shorter access time and equal complications compared with the AMD method. Our study also demonstrated that the OSD method reduced the access time during the ultrasound-guided procedure compared with the AMD method. Most PCNL procedures are performed under fluoroscopic guidance. However, a previous study demonstrated that ultrasound-guided PCNL reduces cost and radiation exposure and even has the same effect in some special cases, such as pediatric patients with calculi 23 and patients with a retrorenal colon. 24 Only ultrasound has been used in all three dilation procedures in our urology operating room. Because the dilation is not monitored in real time under ultrasound guidance, it is difficult for urologists establish precise access. Although OSD is a simplified technique, there is certain difficulty in its application because of the lack of X-ray monitoring; therefore, the puncture sheaths were sometimes out of place or even outside the renal capsule when the dilators were rotated into the collecting system in the OSD group of our study. Surgeons face a great challenge if the access tract is lost during the dilation procedure because they would have to establish access through puncture and dilation again under enormous pressure. A previous study revealed tract dilation failure rates of 6% (4/67) in the AMD group and 13% (3/23) in the OSD group. 22 Ozok et al. 25 speculated that perirenal fibrotic scarring and renal hypermobility were the main reasons for dilation failure. To overcome kidney mobility, Lezrek et al. 26 complemented the OSD method with the use of bi-prong forceps. The bi-prong forceps was inserted into the renal capsule puncture site, and forceps dilatation was then used to enlarge the renal capsule puncture and dilate the tract. Javali et al. 27 reported a novel dilation method and monitored its progress both endoscopically and fluoroscopically in cases in which the guidewire failed to pass into the ureter. In our study, the END method was also a modified technique based on OSD method. In contrast to the OSD method without X-ray monitoring, the dilation procedure in END is monitored under nephroscopy, which makes dilation easier and safer. Based on the fact that there were two failed dilations in the OSD group but none in the END group, we postulate that the END method may increase the dilation success rate.
In our study, less severe hemoglobin loss was observed in the END group (0.99 ± 0.73 g/dL) than in the OSD group (1.72 ± 1.00 g/dL). While passing through the renal puncture under the guidance of the second Zebra guidewire, the nephroscope compresses the J-tip guidewire, resulting in reverse movement of the guidewire. The force generated by this reverse movement cuts the kidney tissue. A combined force of the nephroscope and J-tip guidewire is formed on the puncture point plane, which cuts the renal tissue in the transverse direction and dilates the tract access. Compared with the shearing forces of sequential dilators, the blunt forces generated by the coordinated motion of the nephroscope and the J-tip guidewire in the transverse direction cause less tissue damage. Nalbant et al. 28 reported that balloon dilation that radially expanded the renal capsule puncture resulted in less bleeding. This principle of the END method is somewhat similar to balloon dilation. Kessaris et al. 29 stated that half of the bleeding incidents occurred during tract creation. Stoller et al. 30 demonstrated that perforation of the collecting system was the major factor attributed to severe bleeding in PCNL. In the END procedure, the tract access was observed under endoscopy. If severe bleeding occurs in the tract access, the percutaneous access should be resolutely abandoned. Because the sheath does not enter the collecting system, the puncture channel space is relatively narrow and separate from the renal collecting system. Thus, if venous bleeding occurs in the puncture channel, hemostasis can be achieved through blood clot formation. Although no access was abandoned because of severe bleeding in the END group of our study, we believe that observing the severity of bleeding of the puncture access under endoscopy can reduce the incidence of hemorrhage and renal artery embolism.
This study had three main limitations. The main limitation is the single-center retrospective study design. Given the limitations of retrospective research, the non-randomized sample allocation may have biased the final results of our study. Second, the balloon dilation method was not compared with the other techniques because of the cost limitation of medical insurance in China. Third, there was potential for damage to the optics of the nephroscope, especially in patients with a large stone burden and impacted calculi. However, the proportion of such patients in this study is relatively small.
Conclusion
The last step of our novel END technique is monitored under nephroscopy, which may prevent guidewire slippage and dilation failure. Use of this novel END method with two guidewires may be associated with a shorter access time and less blood loss during ultrasound-guided percutaneous tract creation. The END method may make dilation easier and safer.
Footnotes
Acknowledgment
The authors thank Changcheng Zhou for assisting with the statistical analysis.
Author contributions
Quanliang Dou and Zhiqiang Qin contributed equally to this work. Ruipeng Jia designed the study and revised the manuscript. Rongfei Li and Jingyu Liu collected the data. Quanliang Dou and Zhiqiang Qin analyzed the data and wrote the first draft of this manuscript.
Data availability statement
The datasets generated during this study are available from the corresponding author upon reasonable request.
Declaration of conflicting interests
The authors declare that there is no conflict of interest.
Funding information
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.