Stone Clearance Rate and Postoperative Recovery of Mini Percutaneous Nephrolithotomy: A Single-Institute Study : Journal of Marine Medical Society

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Stone Clearance Rate and Postoperative Recovery of Mini Percutaneous Nephrolithotomy: A Single-Institute Study

Shah, Amit Kumar Col1; Upadhye, Manoj A Maj2; Deepak, H Maj2,; Goud, Naveen Kumar Surg Lt Cdr2; Shah, Akshat Mr3

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Journal of Marine Medical Society 25(1):p 10-15, Jan–Jun 2023. | DOI: 10.4103/jmms.jmms_66_21
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Urolithiasis has been one of the most common urological diseases of humankind since ancient times affecting a large global population. Between 1% and 15% of the world population are affected by the disease at some point in their life. Despite the innate knowledge and extensive research, the incidence of the disease is on the rise due to multiple factors including improper diet, sedentary lifestyle, and reduced hydration in arid areas of the globe.

Percutaneous nephrolithotomy (PCNL) has now largely replaced open surgery as a safe and effective treatment for renal stones.[1] The “Guy’s Stone Score” proposed by Thomas K and Smith et al.[2,3] is a valuable tool to stratify the complexity of PCNL procedures into four groups based on the stone burden and the anatomy of both patient and renal tract. During the last two decades, the evaluation and management of kidney stones have vastly altered. The era of open surgery has long been forgotten in the field of Urology and with the advent of smaller caliber nephroscopes, conventional PCNL is giving way to Mini Perc and micro PCNL. With higher cost of extra corporeal shockwave lithotripsy (ESWL) machines and flexible ureteroscopes, in addition to larger stones, now, Mini Perc is even being adjudged a better feasible procedure for clearance of stones ranging between 1 cm and 1.5 cm.[4] Such stones ideally would undergo ESWL or retrograde intrarenal surgery (RIRS), being lesser invasive as compared to Mini Perc.

However, there have been rapid rise, progressive alterations, and continued technological advancements of procedures such as Mini Perc, Micro Perc, and Ultra Mini Perc despite the existence of conventional ESWL and recently introduced RIRS procedures which are considered to be less invasive. The reason for the above can be attributable to the fact that these procedures are more cost-effective and have better stone clearance rate with a smaller caliber tract providing more satisfactory outcomes along with being minimally invasive.


Patients who underwent Mini Perc at the tertiary care center for the management of kidney stones at its department of urology were vetted against the criteria for inclusion and exclusion. A total of 78 patients who met the inclusion criteria were selected out of the total enrolled 124 patients. Mini Perc was done as per on-going practice guidelines, where after a successful puncture of Pelvicalyceal system (PCS), the track was dilated till 18 Fr over a guide and standard 16 Fr nephroscope were used. Holmium Laser with 200 and 365μ fiber or/in combination of ultrasonic probe 5.7 Fr or 2.4 Fr combined probe of Swiss Master/EMS Dual Lithoclast® was used as an energy source for stone clearance. The study is summarized in Figure 1.

Figure 1:
Flow Chart for study design

Inclusion criteria

All adult patients who underwent Mini Perc in clinically and radiologically proven renal calculi registered at the outpatient department of the tertiary care hospital.

Exclusion criteria

Pediatric age patients

Postoperative recovery assessments were done by:

  • A) Modified Clavien–Dindo System,[5] which is stratified into five grades:
    • Grade 1: Any deviation from the normal postoperative course without the need for pharmacologic treatment or surgical, endoscopic, and radiologic interventions. Allowed therapeutic regimens include drugs such as antiemetics, antipyretics, analgesics, diuretics, electrolytes, and physiotherapy.
    • Grade 2: Complications requiring pharmacologic treatment with drugs other than allowed for Grade 1 complications. Blood transfusions and total parenteral nutrition are also included.
    • Grade 3a: Intervention not under general anesthesia Grade 3b: Intervention under general anesthesia
    • Grade 4: Life-threatening complications, urosepsis (including central nervous system complications) requiring intensive care unit stay
      • Grade 4a: Single-organ dysfunction (including dialysis)
      • Grade 4b: Multi-organ dysfunction
    • Grade 5: Death of the patient.
  • B) Visual analog score for assessment of pain at the puncture site and abdominal pain postoperatively, as depicted in Figure 2.
  • C) Evaluation of postoperative stone clearance: Postoperative stone clearance is defined as complete absence or presence of residual stone ≤4 mm in dimension on ultrasonography (USG) kidney, ureter, and bladder (KUB) performed after 1 month from the day of surgery.

Figure 2:
Visual analogue scale

All patients had antegrade DJ stenting (DJS) done as a prophylaxis to prevent obstruction/postoperative urinary leak, 34 patients had tubeless Mini Perc (without nephrostomy), and 44 patients had 14 Fr nephrostomy which was removed on 1st or 2nd postoperative day. All D JS were removed between 2 and 4 weeks.

Statistical analysis

Quantitative data had been presented with help of mean and standard deviation. The qualitative data were being presented with help of the frequency and percentage table.

Results were represented as graphs wherever required. The statistical software MS Excel (MS Office Professional 2019), SPSS ver. 20 (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY, USA: IBM Corp.), was used.


The patient’s characteristics and demographics are summarized in Table 1. The majority of the patients, 26 (33.32%), were from the age group of 31–40 years followed by 15 (19.22%) from the age group of 41–50 years, 13 (16.67%) from the age group of 21–30 years, 11 (14.1%) from the age group of 61–70 years, 7 (8.98%) from the age group of 51–60 years, 4 (5.3%) from the age group of 71–80 years, and 2 (2.57%) from the age group of 11–20 years. The mean age of patients was 43.37 ± 14.603 years. Thirty-one (39.76%) patients had body mass index (BMI) in the normal range, while 32 (41.02%) and 14 (17.98%) patients were overweight and obese, respectively. The mean BMI of patients was 26.52 ± 4.872 kg/m2. About 38.46% of the patients were hypertensive, while 24.34% were diabetic and 5.13% of patients suffered from chronic obstructive pulmonary disease, 3.82% from hypothyroidism, and one patient of polycystic ovarian disease. Patients of both genders were taken out of which 60.24% were males and the rest were females contributing to 39.76% of the population.

Tabel 1:
Patient characteristics and Demographics

Preoperative computed tomography (CT)–intravenous urography was done to delineate the anatomical relation of stone with renal parenchyma. The distribution of stone is described in Table 2.

Table 2:
Stone Parameters

Twenty-seven patients had stones detected in the lower pole with a mean dimension of 20 mm (12–27), 21 patients had stones detected in the upper pole with a mean dimension of 14 mm (11–18), 19 remaining patients had stones in the middle calyceal region with a mean dimension of 18 mm (14–25), and 11 patients had stones detected in the pelvic region with a mean dimension of 31 mm (19–37).

Description of stone burden as per Guy’s Stone Grade is summarized in Table 3. According to Guy’s Stone system, Grade I, II, and III were 46, 21, and 11 patients, respectively.

Table 3:
Stone burden as per Guy’s Stone Score

Postoperative stone clearance is defined as complete absence or presence of residual stone ≤4 mm in dimension on USG KUB performed after 1 month from the day of surgery.[6]

In 78 patients who underwent Mini Perc, stone clearance was detected in 75 (96.15%) patients and residual stone in 3 (3.85%) patients. Out of the three patients with residual stones, two of them had residual stone fragments of 7 mm and 9 mm which was managed with ESWL and the last patient had residual fragment stone of 5 mm who was followed up and reported no complications. Graphical representation of the stone clearance is depicted in Figure 3.

Figure 3:
Stone clearance rate

Distribution of patients according to Modified Clavien–Dindo grade is summarized in Figure 4.

Figure 4:
Distribution according to modified clavien dindo grade

Among the complications, the most commonly noted one was fever recorded in 12 (15.38%) patients followed by bleeding at the surgical site in 3 (3.84%) patients. Sepsis was noted in 2 (2.56%) patients and pleural injury in01 (1.28) patient. Hemorrhage requiring intervention was recorded in 1 (1.28%) of patients. This patient had profuse bleeding up to postoperative day 3, required CT angiography with superselective embolization under general anesthesia to control the bleeding, and required intensive care for 6 days following intervention before complete recovery. Postoperative urinary leak from the nephrostomy site was not recorded in any of the patients who were included in our study. This could be attributable to the placement of DJ stent as a mandatory procedure in all. No mortality was recorded in our study. The summary of results is depicted in Table 4. The relationship of Guy’s Stone Grade with the Modified Clavien–Dindo complication system is described in Table 5.

Tabel 4:
Summary of results
Table 5:
Relationship between Guy’s Stone Grade and Modified Clavien Dindo Grade

Serial evaluation of pain assessment was done at 6th, 12th, 24th, and 48th h intervals from the time of recovery from anesthesia. Assessment was carried out based on a visual analog scale. It is evident from the observation and statistical analysis that the pain intensity declined as the time progressed from the surgery.


The AUA nephrolithiasis guidelines panel on renal calculi[7] has laid down recent protocols for the management of pelvicalyceal stones. Beginning from the history and advent of surgical intervention for the treatment of renal pelvicalyceal stones, Wickham and Kellett[8] in 1981 published their conclusions that small mobile calculus in the renal pelvicalyceal collecting system can be extracted through a percutaneous tract. Subsequent studies proposed PCNL as a routine technique to treat patients with large complex calculi.[9,10] Advances in technology of using energy for stone dissolution and surgical technique and practices assisted the urologist to extract calculi percutaneously with increasing efficiency and the first report of the percutaneous surgical management of staghorn calculus was by Clayman et al. in 1983.[11]

Since then, many research reports have been published describing surgical management of renal pelvicalyceal stones calculi.[12–14] Improved PCNL techniques, incorporating the increasing use of flexible nephroscopy and providing complete or near complete stone clearance at the time of the primary procedure have over a period of time has eliminated the need for secondary or any additional ESWL treatment.[15]

The prime objective in PCNL is complete stone clearance with minimum morbidity and mortality. For the past three decades, PCNL has been used as a primary modality of management for pelvicalyceal calculi to achieve that objective. The procedure has been altered, changed, and improvised over the technique described by Wickham and Kellett.[8] The most recent of these has been a paradigm shift in energy sources for vaporizing the stones rather than breaking them with the usage of LASER and ultrasonic energy; in addition, the decreasing caliber of nephroscope with improved vision and even incorporation of flexible scopes has helped stone clearance rate to be reported as complete.[16,17] The AUA nephrolithiasis guidelines panel on renal calculi[7] suggested that percutaneous monotherapy is associated with a 79% stone clearance rate, acute complication rates of 15%, and transfusion rates of 18%. It is evident from the above analysis is that the stone clearance rate has improved with a decrease in associated complications and morbidity (fewer complications and blood loss), as our experience increased.

While addressing the intraoperative technique and skill aspects, during the surgical procedure, the renal pelvicalyceal system access is achieved by the operating urologists under the guidance of fluoroscopy, ultrasound, or both. Familiarization with the renal pelvicalyceal anatomy and the relative position of the stone in it is mandatory for obtaining satisfactory results. Assessment of preoperative images of anteroposterior and lateral plain X-rays and CT urography was done with 3D reconstruction which proved to be very useful in planning the percutaneous access.

The stone clearance rate observed in our study is 96.15% which is incongruity with the studies which were conducted in the past. Malcolm et al.[18] retrospectively evaluated and published their experience with tubeless PCNL to evaluate its safety and efficacy for 42 cases of complex renal calculi, including 25 total/partial staghorn stones, and reported a single procedure stone-free rate of 74.5%, and a two-procedure stone-free rate of 91.5%. The research concluded that PCNL is safe and effective and can be used as a primary modality of management in cases of complex renal stone disease.

Similarly, few other studies conducted in the past decade such as Shahet al., Guptaet al., and Karaet al.[19–21] arrived at a similar conclusion of stone-free clearance achieved in patients ranging from 85% to 94%.

In our study, the postoperative complications were observed assessed and recorded as per the Modified Clavien–Dindo grading. Out of 78 patients evaluated, 12 presented with postoperative fever, 3 patients with postoperative bleeding at the operative site, and 1 patient with an injury to the pleura which were recorded as Grade I (20.51%) and managed conservatively. Two patients were diagnosed with postoperative sepsis, which was recorded as Grade II (2.56%) and managed accordingly and 1 patient who was graded as Grade IIIB (1.2%) had profuse bleeding up to postoperative day 3 which required CT Angiography with superselective embolization under general anesthesia to control the bleeding and required intensive care for 6 days following intervention before complete recovery. No mortality was recorded in our study. Summary of the results is depicted In Table 4. Other related complications such as organ injury such as liver injury and splenic injury and pulmonary complications such as pneumothorax, hydrothorax, hemothorax, colonic injury, and renoplueral fistula were not seen in any of the cases. Similar studies done in the past such as Grosso et al. and Nikic et al.[22,23] have arrived at the results which are in consistent with the above findings.

Serial evaluation of pain assessment was done at 6th, 12th, 24th, and 48th intervals from the time of recovery from anesthesia. The assessment was carried out based on a visual analog scale.

Patients had mild-to-moderate pain at the PCN site for 1–2 days, the severity of pain was managed adequately by analgesics. Injectin tramadol hydrochloride 50 mg twice daily was used in all patients for 2 days postoperatively and as and when required thereafter. There was no statistically significant increased chest pain or respiratory-related incidences. It is evident from the observation and statistical analysis that the pain intensity declined as the time progressed from the time of recovery from anesthesia. Postoperative pain assessment and validation study conducted by Haghighi et al.[13] has come to similar conclusions comparable with our study.


PCNL has been accepted to play an important role in management of complex and large calculi in upper renal tract. Most important challenge for an operating surgeon is to gain access to renal pelvis through the percutaneous route. Familiarity in using a proper updated equipment, improved miniaturized instruments, and practicing standardized protocol and technique can help surgeons to achieve excellent stone-free results with minimal patient morbidity. Hence, there has been exponential rise of procedures such as Mini Perc, Micro Perc, and Ultra Mini Perc as an added armory in urologist’s armamentarium.

The Modified Clavien–Dindo system of grading for perioperative complications is easy to use and reproducible. It can be used as an objective and reliable method for describing the complications associated with PCNL or Mini Perc and help in stratifying cases between surgeons of different experiences and reporting results.

Postoperative complications with respect to Mini Perc procedure are within acceptable parameters when weighted against its outcome in terms of stone clearance and postoperative pain management.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


1. Desai M, Sun Y, Buchholz N, Fuller A, Matsuda T, Matlaga B, et al. Treatment selection for urolithiasis:Percutaneous nephrolithomy, ureteroscopy, shock wave lithotripsy, and active monitoring. World J Urol 2017;35:1395–9.
2. Thomas K, Smith NC, Hegarty N, Glass JM. The Guy's stone score—grading the complexity of percutaneous nephrolithotomy procedures. Urology 2011;78:277–81.
3. Thomas K, Smith NC, Hegarty N, Glass JM. The guy's stone score-grading the complexity of percutaneous nephrolithotomy procedures. Urology 2011;78:277–81.
4. Lahme S, Zimmermanns V, Hochmuth A, Janitzki V. Minimally invasive PCNL (mini-perc). Alternative treatment modality or replacement of conventional PCNL?. Urologe A 2008;47:563–8.
5. Dindo D, Demartines N, Clavien PA. Classification of surgical complications:A new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann Surg 2004;240:205–13.
6. Singh Dongol UM, Bohora S. Outcome of percutaneous nephrolithotomy in the management of lower pole stones. J Nepal Health Res Counc 2018;16:274–8.
7. Preminger GM, Assimos DG, Lingeman JE, Nakada SY, Pearle MS, Wolf JS Jr, et al. Chapter 1:AUA guideline on management of staghorn calculi:Diagnosis and treatment recommendations. J Urol 2005;173:1991–2000.
8. Wickham JE, Kellett MJ. Percutaneous nephrolithotomy. Br J Urol 1981;53:297–9.
9. Alken P, Hutschenreiter G, Günther R, Marberger M. Percutaneous stone manipulation. J Urol 1981;125:463–6.
10. Segura JW, Patterson DE, LeRoy AJ, McGough PF, Barrett DM. Percutaneous removal of kidney stones. Preliminary report. Mayo Clin Proc 1982;57:615–9.
11. Clayman RV, Surya V, Miller RP, Castaneda-Zuniga WR, Amplatz K, Lange PH. Percutaneous nephrolithotomy. An approach to branched and staghorn renal calculi. JAMA 1983;250:73–5.
12. Liu C, Zhou H, Jia W, Hu H, Zhang H, Li L. The efficacy of percutaneous nephrolithotomy using pneumatic lithotripsy vs. the holmium laser:A randomized study. Indian J Surg 2017;79:294–8.
    13. Haghighi R, Zeraati H, Ghorban Zade M. Ultra-mini-percutaneous nephrolithotomy (PCNL) versus standard PCNL:A randomised clinical trial. Arab J Urol 2017;15:294–8.
    14. Borin JF. Prone retrograde laser lithotripsy facilitates endoscope-guided percutaneous renal access for staghorn calculi:Two scopes are better than one. J Endourol 2008;22:1881–3.
    15. Mishra DK, Agrawal MS. Use of a novel flexible mini-nephroscope in minimally invasive percutaneous nephrolithotomy. Urology 2017;103:59–62.
    16. Xu G, He Y, Zhao H, Jiang X, Feng G, Yang W, et al. Mini-nephroscope combined with pressure suction:An effective tool in MPCNL for intrarenal stones in patients with urinary tract infections. Urolithiasis 2016;44:445–50.
    17. Bozzini G, Aydogan TB, Müller A, Sighinolfi MC, Besana U, Calori A, et al. Acomparison among PCNL, miniperc and ultraminiperc for lower calyceal stones between 1 and 2 cm:A prospective, comparative, multicenter and randomised study. BMC Urol 2020;20:67.
    18. Malcolm JB, Derweesh IH, Brightbill EK, Mehrazin R, DiBlasio CJ, Wake RW. Tubeless percutaneous nephrolithotomy for complex renal stone disease:Single center experience. Can J Urol 2008;15:4072–6.
    19. Shah K, Agrawal MS, Mishra DK. Superperc:A new technique in minimally-invasive percutaneous nephrolithotomy. Indian J Urol 2017;33:48–52.
    20. Gupta S, Maurya AK, Pal DK. Observational prospective study for surgical outcome and anesthetic feasibility of tubeless and totally tubeless supine PCNL:A single centre initial experience. Turk J Urol 2019;45:146–9.
    21. Kara C, Resorlu B, Bayindir M, Unsal A. A randomized comparison of totally tubeless and standard percutaneous nephrolithotomy in elderly patients. Urology 2010;76:289–93.
    22. Grosso AA, Sessa F, Campi R, Viola L, Polverino P, Crisci A, et al. Intraoperative and postoperative surgical complications after ureteroscopy, retrograde intrarenal surgery, and percutaneous nephrolithotomy:A systematic review. Minerva Urol Nephrol 2021;73:309–32.
    23. Nikić P, Durutović O, Kajmaković B, Nale D, Bumbaširević U, Radovanović M, et al. Complications associated with percutaneous nephrolitholapaxy (PCNL)-our experience and literature review. Acta Chir Iugosl 2014;61:51–6.

    Mini Perc; Percutaneous Nephrolithotomy; Kidney stone; Minimally Invasive surgery

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