Minimally Invasive Tract in Percutaneous Nephrolithotomy for Renal Stones

Abstract

Aim:

The aim of this study was to assess the efficacy, safety, and morbidity of minimally invasive tract in percutaneous nephrolithotomy (Mini-PCNL) for renal stones in comparison with the standard PCNL.

Patients and Methods:

In a randomized trial, 69 patients (72 renal units) undergoing Mini-PCNL (group 1) from May 2004 to December 2007 were compared with a similar group of 111 (115 renal units) patients undergoing standard PCNL (group 2). Patients who needed more than one percutaneous tract or who had simultaneously undergone the two techniques on the same renal unit were excluded from the study group. Chi-square test was performed for statistical analysis of qualitative variables, and Student's t-test for quantitative variables. A p-value of <0.05 was considered significant.

Results:

The two groups had comparable demographic data and some outcome of characteristics such as time of stay in hospital, postoperative pain, dose of postoperative analgesics, ratio of positive fever, and stone-free rates for some types of stones (e.g., staghorn stone and simple renal pelvis stone). The stone-free rate for multiple caliceal stones (85.2% vs. 70.0% in group 1 and group 2) was significantly higher in the Mini-PCNL group (p < 0.05). The incidence of bleeding necessitating transfusion (1.4% vs. 10.4% in group 1 and group 2) was significantly lower in the Mini-PCNL group (p < 0.05). In group 1, operative time for different stone types such as staghorn stone, simple renal pelvis stone, and multiple caliceal stones were 134.3 ± 19.7, 89.4 ± 21.5, and 113.9 ± 20.3 minutes, respectively, which were significantly longer than that for group 2 (118.9 ± 21.5, 77.0 ± 17.6, and 101.2 ± 19.1 minutes) (p < 0.05).

Conclusion:

Mini-PCNL is safe and effective for managing renal calculi in adult patients. Although smaller working sheath is associated with longer operative time, Mini-PCNL has significantly lower incidence of bleeding necessitating transfusion and higher stone-free rate for multiple caliceal stones in comparison with the standard PCNL.

Introduction

T he advent and continuous evolution of percutaneous nephrolithotomy (PCNL) have led to a revolution in the management of renal stones.^1,2 PCNL is now the mainstay of treatment for patients with renal calculi and is a safe and successful method used for removal of different types of stones.³ Several modifications and refinements in nephroscopes have improved observation, and the use of slender nephroscopes has further enhanced the outcome and decreased the morbidity.⁴

In the present study, minimally invasive tract in PCNL (Mini-PCNL) is defined as a PCNL technique with small working sheath, which is performed using an 8/9.8F ureteroscope through a 16F percutaneous renal access tract. It seems that using a smaller-sized percutaneous tract than the standard PCNL has the potential advantage of decreased bleeding and trauma to renal parenchyma, which may effectively reduce intraoperative and postoperative complications.^5,6 However, no study is available to consider and compare the clinical curative effect of Mini-PCNL. We have performed a randomized comparison of Mini-PCNL with the standard PCNL to evaluate the efficacy, safety, and morbidity of Mini-PCNL for renal stones.

Patients and Methods

Between May 2004 and December 2007, 287 patients undergoing PCNL were incorporated into this randomized study at our center, including 142 in the Mini-PCNL group and 139 in the standard PCNL group. One hundred eighty patients (98 men and 82 women) who met the inclusion criteria were enrolled in this study. The inclusion criteria were single tract procedure and single technique on the same renal unit. The excluded patients included 49 patients (27 in the standard PCNL group and 22 in the Mini-PCNL group) who underwent secondary tract to assist clearing the caliceal stones, 52 patients in the Mini-PCNL group who were converted to the standard PCNL for low efficiency of fragmentation, and 6 patients who underwent open surgery to deal with the injury during the procedures. Of the 180 patients, 7 with bilateral stones underwent two PCNLs on separate occasions; a total of 187 PCNLs were conducted, which comprised 72 Mini-PCNLs and 115 standard PCNLs.

The preoperative work-up included blood analysis, urinalysis, urine culture and sensitivity, tests for renal function and metabolic disorders, ultrasonography, plain radiography of the kidneys, ureters, and bladder (KUB), and intravenous urography. All operations were done by three well-experienced urologists. The procedure was performed under general anesthesia. A 6F ureteral catheter was placed transurethrally, with the patient in the lithotomy position. A 16F Foley catheter was then placed and fixed to the ureteral access catheter with silk sutures. With the patient in a prone position, percutaneous access was created under fluoroscopic guidance after injection of contrast medium through the ureteral catheter. Once the correct position of the needle was confirmed, a 0.038-inch guidewire was inserted, and the tract was dilated over this guidewire by telescoping the metal dilators.

In the Mini-PCNL group, the tract was dilated up to 16F and a 16F peel-away sheath was secured in the tract. A Wolf 8/9.8F semirigid ureteroscope was used in the patients and the stone was fragmented by pneumatic lithotripsy (Swiss Pneumatic Lithoclast). The main fragments were manually evacuated using nephroscopic alligator forceps. A gentle wash with normal saline through the peel-away sheath assisted in removing small fragments. In the standard PCNL group, the tract was dilated up to 24F and a Wolf 20.8F nephroscope was used. The stone was fragmented by combining ultrasound (Swiss Lithoclast Ultra) and pneumatic lithotripsy (Swiss Pneumatic Lithoclast). The initial ultrasound fragmentation setting was 80%; this setting was increased if necessary during the procedures. Once complete clearance was confirmed fluoroscopically and endoscopically, a 5F Double-J stent was placed in an antegrade fashion and a nephrostomy tube was placed in all patients.

All patients had a complete blood count done on the first day after surgery to determine the decrease in hematocrit. All patients with supracostal access received intensive postoperative chest physiotherapy and spirometry and had a chest radiograph on the first day to detect any hydrothorax or pneumothorax. On the first and second days after surgery, patients were given a visual analog scale to analyze pain intensity, and pethidine was administered when they complained of severe pain. All patients were assessed by ultrasonography and KUB in the first postoperative week to confirm the stone clearance status and exclude the presence of urinoma. Stone-free status was defined as no stones visible on radiogram of KUB, and/or ultrasonogram on postoperative follow-up. Residual stones less than 4 mm were also considered to be stone free. Patients with residual stone were candidates for extracorporeal shockwave lithotripsy, or another PCNL. Both ultrasonography and radiography were repeated after 5 to 8 days, before the nephrostomy tube removal. The indwelling ureteral stent was kept for 3 to 5 weeks and removed cystoscopically under local anesthesia.

Statistical analysis was performed using the chi-square test for qualitative variables and the Student's t-test for quantitative variables. The level of significance was defined as p < 0.05.

Results

The two groups had comparable demographic data (Table 1). Postoperative data of the two groups are shown in Table 2. Mini-PCNL was associated with less hemoglobin decrease and bleeding necessitating transfusion (p < 0.05). Hospital stay days, postoperative pain, analgesia necessity, and postoperative fever rate were comparable between the groups (p > 0.05).

Table 1.

Demographic Data and Stone Characteristics of the Two Groups

Parameters	Mini-PCNL	Standard PCNL	p-Value
No. of renal units	72	115
Mean age (years)	37.2 (24–67)	39.6 (27–72)	>0.05
M/F ratio	1.2	1.2	>0.05
R/L ratio	1.5	1.4	>0.05
Stone type
Staghorn stones	18	29
Mean stone burden (cm²)	12.8	13.1	>0.05
Simple renal pelvis stones	27	46
Mean stone burden (cm²)	7.1	7.0	>0.05
Multiple caliceal stones	27	40
Number of stones	3.1 (2–7)	2.9 (2–6)	>0.05
Mean stone burden (cm²)	9.8	10.1	>0.05

Mini-PCNL = minimally invasive tract in percutaneous nephrolithotomy; M/F = male/female; R/L = right/left.

Table 2.

Summarized Postoperative Data of the Two Groups

	Mini-PCNL	Standard PCNL	p-Value
Hospital stay (days)	7.3 (6–12)	7.5 (6–15)	>0.05
Postoperative pain (VAS score)
Day 1	4.3 ± 2.1	4.3 ± 2.5	>0.05
Day 2	2.3 ± 1.7	2.5 ± 1.8	>0.05
Analgesic: pethidine (mg)	88.7 ± 40.6	94.3 ± 37.2	>0.05
Postoperative fever > 38.5°C, N (%)	15 (20.8%)	27 (23.5%)	>0.05
Decrease in hemoglobin level (g/dL)	0.53 ± 0.79	0.97 ± 1.42	<0.05
Bleeding necessitating transfusion, N (%)	1 (1.4%)	12 (10.4%)	<0.05
Pneumothorax	1 (1.4%)	0	>0.05
Urine leak > 12 hours	0	2 (1.7%)	>0.05
Stone type
Staghorn stones	18	29
Mean operative time (minutes)	134.3 ± 19.7	118.9 ± 21.5	<0.05
Stone-free rate, N (%)	13 (72.2%)	22 (75.9%)	>0.05
Simple renal pelvis stones	27	46
Mean operative time (minutes)	89.4 ± 21.5	77.0 ± 17.6	<0.05
Stone-free rate, N (%)	25 (92.6%)	42 (91.3%)	>0.05
Multiple caliceal stones	27	40
Mean operative time (minutes)	113.9 ± 20.3	101.2 ± 19.1	<0.05
Stone-free rate, N (%)	23 (85.2%)	28 (70.0%)	<0.05

N = number of patients; VAS = visual analog scale.

Bleeding necessitating transfusion was the only complication during the operation time, which occurred in one patient in the Mini-PCNL group and in seven patients in the standard PCNL group. Postoperative bleeding necessitating transfusion was recorded in five patients in the standard PCNL group. The total number of bleeding necessitating transfusion in the Mini-PCNL group was one (1.4%), which was significantly lower than that in the standard PCNL group (10.4%) (p < 0.05). Blood or packed cells depending on the hemoglobin level were transfused in these patients. Postoperative fever (temperature above 38.5°C) was detected in 15 (20.8%) patients in the Mini-PCNL group and 27 (23.5%) in the standard PCNL group (p > 0.05). All patients were treated with suitable antipyretic and antibiotics. There was no incidence of perirenal hematoma or urinoma. One patient from the Mini-PCNL group had postoperative pneumothorax and two patients from the standard PCNL group had urine leak for more than 12 hours. These patients recovered under close monitoring, without peculiar treatment.

Operative time was defined as the duration of the surgical procedure, beginning with percutaneous access. Operative time of the Mini-PCNL group for different stone types such as staghorn stone, simple renal pelvis stone, and multiple caliceal stones were 134.3 ± 19.7, 89.4 ± 21.5 and 113.9 ± 20.3 minutes, respectively, which were significantly longer than that for the standard PCNL group (118.9 ± 21.5, 77.0 ± 17.6, and 101.2 ± 19.1 minutes) (p < 0.05). With respect to stone-free rates, differences between the two groups in term of staghorn stone and simple renal pelvis stone were not statistically significant (p > 0.05). However, significant difference was present with respect to multiple caliceal stones, which was 85.2% (23/27) in the Mini-PCNL group and 70.0% (28/40) in the standard PCNL group.

Discussion

PCNL is the preferred treatment choice for staghorn stones, large renal stones, and multiple caliceal stones.⁷ The planning and execution of the initial access into the kidney is crucial to the outcome of PCNL. The access tract establishment is determined by the type of nephrolithotomy and is associated with the stone burden and location and distribution of the stone in relation to the collecting system. Watterson and colleagues⁸ have found that access-related complications were fewer and stone-free rates improved when the urologist made the percutaneous access. Generally, percutaneous access into the collecting system is safe when using a direct puncture through the overlying renal parenchyma into the fornix of the intended calix, to avoid injury to the interlobar vessels or segmental branches of the renal artery.⁹ However, the traditional PCNL usually needs the access tract dilated to 30F,¹⁰ which may increase risks of injury to major blood vessels and make it more difficult to recover from the puncture injury.

Mini-PCNL was introduced in the hope of decreasing the morbidity associated with larger nephroscopes and its access tract.^5,11,12 Jackman and colleagues⁵ used a 13F access sheath in preschool children to decrease the operative risk; they argued that a smaller tract leads to less tissue displacement and less nephron injury. Lahme and colleagues¹¹ reported in 2001 their experience of Mini-PCNL with a 12F rigid nephroscope and 15F Amplatz sheath to treat 1- to 2-cm renal calculi. In Zhaohui and associates' research,¹² they succeeded in dealing with upper urinary tract calculi in transplanted kidney by using an 8.5/11.5F nephroscope or an 8/9.8F ureteroscope through a 16F peel-away sheath. These studies revealed that, using a smaller-sized access tract than the standard PCNL, Mini-PCNL has the potential advantage of decreased risk of bleeding and tearing of the renal cortex but the disadvantage of need for longer time to dislodge stones than the standard PCNL makes it only selectively applied to special populations such as children and patients with renal insufficiency.

The present study was the first one that compared the clinical curative effects of Mini-PCNL and standard PCNL, correlating with different characteristics of kidney stones in adult patients. We found that some outcome characteristics such as time of stay in hospital, score of postoperative pain, dose of postoperative analgesics, ratio of positive fever, and stone-free rates for some types of stones (e.g., staghorn stones and simple renal pelvis stones) were not significantly different between the two techniques. Although the Mini-PCNL was beneficial to decrease the trauma to renal parenchyma, there was no advantage to shorten hospitalization time and reduce postoperative pain. However, the rate of bleeding necessitating transfusion in the Mini-PCNL group (1, 1.4%) was significantly lower than that of the standard PCNL group (12, 10.4%). Multiple factors contributed to postoperative fever in PCNL cases.¹³ Some authors report that the small tract in Mini-PCNL might result in a longer operation time and high pressure in the collecting system, which would cause pyelovenous or pyelosinus backflow, resulting in postoperative fever. However, recent studies have demonstrated that the renal pelvic pressure remained lower than the level of backflow during Mini-PCNL via 14F to 18F percutaneous tracts.¹⁴

In the present study, the mean operative time in the Mini-PCNL group was significantly longer than that in the standard PCNL group. In standard PCNL, stones were fragmented by combined usage of pneumatic and ultrasonic devices, whereas only pneumatic device is used in Mini-PCNL. Clinical evaluation has demonstrated that the combined usage of pneumatic and ultrasonic devices has significantly increased the efficiency of stone fragmentation.^15,16 Moreover, the larger access tract and the pumping function of the ultrasonic device improved stone retrieval time.

We compared the stone-free rate in different stone types between the two groups. The Mini-PCNL group has a higher stone-free rate for multiple caliceal stones than the standard PCNL, but the two groups have a comparable rate for staghorn stones and simple renal pelvis stones. It seems that both the techniques have similar good experience in dealing with simple renal pelvis stones and bad experience with staghorn stones. For multiple caliceal stones, the cause of significantly different stone-free rate may be associated with the endoscopes that were used in the two procedures. Because of the slender nature of the ureteroscope, entry into calix is easier and faster than using nephroscope, which could be effective in reducing the omission and dead ends during the operation.

Conclusion

Mini-PCNL is safe and effective for managing renal calculi in adult patients, especially in decreasing the rate of bleeding necessitating transfusion and improving stone-free rate for multiple caliceal stones. Although using a smaller working sheath extends the operative time, some outcome characteristics of Mini-PCNL, such as time of stay in hospital, dose of postoperative analgesics, ratio of positive fever, and stone-free rates for some types of stones (e.g., staghorn stone and simple renal pelvis stone), were not significantly different from that of standard PCNL.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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