Operating Times and Bleeding Complications in Percutaneous Nephrolithotomy: A Comparison of Tract Dilation Methods in 5537 Patients in the Clinical Research Office of the Endourological Society Percutaneous Nephrolithotomy Global Study

Abstract

Purpose:

The study investigated factors that affect operating times and bleeding complications associated with percutaneous nephrolithotomy (PCNL) in the PCNL Global Study.

Patients and Methods:

All patients who underwent PCNL for primary or secondary treatment of kidney stone indications during the study period (November 2007–December 2009) were eligible for inclusion. PCNL procedures were performed according to local clinical guidelines and practices. Nephrostomy tract dilation was performed using balloon dilation, metal telescopic dilation, or Amplatz serial dilation. Hematologic complications assessed included bleeding rates, transfusion rates, and preoperative and postoperative hematocrit values.

Results:

The median operating time with balloon dilation (n=2277) was significantly longer than with telescopic/serial dilation (n=3260) at 94.0 vs 60.0 minutes, respectively (P<0.0001). In the balloon dilation group, there was significantly more bleeding (9.4% vs 6.7%, respectively; P<0.0001) and more transfusions (7.0% vs 4.9%, respectively; P=0.001) compared with the telescopic/serial dilator group. Univariate analysis showed that the probability of bleeding complications was higher with balloon vs telescopic/serial dilation (odds ratio [OR] 1.75; P=0.0001) and larger sheath size (OR 1.42; P=0.0001). By multivariate analysis, sheath size but not dilation method was predictive of bleeding complications. Other significant predictive factors included operating time, stone load, and caseload.

Conclusion:

This study shows that in PCNL, factors that are associated with bleeding/transfusion include sheath size, operating time, stone load, and caseload.

Introduction

T he Clinical Research Office of the Endourological Society (CROES) was established in 2008 as a subgroup of the Endourological Society to provide a global collaborative framework to facilitate dialogue and to support research in endourology.^1,2 An area of special interest of CROES is percutaneous nephrolithotomy (PCNL) for the treatment of renal stones, and as such, centers that perform the procedure were invited to participate in the PCNL Global Study. The study was observational, and a database was established to collect data on consecutively treated patients for a period of 1 year. When the PCNL Global Study database closed in December 2009, it included information on more than 5800 patients from 96 centers in 26 countries.^3,4 The primary objective of the PCNL Global Study was to assess stone-free rates; numerous secondary analyses are ongoing or complete, including a comparison of methods used for nephrostomy tract dilation.

During PCNL, a large percutaneous tract into the kidney is established using pneumatic dilation (balloon dilation), rigid coaxial metal sheaths (passed over one another), or semirigid plastic sheaths (sequentially performed) that are inserted incrementally until the tract is dilated.^5

–8 More recently, a single-step technique involving the use of an Amplatz serial dilator over a metallic telescopic dilator (“one-shot”) has become accepted as a safe and effective technique.^9
–11 Balloon dilation is generally thought to be associated with shorter operating times and reduced radiation exposure than traditional multi-incremental methods, although balloon dilation is the more expensive option.^10,12,13

The initial PCNL Global Study analysis of nephrostomy tract dilation methods highlighted some important regional differences in the choice of dilator⁴; for example, balloon dilation was the method of choice in North America where cost was not an issue, whereas in South America and Asia, telescopic/serial tract dilation was preferred. In Europe, however, neither method predominated. Apart from cost, factors underlying the choice of dilator appeared to include obesity, previous kidney stone procedures, and high stone load, with balloon dilation favoring such patients.⁴

Complication rates in PCNL are reported from 29% to 83%,^14
–16 and in a recently completed PCNL Global Study analysis, the overall complication rate was 15%, which commonly involved bleeding.³ Balloon dilation appears to be preferred in patients who are deemed to be at an increased risk for complications,⁴ and balloon dilation is largely reported to have a better morbidity profile than metal telescopic dilation.^12,17,18 Nonetheless, clinical studies and retrospective reviews have also reported that balloon dilation has a similar morbidly profile as multi-incremental methods.^9,10,13

Contrary to previous reports, in the initial PCNL Global Study analysis of dilation methods, bleeding complications and transfusions were reported in 9.4% and 7.0% of patients, respectively, with balloon dilation, compared with 6.7% and 4.9% of patients, respectively, with telescopic/serial dilation.⁴ Therefore, in follow-up to the initial analysis of dilation methods, we conducted further analyses of the PCNL Global Study dataset to investigate operating times, hematologic safety, and risk factors for complications with balloon vs telescopic/serial dilators.

Patients and Methods

Data collection

This secondary analysis is part of a series from the CROES PCNL Global Study and was conducted to assess bleeding complications and operating times with balloon dilation compared with telescopic/serial dilation methods. The description of centers included in the study and data collection methods have been described previously.³ To reiterate, a steering committee of global experts in PCNL treatment was invited by the CROES council to direct the study. The target was to enroll 100 centers worldwide, including smaller centers, which performed <25 procedures a year, and “high volume” centers, which performed >100 procedures annually. Centers invited to participate were members of the Society of Endourology or were considered to have high expertise in the surgical field.

Electronic databases were made available to participating centers, and data were sent encrypted to the headquarters of CROES. Institutional Review Board approval was obtained at participating centers, if needed. The lead investigator at each center coordinated data collection and submitted regular updates to the central database. Each center provided data for consecutive PCNL patients for a study period of 1 year starting from the date of inclusion of the first patient. The first patient was entered into the database in November 2007, and the database was closed in December 2009.

Patients and procedures

There were no specific exclusion criteria, and all patients who underwent PCNL for the primary or secondary treatment of kidney stone indications during the study period were eligible for inclusion. PCNL procedures were performed according to local clinical guidelines and practices. A description of kidney stone indications and PCNL procedures is in the first PCNL Global Study analysis reported by de la Rosette and associates.³ Nephrostomy tract dilation was performed using balloon dilation, metal telescopic dilation, or Amplatz serial dilation and is described in a previous publication.⁴

Assessments

The variables included in the analysis were operating time, the incidence of bleeding, the number of transfusions, and preoperative and postoperative hemoglobin and hematocrit levels. Preoperative factors that were analyzed were body mass index (BMI), stone size, and the use of anticoagulation therapy. In patients receiving anticoagulation therapy, a subanalysis was performed. For each surgical procedure, operating time was recorded as the time from the first puncture to the completion of the stone removal. Outcomes were assessed according to Amplatz sheath size, defined as small (size 18F and below), medium (size 24F to 26F), large (sizes 27F, 28F, and 30F), and largest (sizes 32F, 33F, and 34F). The study centers were classified according to the volume of procedures performed in the study year; ie, caseload (low <25; medium 25–100; high >100), and according to the dilation method used (balloon only, telescopic/serial only; centers with 10% of patients dilated with either method were classed as “mixed”). To control for patient selection bias, outcomes were also assessed in a subgroup of patients who were at a low risk of bleeding. The low-risk subgroup included patients aged 30 to 60 years, with no history of anticoagulation therapy, and who had had lower-pole punctures.

Statistical analyses

Patients were grouped according to dilation method: Balloon dilation or telescopic/serial dilation. Continuous variables were analyzed using a Student t test (parametric) or a Mann-Whitney U test (nonparametric), and categorical variables were analyzed using the Pearson chi square test. Univariate and multivariate regression analyses for risk of bleeding/transfusion examined the following factors: Operating time, stone load, anticoagulant use, caseload, BMI, sheath size, and dilation method. Results of the univariate and multivariate logistic regression analyses were provided as OR, with 95% confidence intervals (CI). A P value of <0.05 was considered significant. The data were analyzed with SPSS version 16.0. The statistical analysis was supervised by a senior expert in the field.

Results

Patients

From a total of 5803 patients included in the Global PCNL database, 266 patients were excluded from the analysis because no information about the method of dilation was available. Of the 5537 patients included in the current analysis, 2277 (41.1%) were in the balloon dilation group and 3260 (58.9%) in the telescopic/serial dilation group. Patient characteristics of the two groups are as described previously.^3,4

Bleeding complications

Bleeding was reported in 9.4% of patients with balloon dilation compared with 6.7% with telescopic/serial dilation (P<0.0001; Table 1). Balloon dilation was also associated with significantly more transfusions (P=0.001) and greater drops in hematocrit level (P<0.0001) than telescopic/serial dilation, as well as significantly longer median operating times (P<0.0001; Table 1). A small proportion of the total cohort (313/5537; 5.7%) received perioperative anticoagulation therapy (including calcium carbasalate and warfarin), and in this subpopulation, bleeding and transfusion rates were similar in the balloon and telescopic/serial dilator groups (Table 2). In the 5224 patients who did not receive perioperative anticoagulation therapy, in the balloon dilator group, there was significantly more bleeding (9.2% vs 6.6%, P=0.001), and significantly more transfusions (6.9% vs 4.8%; P=0.002) than in the telescopic/serial dilator group (Table 2). There was a trend for slightly higher rates of bleeding, transfusions, and drops in hemoglobin level for patients who received anticoagulation therapy vs those who did not (Table 2).

Table 1.

Bleeding Complications and Operating Times

Characteristic	Balloon dilators n=2277	Telescopic/serial dilators n=3260	P value
Bleeding	9.4%	6.7%	<0.0001
Drop in hematocrit (mean/median)	4.48/4.50	2.48/2.40	<0.0001
Blood transfusion	7.0%	4.9%	0.001
Median operating time (min)	94.0	60.0	<0.0001

Table 2.

Bleeding Complications in Patients by Perioperative Anticoagulation Therapy Subgroup

	Received anticoagulation therapy n=313			No anticoagulation therapy n=5224
	Balloon	Telescopic/serial	P value	Balloon	Telescopic/serial	P value
Bleeding rate	10.9%	7.8%	0.476	9.2%	6.6%	0.001
Transfusion rate	8.3%	6.8%	0.721	6.9%	4.8%	0.002
Median Hb drop	4.8	3.0	0.03	4.50	2.40	<0.0001

Hb=hemoglobin.

Low-risk subgroup analysis

A total of 1890 patients were included in the low-risk subgroup. Bleeding was reported in 10% of patients with balloon dilation and 5.6% of patients with telescopic/serial dilation, and transfusion rates showed a similar trend (6.1% vs 3.0%). The median operating times were 90 and 60 minutes with balloon dilation and telescopic/serial dilation, respectively.

Center and sheath size

A total of 1274 patients were treated in balloon dilation only centers, 953 patients in telescopic/serial dilation only centers, and 1124 patients in centers classified as “mixed” (>10% of patients received either method). Those centers with <0% of either method were excluded from this specific analysis. Balloon dilator only centers had similar bleeding rates but higher transfusion rates and longer median operating times than telescopic/serial only centers (Table 3). Mixed centers had higher rates of bleeding and transfusions than centers using a single method (Table 3).

Table 3.

Bleeding Complications and Operating Times by Center Classified According to the Dilation Method

	Balloon dilation only centers n=1274	Mixed centers n=1124	Telescopic/serial dilation only centers n=953
Bleeding rate	9.1%	10.7%	9.6%
Transfusion rate	7.1%	8.3%	4.2%
Median operating time (min)	98	90	65

Mixed centers defined as those in which 10% of procedures performed by either method; n refers to the number of procedures performed.

In low-volume centers, median operating times with balloon vs telescopic/serial dilation were 105 minutes vs 108 minutes, respectively, and in medium-volume centers were 98 minutes vs 80 minutes, respectively (Table 4). The difference in mean operating time between procedures was much greater in high-volume centers compared with the differences reported in low- and medium-volume centers, at 90 minutes for balloon dilation vs 55 minutes for telescopic/serial dilation (Table 4). Another interesting trend was the risk of bleeding/transfusion with the balloon increased from low- to high-volume centers while the risk of bleeding/transfusion with telescopic dilators decreased from low- to high-volume centers.

Table 4.

Bleeding Complications and Median Operating Times by Study Center Volume

		Balloon dilation n=2277	Telescopic/serial dilation n=3260
Low volume	Bleeding rate	7.9%	12.9%
(<25 procedures/y)	Blood transfusion rate	4.8%	8.1%
	Operating time (min)	105	108
Medium volume	Bleeding rate	8.8%	11.6%
(25–100 procedures/y)	Blood transfusion rate	4.5%	4.5%
	Operating time (min)	98	80
High volume	Bleeding rate	10.4%	3.6%
(>100 procedures/y)	Blood transfusion rate	10.1%	4.8%
	Operating time (min)	90	55

Sheath size was associated with increased transfusion rates (chi square, 38.02; P<0.0001), with transfusion rates of 1.1% for the smallest sheath and 12.0% for the largest sheath (Table 5). A large sheath (27F, 28F, and 30F) was used in the majority of patients (3533/5214; 68%) and was associated with a transfusion rate of 5.9% (Table 5).

Table 5.

Transfusion Rate According to Amplatz Sheath Size

Sheath size	No. of patients	Blood transfusion (n [%])
Small (18F and below)	271	3 (1.1%)
Medium (24F and 26 F)	1039	50 (4.8%)
Large (27F, 28F, and 30F)	3533	208 (5.9%)
Largest (32F, 33F, and 34F)	371	45 (12.1%)

Blood transfusion status reported for 5214 patients.

Predictors of bleeding complications

Univariate logistic regression showed that balloon vs telescopic/serial dilation was associated with a higher rate of bleeding, with an OR of 1.75 (95% CI, 1.39–2.19; P=0.0001) (Table 6). Other factors that were predictive of bleeding complications were operating time, stone load, caseload, and sheath size (Table 6). BMI and anticoagulation therapy were not associated with an increased risk of bleeding complications. Multivariate logistic regression showed that the dilation method was not associated with increased bleeding rates (OR, 1.18; 95% CI, 0.91–1.52; P=0.2) (Table 7). The multivariate analysis showed that factors predictive of bleeding complications were operating time (P=0.0001), stone load (P=0.002), caseload (P=0.001), and sheath size (P=0.01) (Table 7). Because sheath size was a strong predictive factor, the relationship between method of dilation and sheath size was examined more closely. With the exception of the largest sheaths that were used in the balloon dilation group, bleeding and transfusions tended to increase with increasing size of sheath (Table 8). Use of medium and large sheaths was associated with higher rates of bleeding and transfusion with balloon dilation than with telescopic dilation.

Table 6.

Univariate Regression Analysis of Procedural and Patient Characteristics as Predictors of Bleeding or Transfusions

	Odds ratio for bleeding complications (95% confidence interval)	P value
Operating time (10 min interval)	1.107 (1.082–1.134)	0.0001
Stone load (50 mm² interval)	1.049 (1.035–1.068)	0.0001
Anticoagulation therapy	1.449 (0.865–2.427)	0.158
Caseload (center volume low-mid-high)	0.658 (0.567–0.764)	0.0001
BMI class^a	1.008 (0.893–1.138)	0.892
Sheath category (small, medium, large, largest)	1.427 (1.205–1.688)	0.0001
Dilation method (telescopic/serial=1.0)	1.751 (1.397–2.193)	0.0001

World Health Organization body mass index (BMI) class: Underweight (<18.49); normal (18.5–24.99); overweight (25.0–29.99); obese (≥30.0).

Table 7.

Multivariate Regression Analysis of Procedural and Patient Characteristics as Predictors of Bleeding or Transfusions

	Odds ratio for bleeding complications (95% confidence interval)	P value
Operating time (10 min interval)	1.066 (1.039–1.094)	0.0001
Stone load (50 mm² interval)	1.029 (1.011–1.048)	0.002
Anticoagulation therapy	1.261 (0.794–2.003)	0.327
Caseload (center volume low-mid-high)	0.721 (0.597–0.870)	0.001
Sheath category (small, medium, large, largest)	1.322 (1.068–1.637)	0.01
Dilation method (telescopic/serial=1.0)	1.182 (0.914–1.528)	0.201

Table 8.

Frequency of Bleeding and Blood Transfusion According to Method of Dilatation and Sheath Size

	Bleeding		Blood transfusion
Sheath size	Balloon n/N (%)	Telescopic/serial n/N (%)	Balloon n/N (%)	Telescopic/serial n/N (%)
Small (≤18F) N=271	0/37 (0%)	11/234 (4.7%)	0/37 (0%)	3/234 (1.3%)
Medium (24F, 26F) N=1039	9/107 (8.4%)	44/932 (4.7%)	6/107 (5.6%)	45/932 (4.8%)
Large (27F, 28F, 30F) N=3533	197/1978 (10.0%)	109/1555 (7.0%)	143/1978 (7.2%)	63/1555 (4.1%)
Largest (32–34F) N=371	2/95 (2.1%)	31/276 (11.2%)	6/95 (6.3%)	38/276 (13.8%)

Discussion

Percutaneous tract dilation is a major component of PCNL and is performed using a balloon dilator, metal telescopic dilator, Amplatz serial dilator, or an Amplatz dilator over a metallic telescopic dilator (one-shot). Each dilation method has pros and cons regarding operating times, patient selection, complications, and cost, and the method used is often determined by surgeon preference and local availability. In the present analysis of the PCNL Global Study, it was observed that median operating time was significantly shorter with telescopic/serial dilation at 60 minutes vs 94 minutes for balloon dilation. This was an unexpected finding, because previous studies suggest that operating time and fluoroscopic exposure is shorter with balloon vs telescopic dilation and similar for balloon vs serial dilation. Frattinni and associates¹⁰ conducted a clinical study of 78 consecutive patients and showed that mean (standard deviation [SD]) radiation exposure with telescopic, balloon, and one-shot dilation was 310 (216), 179 (90), and 262 (173) seconds, respectively. In a retrospective review of 143 patients reported by Davidoff and Bellman,¹⁷ surgery time was similar with the balloon vs Amplatz dilation at mean (SD) times of 108.8 (41.4) and 118.9 (46.6) minutes, respectively. Additional reports come from Safak and colleagues¹² who compared 95 balloon dilation procedures with a retrospective group of 30 consecutive Amplatz dilator procedures and reported mean (SD) operating times of 106.8 (41.4) vs 116.4 (23.7) minutes, respectively. In a review of 235 procedures, Gonen and coworkers¹⁹ reported that mean (SD) operating times were similar with Amplatz and balloon dilation at 86.3 (41.2) vs 85.7 (43.2) minutes, respectively.

In the PCNL Global Study, the trend for shorter operating times with telescopic/serial dilators was not seen in low-volume centers, where median operating times in the two groups were similar at 105 minutes with balloon and 108 minutes with telescopic/serial dilation. In high-volume centers, however, the trend was pronounced, and the median operating time for procedures using telescopic/serial dilation was 55 minutes compared with 90 minutes with balloon dilation. This suggests that in centers performing >100 procedures/year, surgeon experience can reduce the operating times with telescopic/serial methods to a greater degree than that achieved with balloon dilators.

Bleeding and blood transfusions are common complications of PCNL, and balloon dilation is generally considered to have a better hematologic morbidity profile than the other dilation methods. Indeed, because balloon dilation is radial, there is no risk of forward perforation, but with multi-incremental methods, there is a risk of perforation of any structure ahead or structures surrounding the tract. In the PCNL Global Study, however, bleeding was significantly higher with balloon at 9.4% compared with telescopic/serial dilation at 6.7%. A similar trend was seen for transfusions, which were significantly more common with balloon than telescopic/serial dilation at 7.0% and 4.9%, respectively. In the analysis including patients aged 30 to 60 years, with no anticoagulation therapy, and lower-pole punctures (ie, potential patient selection bias removed), balloon dilation was again associated with higher rates of bleeding and transfusions than telescopic/serial dilation.

Contrary to our results, previous studies have reported that each dilation method has a similar morbidity profile, or that balloon dilation is favorable compared with Amplatz serial dilation. In the clinical study by Frattinni and associates,¹⁰ telescopic, balloon, and one-shot dilation had similar hematologic safety profiles, and in the randomized study reported by Falahatkar and coworkers,⁹ telescopic and one-shot dilation had similar complication rates. In a review by Wezel and colleagues,¹³ although telescopic dilation was associated with significantly longer mean (SD) hospital stays than balloon dilation (7 [5] vs 5 [4] d, respectively), the methods had similar hematologic morbidity, and in the studies by Gonan and associates¹⁹ (Amplatz vs balloon dilation) and Amjadi and colleagues¹¹ (one-shot vs telescopic dilation), the methods had comparable complication profiles. Other studies, however, have reported that balloon dilation has a better safety profile than Amplatz dilation for transfusion rates (10 and 25 transfusions, respectively)¹⁷ and bleeding (13% and 16.6%, respectively).¹²

In the PCNL Global Study, center type by patient volume appeared to influence the rate of bleeding complications and transfusions, with higher rates in high- vs low-volume centers in the balloon dilator group. This may be because high-volume/more experienced centers have a higher proportion of difficult cases than less experienced, low-volume centers. The opposite is seen, however, with telescopic/serial dilation with lower transfusion rates in the high- vs low-volume centers. It is possible that procedures in “difficult to treat” patients, which may be more frequent in high-volume centers, are more likely to involve balloon than telescopic/serial dilation. This is supported by the previous PCNL Global Study analysis, which showed balloon dilation was more frequent than telescopic/serial dilation in patients with staghorn stones.⁴ Indeed, the multivariate analysis showed that caseload was predictive of bleeding and transfusions overall, again suggesting that higher volume centers may have a higher proportion of difficult to treat cases. Furthermore, in centers that used telescopic/serial dilation only, the transfusion rate was 4.2%, and in centers that used balloon dilation only, it was 7.1%, compared with 8.3% in centers using both methods. These findings for balloon vs telescopic/serial dilation by center volume may be associated with surgeon experience, meaning that bleeding complications are reduced with telescopic/serial dilation in high-volume centers or may again suggest that the use of balloon dilation is more common in high-risk patients.

Factors that were reported previously to be predictive of blood loss in PCNL include stone type, diabetes, and stone surface area.¹⁸ In the current univariate and multivariate analyses, operating time, stone load, caseload, and sheath size were significant predictors of bleeding and transfusions. In a previous PCNL Global Study analysis, BMI appeared to influence the choice of dilation method, with balloon dilation favored in obese patients. Indeed, it has been suggested that obesity increases the technical difficulty of PCNL, and this may increase the risk of complications, with some studies reporting a negative impact on complication rates^20

–23 and others reporting that BMI does not influence outcomes.^{15,21

–26} In the current univariate analysis, BMI and BMI by World Health Organization classifications were not associated with an increased risk of bleeding and transfusions.

Use of Amplatz serial dilation vs balloon dilation is reported to be a risk factor for bleeding complications.¹⁸ In the present study, univariate logistic regression showed that using balloon dilation significantly increased the risk of bleeding complication compared with telescopic/serial dilation with an OR of 1.75 (95% CI, 1.39–2.19), although dilation method was not shown to increase risk in the multivariate analysis. Further analysis revealed that smaller sheaths were used more frequently in the telescopic/serial dilator group. Moreover, in both the medium and large sheath groups, the rates of bleeding and blood transfusion were higher after balloon dilation than after telescopic/serial dilation. When more variables, such as operating time, caseload, history of anticoagulant use, or stone load, were included in the multivariate model, however, the method of dilation was not a significant predictor. It seems safe to conclude that because these factors may not be easily modifiable, the method of dilation and sheath size may be the only factors that provide the clinician with choice in the clinical approach to PCNL.

Although the results of the PCNL Study suggest that telescopic/serial dilation methods were less likely to cause bleeding than balloon dilation, this may be associated with factors that were unrelated to the procedure. For example, surgeons reporting the use of telescopic/serial dilators may have had longer experience, performed better punctures, or performed better overall, compared with those using balloon dilators. Further analyses are therefore ongoing to investigate these possibilities. Nonetheless, the results of this study offer an important insight into complications and dilation methods.

Conclusion

Telescopic/serial dilation and smaller sheath size are associated with shorter operating times than balloon dilation and larger sheath size. Factors predictive of bleeding complications include stone load, caseload, sheath size, and operating time. These analyses, however, do not take into account the experience of the surgeon, which will always influence outcomes.

Footnotes

Acknowledgment

The PCNL Global Study was supported by an unrestricted educational grant from Olympus. Prof. dr. A.H. Zwinderman is consulted to overlook the statistical aspects of the CROES studies.

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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