Predictors of Fluoroscopy Time during Percutaneous Nephrolithotomy: Impact of

Postgraduate Urology Trainees and S.T.O.N.E. Nephrolithometry Score

Yasser A. Noureldin1,2

Mohamed A. Elkoushy,1,3

Sero Andonian1

1Division of Urology, McGill University Health Centre, Montreal, Québec, Canada

2Department of Urology, Benha University Hospital, Benha University, Benha, Egypt

3Department of Urology, Suez Canal University, Ismailia, Egypt

Corresponding Author:

Sero Andonian, MD, MSc, FRCS(C), FACS

Assistant Professor of Urology,

McGill University Health Centre

687 Pine Ave. West, Suite S6.92

Montreal, Québec, Canada H3A 1A1

Tel: 514-843-2865; Fax: 514-843-1552

E-mail: sero.andonian@muhc.mcgill.ca

Word count:

Abstract: 276

Manuscript: 2323

Key words: Percutaneous nephrolithotomy, Fluoroscopy, Ionizing Radiation, and

Scoring Method.

Acknowledgements: This work was supported by grants from Fonds de la Recherche en

Santé du Québec (FRSQ) to Dr Sero Andonian.

Conflict of Interest: None.

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ABSTRACT

Objectives: To determine predictors of Fluoroscopy Time (FT) during Percutaneous

Nephrolithotomy (PCNL) and assess the impact of urology Post-Graduate Trainees

(PGTs) and S.T.O.N.E. Nephrolithometry Score.

Methods: A prospective review of patients undergoing PCNL between 2010 and 2013 at

a tertiary health care centre was performed. Patients’ demographics, stone characteristics,

including S.T.O.N.E. Nephrolithometry Score, and operative data were compared among

PGTs. Predictors of FT were determined using univariate and multivariate models.

Results: A total of 103 PCNLs were assisted by 10 PGTs from Post-Graduate Years

(PGY) 4 and 5 [37 (35.9%) and 66 (64.1%) cases, respectively)]. Sixty percent of patients

were males with a mean age of 55.2±1.5 years and a mean BMI of 26.4±0.5 kg/m2. The

mean S.T.O.N.E score was 7.7±0.1, with tubeless PCNL in 53 (51.5%) cases. The mean

FT was 120±5 seconds, mean operative time was 102±3.5 minutes and mean length of

hospital stay was 4.2±0.34 days. The overall stone-free rate was 72.8%. PGY-5 trainees

used significantly less FT than PGY-4 trainees (115±6 vs. 130±7 sec; p=0.04). FT

significantly correlated with the number of involved calyces (r= 0.24, p= 0.02), number

of punctures (r=0.6, p=0.01), number of tracts (r=0.4; p=0.01), and operative time (r=0.4,

p=0.01). In addition, cases with estimated blood loss (EBL) <250 mL were associated

with significantly less FT than those with blood loss >250 mL (109±5.1 vs. 148.2±10.9

sec; p=0.001). On multivariate analysis, the number of punctures, EBL and operative

time were found to be independent predictors for FT. However, there was no correlation

of FT with S.T.O.N.E. Nephrolithometry Score (r=0.16; p=0.1).

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Conclusions: The number of punctures, EBL and operative time were the only

independent predictors of prolonged FT during PCNL.

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INTRUDUCTION

Since Percutaneous Nephrolithotomy (PCNL) was introduced in 1976 1, it has

become a widely-accepted option for management of large renal stones due to its high

success rate, low morbidity and early convalescence.2,3

However, it is associated with the

highest radiation exposure among the different endourological procedures.4 Therefore, it

is important to identify factors associated with increased Fluoroscopy Time (FT) and

Effective Radiation Dose (ERD) during PCNL. There are only two previous studies

examining this relationship. While Tepeler et al found that FT was significantly

prolonged in patients with increased stone burden and multiple access tracts, Mancini et

al found that increased Body Mass Index (BMI), stone burden, and multiple access tracts

were associated with increased ERD.5,6

The S.T.O.N.E. Nephrolithometry Score has been

recently described as an objective assessment tool for pre-operative evaluation of

complexity of PCNL. However, previous studies did not examine the impact of

S.T.O.N.E. Nephrolithometry Score on FT.

Recently, significant variations have been shown among different surgeons and

Post-Graduate Trainees (PGTs) in FT during retrograde ureteroscopy.7,8

Yet, the impact

of PGTs on FT has not been evaluated during PCNL. Therefore, the aim of the present

study was to determine predictors of FT during PCNL and assess the impact of urology

PGTs and S.T.O.N.E. Nephrolithometry Score.

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MATERIALS AND METHODS

Study design and Enrollment:

Approvals from Institutional Research Ethics Board (No. 14-050-GEN) and

Director of Professional Services of McGill University Health Centre were obtained.

Chart and electronic data were reviewed for all patients undergoing PCNL between 2010

and 2013. All PCNLs were performed by a single fellowship-trained endourologist (SA)

with the assistance of PGTs from Post-Graduate Years (PGY) 4 and 5. There are no

endourology clinical fellows at this centre. Therefore, PCNLs are considered to be

cases appropriate for PGY-5 trainees. When PGY-5 trainees were not available,

PGY-4 trainees performed these cases. Therefore, the PGY level was not chosen

according to the difficulty of PCNL cases. PGTs attempted the first puncture

regardless of their level of training and previous PCNL experience. In addition, the

person who was performing the procedure or puncture, whether it is the attending

urologist or the PGT, controlled the foot switch for fluoroscopy. Patients who

underwent second-look PCNL, or PCNL without involvement of any PGT were

excluded. In addition, patients who had their percutaneous access obtained by the

interventional radiologist were also excluded from the study. All PGTs received annual

lectures on Radiation Safety and were instructed to minimize FT intra-operatively.

Procedure:

The attending endourologist was scrubbed throughout every PCNL case. All

patients received broad-spectrum antibiotics peri-operatively. Under the benefit of

general anesthesia, patients underwent flexible cystoscopy to place a 5F ureteral catheter

and secure it to an indwelling 18F Foley urethral catheter. All patients underwent PCNL

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procedure in the prone position as previously described.9 At the end of the procedure,

patients had antegrade indwelling double-pigtail 6F ureteral stents inserted. For tubeless

cases, the skin was closed with 4-0 absorbable suture and for standard PCNL cases a 20F

council-tip nephrostomy was inserted. The FT was calculated from the beginning to the

end of the procedure including flexible cystoscopy and insertion of the ureteral catheter.

The operative time included both cystoscopy and PCNL procedure. A puncture was

defined as a needle pass through the kidney without necessarily tract dilation. A

tract is when a puncture was dilated.

Outcome measures:

Patient and PGT characteristics were collected prospectively on data sheets that

were filled out by the attending surgeon immediately post-operatively. Variations in FT

were assessed among PGTs, PGY level, presence and degree of hydronephrosis (mild,

moderate, and severe), presence of pre-operative indwelling ureteral stents, presence of

post-operative nephrostomy tube, Estimated Blood Loss (EBL), and site of tract (upper,

mid and lower poles) were compared. In addition, correlation of FT with stone volume

(mm2), Hounsfield Units (HU), number of punctures, number of tracts, tract length,

number of involved calyces and operative time were assessed. Moreover, the impact of

PCNL complexity on FT was determined by comparing the S.T.O.N.E. Nephrolithometry

Score with FT.

S.T.O.N.E. Nephrolithometry Score:

This score is calculated by adding five parameters obtained from the pre-operative

non-contrast computed tomography (NCCT) of the kidney stone. These parameters

include the Stone size (mm2) (1-399=1, 400-799=2, 800-1599=3, and ≥1600=4), Tract

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length (mm) (≤100=1, >100=2), Obstruction or hydronephrosis (no or mild=1, and

moderate or severe=2), Number of involved calyces (pelvis involvement, one or two

calyces=1, three calyces=2, and staghorn stone=3), and stone Essence or density (HU)

(≤950=1, and >950=2). The total S.T.O.N.E. Nephrolithometry Score ranges from 5-13,

with the score of 5 representing the simplest PCNL and the score of 13 representing the

most complex PCNL.10

All procedures were performed using the OEC 9900 Elite (General Electric) C-

arm unit. FT was obtained from the timer on the C-arm unit and recorded by the

attending urologist on the data sheets. These FTs were confirmed from the radiology

reports. PGTs assisting in the PCNL procedures controlled the foot pedal. Prior to

November 2010, all PCNL cases were performed using Standard Fluoroscopy (SF) with

refresh rates of 30 frames per second. After November 2010, Pulsed Fluoroscopy (PF) at

a refresh rate of 4 frames per second was routinely used. We have previously shown that

Pulsed Fluoroscopy (4 frames per second) resulted in 65% less Fluoroscopy Time than

when Standard Fluoroscopy (30 frames per second) was used during PCNL.11

Therefore,

in order to standardize the FT used in the present study, the Fluoroscopy Times obtained

using SF prior to November 2010 were multiplied by 0.35. 11

Data analysis:

Comparative and descriptive data were presented in terms of numbers,

percentages, means and standard errors of mean. Links between continuous variables

were assessed using the Spearman rank correlation coefficient or the Pearson's

correlation coefficient, whenever appropriate. Categorical variables were compared

using Fisher’s exact test while continuous variables were compared using the Mann-

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Whitney U-test and Kruskal-Wallis test or independent sample (t) test and one way

ANOVA test, whenever appropriate. Two tailed p-value <0.05 was considered

statistically significant. Univariate and multivariate linear regression analyses were

performed to determine the independent predictors of FT. Statistical analysis was

performed using the Statistical Package of Social Sciences for Windows (SPSS, Chicago,

IL) version 20.

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RESULTS

Out of 130 PCNL cases, 103 were included in the data analysis. Twenty-seven

cases were excluded; 15 had the access tract performed by interventional radiology, 6 had

second-look PCNLs, and 6 were performed without the assistance of any PGTs. These

103 PCNL cases were assisted by 10 PGTs (coded A to J) from PGY-4 and PGY-5,

including 37 (35.9%) PCNLs assisted by PGY-4 trainees and 66 (64.1%) PCNLs assisted

by PGY-5 trainees. [The median number of cases assisted per PGT was 9 (7-17)]. The

overall stone-free rate was 72.8% after the primary PCNL procedure. Other pre-operative

and demographic data are presented in Table 1.

The mean FT (sec) utilized by each PGT from A to J was (106±12.8, 101.3±15,

136±15.6, 136.6±10.5, 130.6±32, 108±8.3, 112.3±8.8, 103.8±15.5, 131.3±19.3, and

128.4±23 sec; p=0.45), respectively. PGY level significantly affected FT, where PGY-5

trainees utilized significantly less FT than PGY-4 trainees (115±6 vs. 130±7 sec; p=0.04)

(Table 2; Figure 1). In addition, there was no significant difference in the mean FT

between PGTs who performed > 9 PCNLs compared to PGTs with ≤ 9 PCNLs

(116±12 vs 119±5, p=0.6). Similarly, there were no significant differences in FT

among PCNL cases performed in 2010, 2011, 2012, and 2013 years with mean FT of

117.7±10.7, 127.7±9, 104.4±6.9, and 128.3±12.5 seconds, respectively (p=0.3).

However, there was a significant correlation between FT and number of involved calyces

(r= 0.24, p= 0.02), number of punctures (r=0.6, p=0.01), number of tracts (r=0.4; p=0.01),

and operative time (r=0.4, p=0.01). Furthermore, PCNLs where the EBL was <250 mL

were associated with significantly lower FT than those with EBL ≥250mL (109±5.1 vs.

148.2±10.9 sec; p=0.001). There was significant correlation between the number of

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punctures and number of involved calyces (r=0.3; p=0.001), and operative time

(r=0.4; p<0.001). In addition, there was significant correlation between operative

time and S.T.O.N.E. score (r=0.4; p<0.001).

There was no correlation between FT and S.T.O.N.E. Nephrolithometry Score

(r=0.16; p=0.1), stone volume (r=0.07; p=0.5), stone HU (r=0.05; p=0.6), tract length

(r=0.04; p=0.7) and BMI (r=0.001; p=0.1) (Figure 2). There was no association

between FT and stone-free status. The mean FT in stone-free cases was 117±6.2 (sec)

compared with 130±7.9 (sec) in non stone-free cases (p=0.2). Similarly, FT was not

affected by the presence of pre-operative indwelling ureteral stents (p=0.4), presence of

hydronephrosis (p= 0.3), degree of hydronephrosis (p=0.5), involvement of renal pelvis

(p=0.2), (tract site [upper, middle or lower calyx] (p=0.1) or insertion of post-operative

nephrostomy tube (p=0.2).

On univariate linear regression analysis, significantly longer FT was associated

with PGY-4 trainees, increased number of involved calyces, increased number of

punctures, increased number of tracts, combined upper and lower tracts, operative time

and EBL ≥ 250 mL (Table 3). However, on multivariate linear regression analysis, only

the number of punctures, operative time, and EBL ≥ 250 mL maintained their

significance as independent predictors of FT during PCNL (Table 4).

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DISCUSSION

Surgeon behavior is one of the important modifiable predictors of FT during

endourological procedures. Previous studies have shown that there were significant

differences in FT among surgeons and PGTs assisting in ureteroscopies.8 Therefore, the

hypothesis for the present study was that there would be significant differences in FT

among PGTs assisting PCNL. Although PGY-5 trainees used significantly less FT than

PGY-4 trainees (115±6 vs. 130±7 sec; p=0.04) (Figure 1), there were no significant

differences among PGTs assisting PCNLs (p=0.45). There could be several theories to

explain the lack of significant differences among PGTs. First, the mean FT in the present

study is 120±5 seconds (2 minutes), which is much shorter than previous modern series

examining FT during PCNL. For example, the study of Tepeler et al had a mean FT of

10.19±6.3 minutes.5

Another study by Mancini et al found mean FT of 7.76±0.9 minutes.6

Therefore, the amount of FT used in the present study was already low with minimal

variations among the different PGTs (Figure 1). Second, all PGTs attended radiation

safety lectures and were advised to minimize intra-operative fluoroscopy as much as

possible. Third, PF at 4 frames per second was used in all cases since November 2010.

PF has been recently shown to decrease FT by 65%.11

Fourth, the median number of

PCNLs assisted by each trainee was only 9, which may not have been enough since 36 to

45 PCNLs are required to achieve competency.12,13

In addition, the median number of

months that PGTs rotated through the endourology site was 3.5 months. Fifth, the

present study was performed prior to acquisition of virtual reality simulator to train

percutaneous renal access. Nonetheless, PGY-5 trainees used significantly less FT than

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fin

al p

ublis

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may

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from

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pro

of.

11

11

PGY-4 trainees, indicating that the more experienced senior trainees used significantly

less FT during PCNL.

The S.T.O.N.E. Nephrolithometry Score System has been recently devised for

objective assessment PCNL complexity, 10

and it has been shown to correlate with stone-

free status. 10,14

Although FT significantly correlated with the number of involved calyces

(r= 0.24, p= 0.02), there was no correlation between FT and the S.T.O.N.E.

Nephrolithometry Score. Perhaps the lack of correlation has to do the way S.T.O.N.E.

Nephrolithometry Score is calculated. The higher the number of involved calyces, the

higher the N number and thus the higher the S.T.O.N.E. Nephrolithometry Score.

However, it has been previously shown that non-branched stones (lower number of

involved calyces) are associated with significantly higher Effective Radiation Dose when

compared with branched stones (higher number of calyces).6 Therefore, the current

findings of lack of relationship between S.T.O.N.E. Nephrolithometry Score and FT are

congruent with previous published results.

Previous studies have shown that multiple access tracts and large stone burden

were associated with prolonged FT. 5,6

This was not consistent with the current study

where the increase in number of tracts and stone volume were not significantly associated

with prolonged FT on multivariate analysis. This could be due to the relatively short FT

(2 minutes) used in the present study due to several factors including the use of Pulsed

Fluoroscopy at 4 frames per second. Nevertheless, the number of punctures significantly

correlated with FT. This may be explained by the fact that fluoroscopy is mainly used

during percutaneous access rather than tract maturation and stone extraction. Whereas the

number of punctures was not assessed in previous studies, the advantage of the present

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fin

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may

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12

12

study is that the number of punctures was recorded prospectively after each procedure.

Patient age, sex, and BMI did not significantly affect the FT, which is consistent with

what has been previously reported. 5,6

In addition, the present study revealed no effect of

stone HU, presence or degree of hydronephrosis, pre-operative indwelling ureteral stent,

tract length, post-operative nephrostomy tube insertion on FT. This is similar to the

previously published study. 5

This study is not without limitations including its retrospective nature, despite the

fact that most of the data were prospectively collected by the attending surgeon

immediately post-operatively on PCNL data sheets. Another limitation is that the

intra-operative blood loss was estimated rather than reporting hemoglobin drop. In

addition, the relatively small number of cases (median of 9 PCNLs) assisted by each PGT

is another limitation since it is estimated that up to 45 PCNLs are required to achieve

competency.12,13

This precluded calculation of the learning curve for PGTs. Another

limitation is the lack of data regarding the different level of involvement of the

attending urologist in each case. Finally, the dose area product was not available to

calculate the effective radiation dose (ERD). Therefore, FT was used as a surrogate for

ERD. Nevertheless, this the first study to report on the effect of S.T.O.N.E.

Nephrolithometry Score and PGTs assisting in PCNLs on FT. In addition, this is the first

study to report the number of punctures as an independent predictor of prolonged FT

during PCNL.

Conclusions

The number of punctures, EBL and operative time were the only

independent predictors of prolonged FT during PCNL.

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13

13

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14

14

REFERENCES

1. Fernstrom I, Johansson B. Percutaneous pyelolithotomy. A new extraction technique.

Scand J Urol Nephrol. 1976; 10(3): 257-259.

2. Preminger GM, Clayman RV, Hardeman SW, et al. Percutaneous nephrostolithotomy

vs. open surgery for renal calculi: A comparative study. JAMA 1985; 254(8):1054–

1058.

3. Brannen GE, Bush WH, Correa RJ, et al. Kidney stone removal: Percutaneous versus

surgical lithotomy. J Urol 1985; 133(1):6–12.

4. Hellawell GO, Mutch SJ, Thevendran G, et al. Radiation exposure and the urologist:

What are the risks? J Urol. 2005; 174(3):948–952.

5. Tepeler A, Binbay M, Yuruk E et al: Factors affecting the fluoroscopic screening

time during percutaneous nephrolithotomy. J Endourol 2009; 23(11): 1825-1829.

6. Mancini JG, Raymundo EM, Lipkin M et al: Factors affecting patient radiation

exposure during percutaneous nephrolithotomy. J Urol 2010; 184(6): 2373.

7. Ngo TC, Macleod LC, Rosenstein DI, et al. Tracking intraoperative fluoroscopy

utilization reduces radiation exposure during ureteroscopy. J Endourol 2011;25:763-

767.

8. Elkoushy MA, Andonian S. Variations among urology trainees in their use of

fluoroscopy during ureteroscopy. J Endourol 2013; 27(1):19-23.

9. Shahrour W, Andonian S. Ambulatory Percutaneous Nephrolithotomy: Initial Series

Urology 2010; 76: 1288–1292.

10. Okhunov Z, Friedlander JI, George AK, et al. S.T.O.N.E. Nephrolithometry: Novel

surgical classification system for kidney calculi. Urology 2013a. 81(6): 1154-1160.

11. Elkoushy MA, Shahrour W, Andonian S. Pulsed fluoroscopy in ureteroscopy and

percutaneous nephrolithotomy Urology 2012; 79 (6): 1230–1235.

12. Ziaee SAM, Sichani MM, Kashi AH, et al. Evaluation of the Learning Curve for

Percutaneous Nephrolithotomy Urol J 2010; 7(4): 226-231.

13. Jang WS, Choi KH, Yang SC, et al. The learning curve for flank percutaneous

nephrolithotomy for kidney calculi: a single surgeon’s experience. Korean J Urol

2011; 52(4):284-288.

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s N

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otom

y: I

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stgr

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rolo

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rain

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S.T

.O.N

.E. N

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(do

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The

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of.

15

15

14. Okhunov Z, Helmy M, Perez-Lansac A, et al. Interobserver reliability and

reproducibility of S.T.O.N.E. Nephrolithometry for renal calculi. J Endourol 2013b;

27(10):1303-1306.

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16

16

Figure Legends

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17

17

Figure 1: Variations among PGTs in their use of Fluoroscopy Time during PCNLs

stratified by the number of PCNLs performed at each PGY level.

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18

Figure 2: Effect of PCNL complexity on Fluoroscopy Time

ABBREVIATIONS

BMI: Body Mass Index

EBL: Estimated Blood Loss

ERD: Effective Radiation Dose

FT: Fluoroscopy Time

HU: Hounsfield Units

LOS: Length of hospital stay

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N/A: Not Applicable

PCA: Percutaneous access

PCNL: Percutaneous Nephrolithotomy

PCS: Pelvi-Calyceal System

PGTs: Post-Graduate Trainees

PGY: Post-Graduate Year

PF: Pulsed Fluoroscopy

SF: Standard Fluoroscopy

TABLES

Table 1: Demographic and peri-operative parameters

Parameter Mean± SE Range

Patient age (years) 55.2 ± 1.5 17 - 85

Gender (Male/Female) (n, %) 60 (58.3%) / 43 (41.7%) N/A

BMI (kg/m2) 26.4 ± 0.5 17 - 46

S.T.O.N.E. Nephrolithometry Score 7.7 ± 0.1 5 - 12

Stone size (mm2) 621.7 ± 57.6 250 - 2700

Stone HU 902 ± 32 316 - 1766

Left-sided stone 61 (59.2%) N/A

Pelvis involvement 73 (70.9%) N/A

Pre-operative indwelling ureteral stent 57 (55.3%) N/A

Number of punctures 2.1 ± 0.1 1-6

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Number of tracts 1.2 ± 0.04 1-3

Tract length (mm) 96.9 ± 2.3 59 - 170

Post-operative NT 53 (51.5%) N/A

Fluoroscopy Time (sec) 120 ± 5 45 - 330

Operative time (min) 102 ± 3.5 60 - 240

Length of hospital stay (days) 4.2 ± 0.34 1-18

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Table 2: Baseline patient and stone characteristics stratified by PGY level

Variables PGY-4

(n = 37 cases)

PGY-5

(n = 66 cases)

p-value

Age (years) 53.9±2.8 55.9±1.8 0.6

Male gender 23 (62.2%) 37 (56.1%) 0.7

BMI (kg/m2) 26.3±1 26.5±0.6 0.8

Hydronephrosis 13(35.1%) 25(37.9%) 0.8

Left-side stone 21(56.8%) 40(60.6%) 0.8

S.T.O.N.E. Nephrolithometry Score 7.7±03 7.7±0.2 0.9

Stone volume (mm2) 632.6±92 615.5±73 0.8

Hounsfield unit (HU) 839±51 936±40 0.2

Number of calyces involved 1.48±15 1.45±11 0.9

Pelvis involvement 27(73%) 46(69.7%) 0.8

Pre-operative ureteral stent 25(67.6%) 32(48.5%) 0.06

Number of punctures 2.16±17 2.04±13 0.4

Number of tracts 1.3±0.08 1.2±0.04 0.2

Tract length (mm) 93.5±4.3 98.6±2.7 0.1

Operative Time (min) 101±6 102±4 0.9

Fluoroscopy Time (sec) 130±7 115±6 0.04

EBL <250 mL 24(64.9%) 50(75.8%) 0.3

Post-operative nephrostomy tube 14(37.8%) 36(54.5%) 0.1

LOS (days) 3.7±0.6 4.5±0.4 0.05

Stone-free 29(78.4%) 46(69.7%) 0.4

* Data were presented as mean±standard error of mean or number (n) and percent (%),

whenever appropriate.

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Table 3: Impact of patient and operative parameters on Fluoroscopy Time

Variable Univariate Linear Regression analysis

Change/sec p-value

Patient age (10 years) 9 0.78

Male gender 0.9 0.93

BMI 0.3 0.76

PGY- 4 Trainees 14.1 0.04

PGT

A -0.2 0.16

B -0.2 0.07

C -0.01 0.97

D Reference Reference

E -0.03 0.12

F -0.2 0.28

G -0.13 0.15

H -0.17 0.82

I -0.03 0.70

J -0.05 0.78

Left-sided stone 15 0.13

Stone size (100 mm2) 13 0.14

Radiolucent stone 18 0.26

S.T.O.N.E. Nephrolithometry Score 5 0.1

Number of calyces involved 13 0.02

Pelvis involvement -12 0.29

Presence of hydronephrosis -6 0.58

Pre-op indwelling ureteral stent 7 0.46

Number of punctures 27 <0.001

Number of tracts 43 <0.001

Site of

the

tract

Upper calyx 10 0.46

Middle calyx 6 0.63

Lower calyx Reference Reference

Combined Upper & middle 41.5 0.40

Combined Upper & lower 67.5 0.002

Combined Middle & lower 6 0.77

Tract length .07 0.77

Post-operative Nephrostomy Tube 13 0.19

Operative time (10 min) 6 <0.001

EBL ≥ 250 mL 39 <0.001

Stone-free status -13 0.25

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Table 4: Predictors of Fluoroscopy Time on multivariate regression analysis

Variable Multivariate Linear Regression analysis

Change/sec p-value

PGY-4 10.6 0.07

Number of involved calyces 0.88 0.86

Number of punctures 20.5 < 0.001

Number of Tracts 2.49 .83

Combined upper and lower calyceal

tracts 11.93 0.05

Operative time (min) 0.31 0.02

Blood loss ≥ 250 cc 23.6 0.01

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