Pediatric Mini-Percutaneous Nephrolithotomy Using Self-Retained Screwed Amplatz Sheath vs Ordinary Sheath

Abstract

Objective:

To evaluate the use of a new 16F mini-screwed sheath in pediatrics in comparison to a 16F ordinary Amplatz sheath.

Methods:

Sixty-seven patients <18 years with renal calculi between 1 and 2 cm who was a candidate for mini-percutaneous nephrolithotomy (mini-perc) between January 2019 and September 2021 were randomized by closed envelope in group A (34 patients) using new mini-screwed sheath and group B (33 patients) with ordinary mini-sheath. Patients with contraindications for percutaneous nephrolithotomy were excluded.

Results:

No significant difference was present between both groups according to patients and stone demographics. There was no significant difference between both groups regarding puncture site and number. The mean operative time was 51.25 ± 2.15 minutes and 52.35 ± 3.45 minutes in groups A and B, respectively. The fluoroscopy time was significantly lower in group A (2.1 ± 0.85 minutes) than in group B (2.9 ± 1.05 minutes). Tract loss was 18.2% in group B while 0% in group A. Although bleeding was less in group A, it was nonsignificant. The stone-free rate was (94.11%) and (90.9%) in group A and group B, respectively.

Conclusion:

Screwed sheath enables the urologist to have a stable track during pediatric mini-perc surgery despite the thin abdominal wall in the pediatric. The screw sheath provides significantly lower fluoroscopy time and decreases the need for nephrostomy tube insertion when compared with ordinary sheath in mini-perc renal surgery.

Introduction

Pediatric renal calculi are not an uncommon disease as it occurs in 50 patients in every 100,000 of the pediatric population.¹ The pediatric age group has a high risk of stone reformation. This increases the need for treatment options assuring a stone-free state with low radiation exposure.² Percutaneous nephrolithotomy is the first line in the treatment of renal stones >20 mm and lower calyceal stones more than 10 mm.^3,4

Percutaneous nephrolithotomy (PCNL) for pediatric renal calculi had been upgraded for smaller size endoscopy and track. Mini-percutaneous nephrolithotomy (mini-perc) is a surgery, in which a small tract below 20F with small sheathes and instruments is used. Miniaturization of pediatric percutaneous surgery was associated with low morbidity.^5,6

Many modifications of the standard PCNL had been emerged to decrease the complications and improve the outcomes of the technique.⁷

Miniaturization of access sheath size used in standard PCNL (range from 24 to 30F) to a smaller size in mini-perc surgery (range from 14 to 20F) had been associated with excellent results and less morbidity.^6,8 It was reported that some cases who planned for retrograde intrarenal surgery were diverted to percutaneous renal surgery.⁹

The stable tract is the most crucial step during the PCNL procedure. Unstable tracts are associated with prolonged operative time, increased risk of renal injury, and blood transfusion. This will be associated with high morbidity and low success rate.⁸

Our comparative work was done between the new screwed Amplatz sheath and the ordinary sheath in the treatment of pediatric renal stones with mini-perc in the supine position. Estimation of intraoperative complication rates was our main concern. In addition, we were minded with operation and fluoroscopy times.

Patients and Methods

Prospectively our case data were collected from our urology department between January 2019 and September 2021. Permissions obtained from Institutional Review Board (IRB), the ethical, and scientific committee, and from the patients and or their guardians were obtained as an initial step. Our cohort study was done on 67 patients presented to our department with single renal stones 1–2 cm and candidate for mini-PCNL. The enrolled patients in this study were randomized by the closed envelop method.

The patients were divided into two groups. Group A included 34 patients who underwent mini-perc using the newly designed screwed Amplatz sheath in the supine position, while group B included 33 patients who underwent mini-perc using the ordinary Amplatz sheath in the same position.

All patients in our study were <18 years with stones ranging from 1 to 2 cm on their maximum NCSCT (noncontrast spiral CT) dimensions.

Patients with a single kidney, uncontrolled coagulopathy, and a history of ipsilateral renal surgery were excluded.

All patients underwent history taking, clinical examination, and preoperative laboratory investigation (urine analysis, complete blood count liver function test, serum creatinine, prothrombin time, partial thromboplastin time, and international normalized ratio). Radiologic investigations, including pelvic abdominal ultrasonography, and low-dose unenhanced CT abdomen and pelvis were done as a routine for all patients preoperatively.

Screwed sheath features

The use of laparoscopic screwed trocars in penetration of the abdominal wall gave us the idea of the new screwed sheath to reach the kidney during percutaneous nephrolithotomy (PNL) surgery. The first study was done by Abdelwahab et al and the results were more promising in favor of a screwed sheath than an ordinary one.¹⁰ The sheath (16F calibers) was evolved by medical engineers of our hospitals. Registration code (international application NO PCT/EG 2020/000014) (Fig. 1).

FIG. 1.

16F pediatric screwed Amplatz sheath with external nut. Color images are available online.

Our sheath is radio-opaque semilucent and made of polytetrafluoroethylene.

From the base to the bevel end, the sheath has a 17 cm length and is composed of two portions:

Entry part: 16F caliber, a smooth outer surface, and 3 cm length. It has a beveled end marked with a colored ring (after which instrument activation can be done).

Surgeon part: 16F internal diameter, 22F external diameter (including the screw), 14 cm length, and screwed outer surface. The sheath wall thickness with its pitch is 2 mm, each pitch height is 1 mm, 1.5 widths, blunt edge, and the interpitch distance is 3 mm Nut fitting on the external screw.

Operative data

All patients in both groups underwent mini-perc in a supine position by a fixed operative staff. A line along the posterior axillary line was drawn before induction of general anesthesia. The patient was in the lithotomy position. Using appropriate size cystoscopy, a guide wire of 0.025-inch was inserted inside the targeted ureter, over which a 5F open tip ureteral catheter could negotiate the ureter safely. The flank-free modified supine position was used in all patients by putting a small cushion under the ipsilateral shoulder and buttock. Opacification of the system under fluoroscopy was done by injecting diluted contrast through the ureteric catheter.

An 18-gauge puncture needle was inserted into the collecting system targeting the posterior lower calyx in most cases. Hydrophilic sensor wire was introduced into the collecting system (ureter) through the puncturing needle and then gradual dilatation using facial dilators. Central metallic Alken was inserted over the wire. Acute dilatation using 16F Amplatz dilator was done. Then the sheath was inserted over the dilator.

In group A, the screwed Amplatz sheath was advanced by clockwise controlled rotation till the tip reached the collecting system (see Supplementary Fig. S1).

In group B the ordinary Amplatz sheath (Boston Scientific 16F) was used.

12F nephroscope with holmium laser disintegration was used in all patients. A nephrostomy tube and ureteric Double-J were inserted at the end of the procedure according to stone clearance and blood loss condition or other intraoperative hazards.

The operative time was calculated from ureteric catheter introduction till the end of the operation.

The fluoroscopy time was measured for each patient in both groups. All operative details were recorded and analyzed with special attention to the following points:

- Blood loss and the need for blood transfusion were done by calculation of maximal allowable blood loss in children.¹¹ Need for another needle puncture

- perforation and contrast extravasation

- Alken dilator overshooting or accesses sheath malposition as over migration or slipping outside the collecting system with a need for repositioning

- Need for nephrostomy tube insertion

- Stone-free rate and need for auxiliary procedures

Statistical analysis

The collected data were computerized and statistically analyzed using Statistical Package for the Social Sciences (SPSS) software version 27. To determine the distribution characteristics of variables and variance homogeneity, Kolmogorov–Smirnov and Levene tests were used. Descriptive statistics were calculated for all variables. Frequencies and percentages were used to reflect qualitative data. Mean and standard deviation was used to summarize quantitative results. A comparison between Group A and Group B was done using the appropriate tests of significance. Pearson's chi-squared test (χ ²), chi-square for linear trend, and Fisher exact test were used to compare categorical variables. An independent Student's t-test was used to compare continuous variables. A p-value <0.05 was considered statistically significant.

Results

Patient characteristics

Sixty-seven patients were divided randomly into two groups. Group A included 34 patients who underwent mini-perc in the supine position using a screwed sheath, while group B included 33 patients who underwent mini-perc in the supine position using a standard Amplatz sheath.

The mean age was 12.6 ± 2.45 years and 12.2 ± 2.33 years in groups A and B, respectively (see Supplementary Table S1).

Stone characteristics

The mean stone size was 15.5 ± 2.31 mm and 16.45 ± 3.21 mm in groups A and B, respectively.

The stone site was in lower calyx in 15 (44.1%) and 12 (36.4%) in group A and group B, respectively. While renal pelvis stones were 17 (50%) in group A and 18 (54.6%) in group B, middle calyx stones were 2 (5.9%) and 3 (9%) in group A and group B, respectively.

The mean stone density in group A was 915.4 ± 123.3 HU, while in group B, it was 890.2 ± 155.6 HU.

Intraoperative data

In the Table 1, there were no significant differences between both groups regarding puncture site and number.

Table 1.

Perioperative Data

	Group A	Group B	Test of significance	p
Number of puncture
Mean ± SD	1.1 ± 0.235	1.15 ± 0.315	t = 0.738
Range	1–2	1–2		0.463
Puncture site
Lower	30 (88.2%)	27 (81.8%)
Lower and middle	2 (5.9%)	3 (9.1%)	χ ² = 0.543	0.762
Middle	2 (5.9%)	3 (9.1%)
Operative time (minutes)
Mean ± SD	51.25 ± 2.15	52.35 ± 3.45	t = 1.571	0.121
Range	48–56	49–58
Fluoroscopy time (minutes)
Mean ± SD	2.1 ± 0.85	2.9 ± 1.05	t = 3.433	0.001
Range	1.8–2.5	2.4–3.6
Track loss/sheath repositioning
No	34 (100.0%)	27 (81.8%)	Fisher exact	0.0111
Yes	0 (0.00%)	6 (18.2%)
Bleeding need transfusion
No	33 (97.05%)	30 (90.9%)	χ ² = 1.282	0.288
Yes	1 (2.95%)	3 (9.1%)
Pelvicalyceal system perforation
No	33 (97.05%)	29 (87.8%)	χ ² = 2.043	0.153
Yes	1 (2.95%)	4 (12.2%)
Postoperative complication grade I and II
No	29 (85.3%)	27 (81.8%)	χ ² = 147	0.701
Yes	5 (14.7%)	6 (18.2%)
Stone free rate	94.11%	90.9%	χ ² = 0.249	0.617
Need for auxiliary procedure	5.89%	9.1%	χ ² = 0.249	0.617
Need to nephrostomy
No	20 (58.8%)	11 (33.3%)	χ ² = 4.376	0.036
Yes	14 (41.2%)	22 (66.7%)
Hospital stay (days)	1.2 ± 0.55	1.32 ± 0.08	t = 1.240	0.219

SD = standard deviation.

The mean operative time was 51.25 ± 2.15 minutes and 52.35 ± 3.45 minutes in groups A and B, respectively. It was lower in group A, but with a nonsignificant difference between both groups.

The fluoroscopy time was significantly lower in group A (2.1 ± 0.85 minutes) than in group B (2.9 ± 1.05 minutes).

Regarding track loss and sheath repositioning, group A showed no track loss in A while six cases (18.2%) were reported in group B, which were corrected easily due to the presence of a safety wire which facilitates repositioning of the sheath. Track loss was significantly lower in group A.

Perioperative complications

In Table 1, the bleeding necessitating blood transfusion was lower in group A as bleeding occurred in one patient (2.95%) and three patients (9.1%) in group B without a statistically significant difference p = 0.288.

The pelvicalyceal system perforation occurred in one patient (2.95%) in group A, and four patients (12.2%) in group B p = 0.153.

A significant difference regarding the need for a nephrostomy tube at the end of the procedures occurred in 14 patients (41.2%) in group A, while occurred in 22 patients (66.7%) in group B (P-0.036).

The postoperative complications were minor according to the modified Clavien grading system [28] and showed no significant difference between both groups reported, 14.7% and 18.2% in groups A and B, respectively.

Operative outcomes

The stone-free rate was 94.11% and 90.9% in group A and group B, respectively p = 0.617.

The need for the auxiliary procedure was lower in group A relative to group B, 5.89% and 9.1%, respectively, with insignificant differences p = 0.617.

Discussion

Mini PCNL had gained wide popularity since the nineties of the last century.¹² Dogan and his associates reported that PNL is a safe and effective treatment for pediatric renal stones.¹³

The main indications of mini PCNL are medium size stones with high density or small stones with the previous failure of extracorporeal shockwave lithotripsy.¹⁴

The wide spread of mini-perc all over the world was due to the use of the small instrument with a small diameter access sheath, which subsequently decreased morbidity in comparison to conventional PCNL.¹⁵

Also, Desai and his associates stated that both tract size and number are associated with increased intraoperative difficulties and complications, for example, bleeding during pediatric PCNL.¹⁶

Multipuncture or accesses mainly due to stone complexities, distributions,¹⁷ or as a result of flail tracts.¹⁸

Tract stability is the most important step in any percutaneous surgery. It decreases the need for sheath repositioning or develops a new track. A stable track also decreases blood loss, operative time, and fluoroscopy time.¹⁵

Abdominal wall thickness in adults is larger than in children,¹⁹ and it is around 3 and 7.5 cm in supine and prone positions, respectively.²⁰

Thinning of the pediatric abdominal wall may affect tract stability, but up to our knowledge, no study determined abdominal wall thickness in the supine position in this age group.

In pediatrics, the stability of the tract is expected to be lower than in adults. This was due to low pediatric abdominal wall thickness and even with thinned-out parenchyma patients. In our study, no cases reported having tract loss. This could be explained by the pitches of screwed Amplatz sheath giving mechanical fixation to the abdominal wall. This has prevented the problem of track loss and sheath migration either inside or outside the collecting system. So it decreased the need for sheath repositioning, especially in the supine position. It also decreased the burden on assistance to fix the sheath during nephroscope introduction and stone fragments retrieval,¹⁸ especially in pediatric-sized patients.

Pelvicalyceal system perforation and extravasation were reported in one patient within group A (2.4%); it was lower but not statistically significant than group B utilized ordinary sheath. It was also lower than Desoky et al in their work in mini-perc in supine position children²¹ and also lower than Kumar and Anand with their associates taking into consideration the difference in their stone size or location.²² This could be explained by the controlled clockwise advancement of the screwed sheath that prevents assembly overshooting. Also, it can be explained by the stability of the screwed sheath with its nut. Previously mentioned advantages of the screwed sheath could be a complementary factor to our case selection in that low incidence.

PCNL is a challenging procedure in the pediatric population because of the small kidney and the low tolerance to blood loss. The use of the mini-PCNL technique is becoming increasingly popular in the treatment of kidney stones in pediatric patients. In our current work, there was a nonstatistically significant lower incidence of screwed sheath users. Regarding intraoperative bleeding necessitating blood transfusion, both screwed and nonscrewed sheath groups showed hemoglobin drop within the same range of many kinds of literature (0.4%–24%),^21,23 our numerically lower figures for group A could be explained by lower needs for sheaths remanipulation.

According to the Clavien grading system,²⁴ our postoperative complications were minor and graded as grades I and II. The results of our current study were comparable to a study done by Elderwy et al who reported 8.5%²⁵ and lower than another study done by Onal et al who reported 23.04%.¹⁷

The operative time in our study was calculated from ureteric catheter insertion till nephrostomy tube fixation and this match with many authors such as De Sio et al.²⁶

Other studies such as Baseri calculate from induction of anesthesia to nephrostomy tube fixation.²⁷

Although screwed sheath users' operative time was lower than ordinary sheath users with no significant difference, both the screwed sheath group (55 minutes) and ordinary sheath group (62 minutes) have mean operative times, less than a study done by Desoky et al who reported 65.1 minutes during their mini-perc in the supine position in children.²¹

Low-dose pediatric radiation exposure is crucial. It was the trigger for Penbegu et al in their study to use ultrasound-guided punctures in children.²⁸ Our mean fluoroscopy time was low. The mean of fluoroscopy time was in group A (2.41 ± 0.94 minutes), which is significantly lower than group B (2.80 ± 0.741 minutes). The decrease in fluoroscopy time in screwed sheath users was attributed to a stable tract with fewer needs for C-arm guidance to resume our procedure. Also, our data regarding radiation exposure were lower than in many other studies.^21,29,30

The success of the procedure is considered if the stone is completely removed or residual fragments are <4 mm.³⁰

The stone-free rate was higher but not statistically significant in screwed sheath users (94.11%) than in ordinary sheath users (90.9%). Our results were comparable to Zeng and Desoky with their colleagues in their pediatric work^21,29,30 and also higher than Ozden and Resorlu with their colleagues.^30,31

Tubeless procedures are done when there are no residual stones, no hood of a second look, and without intraoperative bleeding or urine extravasation.³²

In our study, tubeless procedure was reported in (58.8%) of screwed sheath users and (33.3%) in ordinary sheath users, that significant difference could be explained by our data regarding intraoperative bleeding, perforation, sheath reposition, and stone residual state.

Limitation

This is the initial study about the value of the screwed sheath in pediatric mini-perc surgery, so the main limitation facing us was the lack of research for a comparison of the outcomes of the procedure.

Expected advantages or disadvantages could be elucidated when a larger scale of patients is included and with using the sheath in different stone demographics and complexities.

Conclusion

Screwed sheaths enable the urologist to have a stable track during pediatric mini-perc surgery, especially in the supine position and overcoming the pediatric thin abdominal wall. The screw sheath provides significantly lower fluoroscopy time and decreases the need for nephrostomy tube insertion when compared with ordinary sheath in mini-perc renal surgery.

Footnotes

Authors' Contributions

K.A.: protocol development, data collection, and article writing. D.E.: protocol development, data collection, and article writing. E.R.E.: article writing and data analysis. Mahmoud M. Malek: data collection. M.M.S.: protocol development, data collection, and article writing.

Patient Consent

This study includes human patients with renal stones. Every patient consented after detailed information about the study.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Supplementary Material

Supplementary Figure S1

Supplementary Table S1

Abbreviations Used

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