Comparison of Mini-Percutaneous Nephrolithotomy by Standard and Miniperc Instruments in Pediatric Population: A Single-Center Experience.

OBJECTIVE: The objective of this study was to compare mini-percutaneous nephrolithotomy (PCNL) performed by standard and Miniperc techniques in pediatric patients.
MATERIALS AND METHODS: This was a retrospective study conducted at our institution between January 2012 and December 2017. The outcomes of pediatric renal stones treated by mini-PCNL done by Miniperc and standard techniques were compared in terms of the drop in the hemoglobin, stone-free rate, and analgesic requirement in the first 24 h.
RESULTS: A total of 57 children (age: 1-16 years), who underwent mini-PCNL by Miniperc equipment (n = 23) and standard equipment (n = 34), were included in this study. The postoperative mean drop in hemoglobin was significantly higher in mini-PCNL done by standard compared to the Miniperc technique. The stone-free rate was 95.65% in the Miniperc group and 94.12% in the standard mini-PCNL group. The need for analgesics was significantly lower in the Miniperc group compared to the standard mini-PCNL group (P = 0.0002). In the Miniperc group, the majority of the patients required only one dose of analgesics, whereas, in the standard mini-PCNL group, around 44% of the patients required three or more than three doses of analgesics to reduce postoperative pain.
CONCLUSION: Both the techniques were safe and efficacious in the management of pediatric renal stone and stone clearance. However, the Miniperc technique resulted in significantly less pain and a lower dosage of analgesics. Copyright:

INTRODUCTION

The incidence of urolithiasis in the pediatric population is increasing worldwide and estimated to be 1 in 10,000 children.[1] In addition, the prevalence rate is higher in developing countries compared to developed countries.[2] Percutaneous endoscopic management of renal stones is undergoing continuous improvement with the advent of newer endoscopes. Percutaneous nephrolithotomy (PCNL) is a standard procedure used to treat large stone volume, but it is associated with more complications. The availability of newer, smaller endoscopes has benefitted pediatric stone disease management significantly. There is evidence that the reduction of tract size leads to a lower number of complications in percutaneous surgery.[3] Complete stone clearance is required to prevent infections and stone recurrence. While achieving this aim, it is also necessary to use the smallest endoscope, which causes less damage to the kidney parenchyma and has comparable results with the standard procedure. This can be achieved with recently available minimally invasive percutaneous nephrolithotomy (Miniperc) technique, especially for children having less space in the pelvicalyceal system. The data reported by Celik et al. indicate that although the stone-free rates were comparable between standard PCNL, mini-PCNL, and ultra-mini-PCNL technique, the chances of bleeding were significantly less with the ultra-mini-PCNL group, having the smallest tract size of 9.5 F.[4] The term mini-PCNL refers to tract size between 14 F and 20 F. Various endoscopes and instruments are designed to fit into this category. Most of the studies of pediatric PCNL are done using adult-sized instruments. In our study, we have used smaller caliber instruments for pediatric PCNLs. To assess the effectiveness of smaller available endoscopes, the present study aimed to compare mini-PCNL performed using standard instruments and Miniperc instruments in the management of pediatric renal stones.

MATERIALS AND METHODS

This was a retrospective study conducted at our institution between January 2012 and December 2017. Pediatric patients (age: 1–16 years) who underwent mini-PCNL for renal stones using Miniperc and standard instruments were included in this study. All the procedures were performed by a single urologist (ADM). Ethics committee approval was obtained from our hospital ethics committee, and informed consent was obtained from the parents.

Demographic characteristics including age, sex, and size and number of stones were noted. Stone size ranged from 9 mm to 30 mm. Stones were either solitary, partial staghorn, or multiple. All patients were preoperatively evaluated with complete blood count, creatinine, urine culture, sonography, and intravenous urography. Computed tomography (CT) scan was performed only in low-density or radiolucent stones. Around 10% of the patients had radiolucent stones.

Pediatric patients with stones with sizes in the range of 1–2 cm were given an option of choosing between shock wave lithotripsy (SWL) and mini-PCNL. Parents who chose mini-PCNL for their children were included in the study. All patients having renal stones > 2 cm in size and solitary or multiple calyceal stones were offered mini-PCNL as the primary procedure. Renal stones more than 4 cm in size (especially staghorn stones with complex anatomy) and patients without nephrostomy and double J (DJ) stent after the procedure were excluded from the study protocol.

Mini-PCNL procedures were performed either using a standard 18 F nephroscope (Karl Storz) through a 20 F Amplatz sheath or by Miniperc procedures performed using 12 F nephroscope through a 16.5 F sheath (MIP M, Karl Storz). The case selection was random for both the procedures.

The surgery was performed after proper antibiotic cover and sterile urine culture. All the procedures were done under general anesthesia. Prior cystoscopy and placement of ureteric catheter of appropriate size were done using a 7.5 F pediatric cystoscope or 8/9.8 F ureteroscope. All the procedures were performed in a prone position. Access to the pelvicalyceal system was obtained under fluoroscopic guidance using the bullseye technique. In the standard mini-PCNL group, the tract was dilated by an Amplatz dilator and a 20 F Amplatz sheath was placed. 18 F nephroscope was used, and the stones were fragmented with either pneumatic lithotripter or laser lithotripsy. Fragments were extracted with forceps. In the Miniperc group, single-step dilatation was performed and a 16.5/17.5 F metal sheath was placed. The stone was fragmented by holmium laser lithotripsy. Stones were evacuated by vacuum cleaner effect. At the end of the procedure, systematic visualization of the complete pelvicalyceal system was done by the nephroscope to confirm the removal of all stone fragments. Fluoroscopic confirmation was done at the end of the procedure for stone clearance, and a DJ stent was placed. A 14 F nephrostomy was placed in all the patients. Per-urethral catheter and nephrostomy were removed when clinically indicated, usually at 48 h, and the patients were discharged. An X-ray kidney, ureter, and bladder (KUB) was done just before removal of nephrostomy to confirm that there were no large residual fragments, needing second-look nephroscopy. A repeat X-ray KUB and ultrasonography were done after 2 weeks, and the stent was then removed after documentation of stone-free status. A plain CT scan was not done due to the limitation of cost and risk of radiation exposure to pediatric patients. All DJ stents were removed under short general anesthesia.

All patients underwent complete blood count before and postsurgery at 24 h to assess the drop in the hemoglobin level. Postoperative complications were classified according to the modified Clavien–Dindo classification. The need and number of doses of intravenous analgesia within the first 24 h of surgery were recorded. We presumed that the severity of pain roughly correlated with the number of analgesic doses needed. Each dose comprised 1 cc of diluted 10 mL solution of pentazocine with promethazine prepared with the appropriate dose depending on the child's weight. The anesthesiologist prepared this solution immediately after surgery. As the evaluation of pain score was not possible in children, the analgesic dose was administered on the complaint of pain in older children and excessive crying in smaller children. Analgesic doses were administered only on demand.

All statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS), version 20.0, IBM, Chicago, USA. The qualitative data were expressed as number and percentage, whereas the quantitative data were expressed as mean and standard deviation. A unpaired t-test was applied to check the significant difference between the two groups, and a paired t-test was applied to check the significant difference between pre- and postoperative results. Statistical significance was defined as P < 0.05.

RESULTS

A total of 57 pediatric patients, who underwent mini-PCNL with Miniperc instruments (n = 23) and standard instruments (n = 34), were included in this study. Table 1 shows that the demographic characteristics of the patients in the two groups were comparable. The mean age of the patients was 8.21 years in the Miniperc and 9.96 years in the standard mini-PCNL group. The mean stone size for the Miniperc and standard mini-PCNL groups was comparable (18.4 and 17.9 mm, respectively). The operative time in the standard mini-PCNL group was marginally longer than the Miniperc group (48 min vs. 35 min). The operative time was calculated from the initiation of puncture till the placement of a nephrostomy tube.

Table 1

Demographic profile of patients

Characteristics	Miniperc (n=23)	Std M-PCNL (n=34)	P
Age (years), mean (SD)	8.21 (2.81)	9.96 (4.03)	0.076
Sex
Male	15 (65.21)	26 (76.47)	0.343
Female	8 (34.78)	8 (23.53)
Side of stone
Right	14 (60.86)	21 (61.76)	0.946
Left	09 (39.13)	13 (38.23)
Stone size (mm), mean (SD)	18.43 (7.29)	17.96 (7.84)	0.820
Operative time (min), mean (SD)	35 (10.2)	48 (12.6)	0.0001

Data shown as n (%), unless otherwise specified. Miniperc, minimally invasive percutaneous nephrolithotomy; Std M-PCNL: Standard mini-percutaneous nephrolithotomy, SD: Standard deviation

Of the 57 patients, 39 were lower calyceal punctures, 11 were mid-calyceal punctures, and 7 were supracostal upper calyx puncture above the 12th rib. Out of the 7 supracostal punctures, 4 were from the standard mini-PCNL group and 3 from the Miniperc group. None of the patients with supracostal access required a thoracic drain after the procedure. There was no injury to contiguous organs during the puncture or tract dilatation in both the groups. One child from the standard mini-PCNL group had a small pelvic injury during tract dilatation leading to extravasation of irrigation fluid in the peritoneal cavity. This was recognized immediately at the end of the procedure due to a distended abdomen. Sonography confirmed it, and small ultrasonography-guided peritoneal drain was kept for 4 days and later removed. The child had an uneventful recovery.

None of the patients in either group had any major intraoperative or postoperative bleeding requiring transfusion, angio-embolization, or two-stage procedure. The drop in the hemoglobin was evaluated in both the groups. The mean difference in the pre- and postoperative hemoglobin was 1.31 in the standard mini-PCNL group and 0.57 in the Miniperc group. The overall drop in hemoglobin (preoperative to postoperative) was significantly higher (P = 0.0004) in the standard mini-PCNL group than in the Miniperc group (P = 0.189) [Table 2].

Table 2

Comparison of levels of hemoglobin between Miniperc and percutaneous nephrolithotomy

Hemoglobin (mg/dL)	Miniperc (n=23)	Std M-PCNL (n=34)	P *
Preoperative	12.11 (1.63)	11.48 (1.67)	0.162
Postoperative	11.54 (1.24)	10.17 (1.19)	0.052
Drop (mean difference)	0.57	1.31	-
P**	0.189	0.0004	-

Data shown as mean (SD). Miniperc, minimally invasive percutaneous nephrolithotomy; Std M-PCNL: Standard mini-percutaneous nephrolithotomy, *Comparison between Miniperc and Std M-PCNL, **Comparison between preoperative and postoperative data. SD: Standard deviation

The stone-free rate was 95.65% in the Miniperc group and 94.12% in the standard mini-PCNL group. Although there is no consensus on the size of clinically insignificant residual fragments, we considered stone size >4 mm as a significant residual fragment. Total three patients had clinically significant residual fragments. No patients required secondary ancillary procedures like SWL or second-look PCNL.

Postoperative complication was categorized according to the modified Clavien–Dindo classification. Grade I injury was present in four patients in the Miniperc group and six patients in the standard mini-PCNL group. There were no patients in Grade II, IV, or V complication. One patient had Grade III complication in the standard mini-PCNL group [Table 3]. Postoperative pain was separately documented.

Table 3

Postoperative data

Parameters	Miniperc (n=23), n (%)	Std M-PCNL (n=34), n (%)	P
Stone-free rate	22 (95.65)	32 (94.12)	0.80
Modified Clavien-Dindo classification
Grade I	4 (17.39)	6 (17.65)	0.980
Grade II	0	0	-
Grade III	0	1	-
Need for analgesics in the first 24 h	15 (65.21)	34 (100)	0.002
1 dose	8 (53.33)	6 (17.64)
2 doses	5 (33.33)	13 (38.23)
≥3 doses	2 (13.33%)	15 (44.11%)

Data shown as n (%). Miniperc, minimally invasive percutaneous nephrolithotomy; Std M-PCNL: Standard mini-percutaneous nephrolithotomy

For assessment of pain postoperatively, the need for analgesics within the first 24 h was evaluated. Analgesics were administered when there was excessive crying by the child or when elder children complained of pain at the operated site [Table 3]. The need for analgesics was significantly lower in the Miniperc compared to the standard mini-PCNL group (P = 0.002). Of the 15 patients requiring analgesic dosages from the Miniperc group, 8 required only one dose, 5 required two doses, and 2 required three or more doses of analgesics within 24 h after surgery. However, in the standard mini-PCNL group, all the children required analgesics. Overall, 6, 13, and 15 children required only one dose, two doses, and three or more doses of analgesics within 24 h postoperatively.

All the patients were followed up for a period of 1–5 years to look for recurrence of stone disease.

DISCUSSION

When managing stones in pediatric patients, we need to focus on achieving a complete stone clearance rate with minimal morbidity. As stone recurrence is observed frequently in children, endoscopic treatment is preferred over open surgery because repeat procedures can be done with acceptable morbidity, if required.[5] For the treatment of renal stones in children, SWL is recommended as the first-line modality by European guidelines.[6] Although SWL can be offered to children with smaller stones, it requires general anesthesia, sometimes multiple sessions, and chances of renal injury.[5]

PCNL has gained popularity in pediatric patients since it was first reported by Woodside et al.[7] PCNL is now an established procedure in children and is a procedure of choice for renal stones of size more than 2 cm. Many studies have proved the safety and efficacy of PCNL in pediatric patients, but most of these studies are performed with adult-size instruments.[8910] Kapoor et al. used an adult-size sheath from 24 to 30 Fr in children and achieved a stone-free rate of 74.2% in a single session, which improved to 83.9% after the second procedure.[8] Yadav et al. also used adult-size instruments in 639 pediatric patients and achieved a 94.39% stone-free rate with a 0.45% major complication rate.[9] The stone-free rates of standard M-PCNL in the present study are comparable with these studies.

The main concern of PCNL in pediatric patients is bleeding due to the use of adult instruments in the small pediatric pelvicalyceal system.[11] Although there is no direct evidence that a smaller tract will lead to reduce bleeding, newer smaller caliber endoscopes have been introduced with an aim to prevent renal parenchymal damage. This led to the use of smaller instruments for pediatric endoscopic renal percutaneous procedures.

Various studies compared the use of miniaturized endoscope in pediatric patients. Jones et al. reviewed the results obtained with the use of microperc and ultra-Miniperc in pediatric patients and concluded that larger tract size resulted in higher complication rates in terms of hematuria and extravasation.[12] Celik et al. compared the results of pediatric PCNL using adult-sized, Miniperc-PCNL, and ultra-mini-PCNL done in 225 renal units.[4] They concluded that although the stone-free rates were almost similar in all the three groups, the drop in mean hematocrit was significantly lesser in the ultra-mini-PCNL group, suggesting that reduced tract dilatation and smaller caliber nephroscope result in fewer complications. A multicenter study performed by Guven et al. included three different centers, wherein one center performed PCNL using a pediatric endoscope, and the other two used adult nephroscope for PCNL. They concluded that the drop in the hemoglobin was less at the center where pediatric instruments were used.[13] Our results were comparable to this study although ours is a single-center experience.

With the introduction of Miniperc instruments, there was a renewed interest in performing mini-PCNL with these endoscopes. As the sheath size is smaller, there is a special advantage of using these instruments in pediatric patients. Wah et al. reported their initial experience of Miniperc in 23 patients and concluded that it is a safe and effective procedure for the management of renal stones in children.[14]

Manohar et al. used a slender 18 F nephroscope and achieved an 86% stone clearance rate in complex staghorn calculus in children <5 years of age.[15] Recently, Galal et al. presented their experience of Miniperc in pediatric patients and suggested that Miniperc can be safely performed in children with adequate safety and with no blood loss or major complications.[16] Bodakci et al. performed mini-PCNL in infants <3 years of age and concluded that although it has higher stone-free rates, shorter hospital stay, and excellent esthetic outcomes, there is a higher incidence of surgical hypothermia and radiation in these children.[17]

It is still not clear whether reducing the tract size reduces the pain. Insertion of the nephrostomy was considered as the primary cause; hence, tubeless procedures were performed to reduce the pain after PCNL or Miniperc. Knoll et al. showed that tubeless Miniperc had a lower pain score as compared to the PCNL with nephrostomy.[18] The study by Kukreja suggests that although PCNL with nephrostomy had a higher pain score, the tubeless procedure performed by PCNL or Miniperc had no difference in pain score. They concluded that reducing the tract size is not associated with a reduction in pain score, but tubeless procedure (either PCNL or Miniperc) causes less postoperative pain. As blood loss was significantly less with Miniperc, it was suggested that Miniperc should be the ideal tract for stones in the size range of 15–30 mm for all patients.[19] To negate the effect of the nephrostomy tube size, we placed the same size nephrostomy tube in all patients and have excluded tubeless PCNLs from this study.

To our knowledge, no single-center study has compared mini-PCNL with standard and Miniperc instruments in pediatric patients. We assessed the effectiveness of Miniperc over standard mini-PCNL instruments in terms of drop in hemoglobin, stone-free rate, and need for analgesics. It was observed that the drop in the hemoglobin was significantly less in the Miniperc group compared to mini-PCNL done with standard instruments. This may be attributed to reduced tract size of Miniperc.

In the present study, the immediate postoperative stone-free rate was 95.65% and 94.12% in the Miniperc and standard mini-PCNL groups, respectively. Although the difference was not statistically significant, the stone-free rate was comparatively greater in the Miniperc than the standard mini-PCNL group. All the residual stones were of the size <3 mm, so the overall stone-free rate was 100%.

To the best of our knowledge, this is the only study that assessed the analgesic dosage requirement after mini-PCNL done using Miniperc or standard PCNL instruments in the pediatric population. Although previous studies have reported analgesic requirements, they did not mention the number of dosages required.[20] The present study compared both the groups in terms of requiring no analgesic or requiring one, two, or more than three doses of analgesics in the first 24 h after the surgery. The number of patients who required analgesics was significantly less in the Miniperc group. In addition, the number of doses required was higher in the standard mini-PCNL group than in the Miniperc group. These findings support the general understanding that postoperative pain depends on the tract size. The use of miniaturized tract size helps to reduce postoperative pain with lesser requirement of analgesics.

The present study had a few limitations. Ultrasonography and X-ray KUB were used to assess the stone-free rate. CT scan was not done due to the cost and risk of exposure of radiation to children. This could have affected the exact incidence of stone-free rate. Pain scores were not used for evaluation, as it was difficult to administer such scores in smaller children. As analgesics were administered on-demand basis, it might have altered the results for children having higher pain tolerance.

CONCLUSION

Mini-PCNL performed using Miniperc technique was associated with a significantly less drop in the hemoglobin and resulted in a slightly better stone-free rate as compared to standard mini-PCNL technique in the pediatric population. Further, the number of patients requiring analgesics was significantly lower in the Miniperc group compared to the standard mini-PCNL group, suggesting less postoperative pain.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.