Super‐stiff guidewire or loach guidewire during percutaneous nephrolithotomy?

Abstract Objectives The objectives of this work are to compare the outcomes between loach guidewire and super‐stiff guidewire during percutaneous nephrolithotomy (PCNL) and find potential indications of different guidewires. Patients and methods We retrospectively reviewed our institutional PCNL database from 2017 to 2021. Patients who underwent PCNL guided by loach guidewire were assigned to group A (489 patients); patients who received super‐stiff guidewire were assigned to group B (269 patients). Preoperative demographic data, intraoperative parameters, and postoperative complications were compared. The conditions and reasons of failed placement of guidewire needed readjustment were evaluated as well. Results Preoperative demographic data and most intraoperative parameters were not statistically different between the groups. Postoperative Clavien–Dindo complications were also comparable, with low rate of complications. However, failed placement of guidewire more occurred in group A (8.2% vs. 4.0%, respectively, p = 0.03). Compared with the super‐stiff guidewire, the loach guidewire was easier pass/slip into any place either it be perinephric or blood vessels. In most failed group A cases and all failed group B cases, the guidewire was placed in the perirenal fat. Six patients (15%) in group A, the guidewires entered into vessels. Conclusions Our results support that the faulty placement of loach guidewire is significantly more common compared with super‐stiff guidewire. Double confirmation is needed to prevent a major complication out of wrong dilatation whenever there is doubt about the wrong location of the guidewire.

looking for the better one, and their role still remains not well clarified.
Some authors prefer to choose the loach guidewire during PCNL 20,21 while others routinely use the super-stiff guidewire. 22,23 Both loach guidewire and super-stiff guidewire have been widely used, but the indications and the outcomes associated are poorly defined. Trying to give a contribution in this field, we designed the present study, aimed to compare the outcomes between loach guidewire and super-stiff guidewire during PCNL.
The secondary outcome of the study was to assess the reasons for failed placement of guidewire and find potential indications of different guidewires.

| PATIENTS AND METHODS
After institutional review board approval of the First Hospital of Jilin University, we retrospectively reviewed the records of patients who underwent PCNL from 1 May 2017 to 30 October 2021. All methods were carried out in accordance with relevant guidelines and regulations. Informed consent was obtained from the patients. The patients were excluded if they received preoperative nephrostomy. Ultrasonography, intravenous urography, and/or computed tomography scan were preoperatively used to evaluate the complexity of stones and the presence of hydronephrosis. Based on whether it was loach or super-stiff guidewire, patients were divided into group A (loach guidewire group) and group B (super-stiff guidewire group). Patients' demographics and characteristics, intraoperative and postoperative parameters, were recorded. The style of stones and presence of hydronephrosis were analysed, and the reasons of failed placement of guidewire were also explored. All cases were performed by one surgeon who had successfully finished more than 3000 cases of PCNL.
Clavien-Dindo classification was used to grade the PCNL-related complications. 24 All procedures performed in studies involving human participants were obtained from the institutional ethics committee of the First Hospital of Jilin University, Changchun, China.
The procedures were performed under general anaesthesia in both groups. After a 5-French external ureteral catheter was inserted in a retrograde fashion into the renal pelvis or the upper ureter in a lithotomy position (in order to be prepared for potential retrograde saline injection), the patient was placed in prone position on the UROSKOP Access surgery bed (Siemens, Germany). Such an X-ray Residual fragments ≤4 mm were accepted as stone free as previously described, and postoperative instant stone free rate (SFR) was evaluated at the end of the surgery based on the ultrasound and Xray images. 25 The definition of a failed placement or misplacement of guidewire is that the guidewire does not enter into the collecting system, which is confirmed by endoscopy and/or fluoroscopy. Operation time was defined from the start of retrograde insertion to the completion of nephrostomy tube placement.
Results were reported by descriptive statistics. Continuous variables were reported as medians with interquartile range, and categorical variables were reported as frequencies and proportions. Continuous variables were compared using Mann-Whitney U test, and categorical variables were compared using chi-square test. Subanalysis was performed to compare the failed placement of guidewires between loach and super-stiff guidewires using chi-square test. All p values were two-tailed, and p < 0.05 was considered significant. Statistical analysis was performed using SPSS software package (versions 17.0, SPSS, Inc., Chicago, IL, USA).

| RESULTS
The characteristics of loach guidewire group (group A) and superstiff guidewire group (group B) patients are reported in Table 1.
There were no statistically significant differences between male/ female ratio, mean age, body mass index, left/right side, ASA  (Table 3). Further analysis has shown that type of stones or presence of hydronephrosis was not significantly different between both group A and B (p = 0.828 and 0.609, respectively). In group B, all wires were located in the perirenal space in the failed cases ( Figure 2). However, guidewires were located in the perirenal space in 85.0% failed patients, and they misentered into blood vessels in 15% patients in group A ( Figure 3A,B).

| DISCUSSION
PCNL is a gold standard therapy for large and complex renal stones.

However, despite both American Urological Association and
European Association of Urology recommend PCNL as the first-line therapy for patients with renal stones >20 mm, complications still occur in 1-34% of patients. 2,3,26,27 How to decrease the rate of complications, especially severe renal bleeding, is still challenging. F I G U R E 3 Loach guidewire was misplaced into inferior vena cava.
In this study, we found no differences in using the two aforementioned guidewires. Postoperative instant SFR were more than 86%, and most complications were grades I and II in the two groups. To our knowledge, this is the first study that directly compare the use of loach and super-stiff guidewires during PCNL, showing that both of them are safe and effective, while faulty placement of loach guidewire is significantly more common compared with super-stiff guidewire. However, as a retrospective study, the selection bias was inherent and further prospective studies are needed. Although the surgeon in this study is experienced, the learning curve is still a confounding factor. It is better to list the type of stones. What is more, change of ipsilateral renal function and final SFR should also be evaluated. The slight size difference between the guidewires (0.032 vs. 0.035 in) could also be a confounding issue with a thinner wire prone to bending and dislodgement. The imbalance in the number of participants is indeed an objective fact, which is also one of the shortcomings in this study.
In conclusion, the faulty placement of loach guidewire is significantly more common compared with super-stiff guidewire. Hence, any endourologist using loach guidewire should know its inherent flexible quality. Double confirmation is needed using contrast injection/fluoroscopy to prevent a major complication out of wrong dilatation whenever there is doubt about the wrong location of the guidewire. Prospective studies are needed to confirm these findings.

CONFLICT OF INTEREST
None of the authors have any disclosures or conflicts of interest to report.

AUTHOR CONTRIBUTIONS
Xiaobo Ding designed and drafted the manuscript. Yuchuan Hou and Chunxi Wang concepted and revised the manuscript. Yanbo Wang concepted, designed and revised the manuscript.