Urolithiasis (2014) 42:87–93 DOI 10.1007/s00240-013-0614-3
ORIGINAL PAPER
Is the supine position superior to the prone position for percutaneous nephrolithotomy (PCNL)? Xiaohua Zhang • Leilei Xia • Tianyuan Xu • Xianjin Wang • Shan Zhong • Zhoujun Shen
Received: 25 July 2013 / Accepted: 12 October 2013 / Published online: 20 October 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract The objective of this study is to update the two previous meta-analyses in order to evaluate the efficacy and safety of percutaneous nephrolithotomy (PCNL) for patients in the prone position versus supine position. An electronic database search of MEDLINE, EMBASE, google scholar, and the Cochrane library was performed up to June, 2013. All studies comparing prone with supine position for PCNL were included. The outcome measures were stone-free rate, operative time, complication and hospital stay. Two randomized controlled trials (RCTs) and 7 non-RCTs, including 6,413 patients (4,956 patients in the prone position group and 1,457 patients in the supine position group), met the inclusion criteria. Meta-analysis of extractable data showed that PCNL in the supine position was associated with a significantly shorter operative time (WMD: 21.7; 95 % CI 2.46–40.94; p = 0.03) but lower stone-free rate (OR: 1.36; 95 % CI 1.19–1.56; p \ 0.0001) than PCNL in the prone position. There was no difference between the two positions regarding hospital stay (WMD = 0.05; 95 % CI -0.16–0.25; p = 0.66) and complication rate (OR: 1.1; 95 % CI 0.94–1.28; p = 0.24). In conclusion, the present study found different results from the two previous meta-analyses results regarding stone-free rate; PCNL in the supine position had a significantly lower stone-free rate than that in prone position. Keywords Percutaneous nephrolithotomy PCNL Prone Supine X. Zhang and L. Xia contributed equally to this work. X. Zhang L. Xia T. Xu X. Wang S. Zhong Z. Shen (&) Department of Urology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, 197 Ruijin No. 2 Road, Shanghai 200025, China e-mail: [email protected]
Introduction Since the first successful stone extraction through a nephrostomy in 1976 [1], percutaneous nephrolithotomy (PCNL) has became the preferred procedure for the treatment of renal stones, especially for large, complex and staghorn calculi. For decades, this technique has been performed in the prone position. More recently, particular interest has been focused on supine position because as compared to the prone position, the supine position has the following advantages [2]: safer and easier for the patient; less cardiovascular change; no need for patient repositioning (with less operative time and less relevant risk of nervous system injuries); and more comfortable and less radiation exposure to the surgeon; but also allows a simultaneous PCNL and ureteroscopy. Despite the potential advantages, the supine position necessitates more lateral displacement of the renal puncture site than the prone position, which may increase the possibility of visceral injuries and cause trauma to intrarenal vessels [3]. Therefore, controversy has emerged as to which is the better position for PCNL. Two very recent meta-analyses comparing supine versus prone position for PCNL have been published [4, 5], both of which were based on 4 publications that met their inclusion criteria—2 prospective RCTs and 2 case control studies. Both meta-analyses concluded that the two positions showed equivalency for stone-free rate, length of hospital stay, and complication rate. In addition, both found supine PCNL had shorter operative time than prone PCNL. Despite these two meta-analyses published, many studies have been published in the literature from then and yielded inconsistent results. The best access to PCNL represents still a controversial issue. Herein, the purpose of this study is to update the two previous meta-analyses to evaluate the efficacy and safety
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of PCNL with the patient in the prone versus supine position.
Methods
Urolithiasis (2014) 42:87–93
free rate, complications, the length of hospital stay, and operative time. We divided patients into supine and prone groups according to patients’ position in PCNL. The primary outcome was the stone-free rate, followed by operative time, length of hospital stay, and complication rate as secondary outcomes.
Search strategy and study selection Statistical analysis A literature search of MEDLINE, EMBASE, google scholar, and the Cochrane Central Register of Controlled Trials was performed to identify relevant studies. The search strategy was ‘‘(Nephrostomy, Percutaneous, PCNL, PCN, PNL) [MeSH Terms] AND (supine position OR dorsal decubitus OR dorsal position OR prone position) [Title/Abstract]’’. The search was restricted to human subjects and time up to June, 2013. No language was restricted. Additional manual searches were performed of the reference lists of included studies, reviews and metaanalyses. The following inclusion criteria were used: (1) patients with renal or upper ureteral stones, (2) patients were treated with PCNL in supine versus prone position, (3) outcomes including the efficacy and safety of the PCNL, (4) a randomized controlled trial (RCT) or retrospective comparative study design, and (5) where more than one publication of one study exists, only the publication with the most complete data will be included. The following exclusion criteria were used: (1) the inclusion criteria were not met, (2) pediatric patient population, (3) unclear position of PCNL, or other position and (4) authors of the included studies were contacted wherever the data were unavailable or unclear. If data were not provided or clarified, the study was excluded. The quality of RCT studies was assessed by the Cochrane Collaboration’s tool, which included assessment of sequence generation, allocation concealment, blinding, incomplete outcome data, selective reporting of outcomes, and other possible sources of bias. The non-RCT studies were assessed with a modification of the Newcastle-Ottawa Scale [20]: scores [5 were defined as high quality, and a score \5 as low quality. Two reviewers performed the quality assessment independently. Discrepancy was resolved in consultation with the third reviewer. Data extraction Two reviewers independently extracted data from the included studies, and disagreements were resolved by discussion until a consensus was reached. The following variables were extracted from each study: investigator, date, country of study, position of operation, characteristics of the patients (age, BMI, stone burden, location), stone-
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The meta-analyses were performed using Review Manager (RevMan v.4.2). The weighted mean difference (WMD) and odds ratio (OR) were used to compare continuous and dichotomous variables, respectively. For studies that presented continuous data as median and range values, the standard deviations (SD) were calculated using statistical algorithms described by Hozo et al. [6]. All results were reported with 95 % confidence intervals (CI). Statistical heterogeneity between studies was assessed using the v2 test with significance set at p \ 0.05, and heterogeneity was quantified using the I2 statistic. I2 values of 25, 50, and 75 % correspond to low, medium, and high levels of heterogeneity. A fixed-effect model was used unless statistically significant high heterogeneity(i.e., I2 [ 50 %) existed between studies. A random effects model was used if heterogeneity existed. Sensitivity analysis was performed to explore the influence of low-quality studies. Publication bias was evaluated using a funnel plot.
Results Literature search and characteristics of the included studies We identified 129 studies, of which 71 were excluded because of irrelevance based on the titles and 37 excluded because of irrelevance based on the abstracts (Fig. 1). Full manuscripts were evaluated in 21 studies. After reading the full manuscripts, we excluded 12 studies for various reasons according to our exclusion criteria. Finally, 9 studies were included in a pooled meta-analysis [7–15]. Of the 9 included studies, 1 was a prospective non-randomized study [7], 6 were retrospective studies with no randomisation [8–13], and 2 were RCTs [14, 15]. Quality assessment showed that 4 of the 7 non-RCT studies were deemed as high quality, the other as low quality. Although two RCTs were adequate in sequence generation and incomplete outcome data, inadequate in allocation concealment and blinding, because of the limitation of ethics factor and characteristic of surgery studies, they were deemed as high quality. All the 9 studies reported on the patient demographics, stone size, stone-free rate and complications. Six
Urolithiasis (2014) 42:87–93
89
Fig. 1 Flow diagram of studies identified, included, and excluded
Table 1 Trial and preoperative patient characteristics Investigator
Reference
Country
No. of patientsa
No. of proceduresa
Sexa, M/F
Agea, year
BMIa, kg/m2
Stone burdena
Stone locationa, left/right
McCahy
[8]
Australia
36 vs. 36
41 vs. 41
23/13 vs. NA
53.1 vs. 53.4
26.2 vs. 30.13
25.7 vs. 32.6 mm
NA vs. NA
Wang
[11]
China
12 vs. 6
12 vs. 6
8/4 vs. 4/2
43.8 vs. 44.8
24.2 vs. 24.5
33 vs. 36 mm
5/7 vs. 3/3
Sanguedolce
[10]
Spain
52 vs. 65
52 vs. 65
28/24 vs. 41/24
49 vs. 53
27.1 vs. 26
18.1 vs. 20.6 mm
27/25 vs. 35/30
Mazzucchi
[9]
Brazil
12 vs. 30
24 vs. 32
2/10 vs. 12/18
38.3 vs. 49
34.2 vs. 34
11.28 vs. 10.2 cm2
8/16 vs. 12/20
Valdivia
[12]
CROES
4,637 vs. 1,138
4,585 vs. 1,126
2,662/1,975 vs. 594/544
48.8 vs. 51.0
26.7 vs. 26.6
449.1 vs. 470.6 mm2
NA vs. NA
Falahatkar
[15]
Iran
40 vs. 40
40 vs. 40
18/22 vs. 23/17
43.2 vs. 45.35
26.3 vs. 25.6
40.3 vs. 40.6 mm
16/24 vs. 15/25
Sio
[14]
Italy
36 vs. 39
36 vs. 39
16/20 vs. 17/22
41 vs. 38
26 vs. 28
33 vs. 34 mm
17/19 vs. 19/20
Sesmero
[13]
Spain
54 vs. 50
51 vs. 47
30/24 vs. 23/27
53.9 vs. 54.1
NA vs. NA
416 vs. 399 mm2
24/30 vs. 24/26
Shoma
[7]
Egypt
77 vs. 53
77 vs. 53
43/34 vs. 34/19
47.4 vs. 43.6
NA vs. NA
NA vs. NA
44/33 vs. 26/27
NA Not available, CROES Research Office of the Endourological Society a
The data for the prone versus supine position are given, respectively
studies reported on the operative time and the length of hospital stay. A total of 6,413 patients were included, 4,956 patients in the prone group and 1,457 patients in the supine group. Table 1 shows the study characteristics of the 9 studies. Baseline information seems comparable between supine and prone position groups.
Meta-analysis results Analysis results showed were as follows: 1.
Stone-free rate In meta-analysis of 9 studies, the stonefree rate was 77.3 % (3,804/4,918) in the prone
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90
Urolithiasis (2014) 42:87–93
Fig. 2 Forest plots of outcomes: a stone-free rate, b operative time, c complication, d hospital stay
2.
position versus 72.9 % (1,057/1,449) in the supine position (OR: 1.36; 95 % CI 1.19–1.56; p \ 0.0001), indicating that there was a significantly higher stonefree rate in the prone position than in the supine position (Fig. 2a). Operative time Six studies including 6,102 patients reported on the operative time for PCNL in both
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3.
positions. Meta-analysis demonstrated a shorter operative time in the supine position than in the prone position (WMD: 21.7; 95 % CI 2.46–40.94; p = 0.03) (Fig. 2c). Hospital stay Six studies including 6,102 patients reported on the length of hospital stay for PCNL in both positions. No statistically significant difference
Urolithiasis (2014) 42:87–93
91
Fig. 3 Funnel plot of stone-free rate
4.
was found between the two groups (WMD = 0.05; 95 % CI -0.16–0.25; p = 0.66) (Fig. 2c). Complication rate In meta-analysis of 9 studies, the complication rate was 20.3 % (1,001/4,901) in the prone position versus 18.3 % (266/1,442) in the supine position, showing that both positions had similar complication rates (OR: 1.1; 95 % CI 0.94–1.28; p = 0.24) (Fig. 2d).
Sensitivity analysis When small numbered cohorts were removed [11], there were still no difference between the two groups regarding complication rate (OR: 1.07; 95 % CI 0.92–1.25; p = 0.37), or length of hospital stay (WMD = 0.06; 95 % CI -0.14–0.27; p = 0.54). However, the prone group still had a significantly higher stone-free rate than the supine group (OR: 1.36; 95 % CI 1.19–1.56; p \ 0.0001), while the supine group still had a significantly shorter operative time than the prone group (WMD: 21.7; 95 % CI 2.46–40.94; p = 0.03), which was similar to the general analysis. Publication bias analyses We analyzed possible publication bias by generating funnel plots of the studies used for all of the evaluated comparisons of outcomes. No clear bias was apparent. As an example, we present the funnel plot of stone-free rate showing no obvious asymmetry (Fig. 3). Discussion Two previous meta-analyses [4, 5], both of which were based on 4 studies involving 182 renal units of supine
position and 207 renal units of prone position, showed equivalency for stone-free rate, length of hospital stay and complication rate between prone and supine position, and found shorter operative time in the supine position than in the prone position. In present study, we included 9 studies involving 4,918 renal units of prone position and 1,449 renal units of supine position, and found similar results from the two previous meta-analyses regarding operative time, complication rate and length of hospital stay. However, in terms of stone-free rate, we found that there was a significantly higher stone-free rate in the prone position than in the supine position, which was different to the two previous meta-analyses results. The reasons why our study have found different results comparing with the two previous meta-analyses might be found in the following: Firstly, both of the two previous meta-analyses were only based on 4 studies with small sample size (182 for supine group and 207 for prone group), but our meta-analysis was based on 9 studies with larger sample size. Secondly, different studies had different methods to assess stone-free rate. Thus, the data obtained were not homogenous. The reasons why PCNL in the prone position have higher stone-free rate than that in the supine position may be attributed to the following: due to the effects of gravity on the irrigating fluid, and an unrestricted range of movement for the nephroscope, the prone position are easier access to the renal upper pole calices, a more distended collecting system for better vision, therefore, better clearance of stones [16, 17]. In contrast, supine PCNL have a more difficult nephroscopy because of decreased filling of the collecting system [18]. Consequently, the collecting system is constantly collapsed, and as a result, the surgical filed is relatively small for nephroscopic maneuvers [19]. The supine position also allows limited space for planning renal access, as the flank is relatively poorly exposed and
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may result in reduced ability to maneuver the nephroscope, especially for anterior calyceal calculi. Our pooled analysis and two previous meta-analyses for operative time showed that PCNL in the supine position has significantly shorter operative time than that in prone position. We believe that the majority of the time saving is from not having to reposition the patient from the lithotomy to the prone position with consequent reprepping, redraping, and staff rescrubbing and regowning. There is also some time saved with the ability to perform simultaneous retrograde and caliceal puncture using two surgeons, and less requirement for repeated nephroscope insertion [15]. For complications rate and hospital stay, regardless of our pooled analysis or two previous meta-analyses, the results were similar between the two groups. These data suggested that the PCNL in the supine position was safe. Although the supine position was as safe as the prone position, and has shorter operative time than the prone position, this approach had some disadvantages; for instance, collapse of the collecting system, difficulty in nephroscopy and in approaching the upper calix, and small surgical field for nephroscopy. These limitations may result in lower stone-free rate. Therefore, certain recommendations can be made based on the results. The supine position should be used in patients with cardiovascular risk or patients who cannot tolerate long-time procedures because these patients are not likely to tolerate the hemodynamic effects of anesthesia in the prone position, and the procedure should been completed in short time as soon as possible in order to reduce risk of anesthesia or related risk of operation. On the contrary, the prone position is recommended in patients without these risks because of the prone position having high stone-free rate. The present meta-analysis has some limitations that must be considered. The main limitation is that there were just two RCTs, and most of the included studies were nonRCT studies. In addition, another limitation of this study was that the data obtained were not homogenous because different studies had different methods to assess stone-free rate and operative time. This may potentially have resulted in a lack of a unified reporting methodology. Despite these limitations, our study has large sample size through precise search strategy to include all of the studies related to PCNL in a comparison between supine position and prone position. Furthermore, to reduce the confounding, limit the bias, and draw a scientific and statistically robust conclusion, sensitivity analysis was preformed. In conclusion, the present study found different results from the two previous meta-analyses results regarding stone-free rate; PCNL in the supine position had a significantly lower stone-free rate than that in prone position.
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Urolithiasis (2014) 42:87–93 Conflict of interest interest.
The authors declare that there is no conflict of
References 1. Fernstro¨m I, Johansson B (1976) Percutaneous pyelolithotomy. A new extraction technique. Scand J Urol Nephrol 10(3):257–259 2. Ibarluzea G, Scoffone CM, Cracco CM et al (2007) Supine Valdivia and modified lithotomy position for simultaneous anterograde and retrograde endourological access. BJU Int 100(1):233–236 3. Duty B, Okhunov Z, Smith A, Okeke Z (2011) The debate over percutaneous nephrolithotomy positioning: a comprehensive review. J Urol 186(1):20–25 4. Liu L, Zheng S, Xu Y, Wei Q (2010) Systematic review and meta-analysis of percutaneous nephrolithotomy for patients in the supine versus prone position. J Endourol 24(12):1941–1946 5. Wu P, Wang L, Wang K (2011) Supine versus prone position in percutaneous nephrolithotomy for kidney calculi: a meta-analysis. Int Urol Nephrol 43(1):67–77 6. Hozo SP, Djulbegovic B, Hozo I (2005) Estimating the mean and variance from the median, range, and the size of a sample. BMC Med Res Methodol 20(5):13 7. Shoma AM, Eraky I, El-Kenawy MR, El-Kappany HA (2002) Percutaneous nephrolithotomy in the supine position: technical aspects and functional outcome compared with the prone technique. Urology 60(3):388–392 8. McCahy P, Rzetelski-West K, Gleeson J (2013) Complete stone clearance using a modified supine position: initial experience and comparison with prone percutaneous nephrolithotomy. J Endourol 27(6):705–709 9. Mazzucchi E, Vicentini FC, Marchini GS, Danilovic A, Brito AH, Srougi M (2012) Percutaneous nephrolithotomy in obese patients: comparison between the prone and total supine position. J Endourol 26(11):1437–1442 10. Sanguedolce F, Breda A, Millan F, et al (2012) Lower pole stones: prone PCNL versus supine PCNL in the international cooperation in endourology (ICE) group experience. World J Urol 11. Wang Y, Hou Y, Jiang F, Wang Y, Wang C (2012) Percutaneous nephrolithotomy for staghorn stones in patients with solitary kidney in prone position or in completely supine position: a single-center experience. Int Braz J Urol 38(6):788–794 12. Valdivia JG, Scarpa RM, Duvdevani M et al (2011) Supine versus prone position during percutaneous nephrolithotomy: a report from the clinical research office of the endourological society percutaneous nephrolithotomy global study. J Endourol 25(10):1619–1625 13. Amo´n Sesmero JH, Del Valle Gonza´lez N, Conde Redondo C et al (2008) Comparison between valdivia position and prone position in percutaneous nephrolithotomy. Actas Urol Esp 32(4):424–429 14. De Sio M, Autorino R, Quarto G et al (2008) Modified supine versus prone position in percutaneous nephrolithotomy for renal stones treatable with a single percutaneous access: a prospective randomized trial. Eur Urol 54(1):196–202 15. Falahatkar S, Moghaddam AA, Salehi M, Nikpour S, Esmaili F, Khaki N (2008) Complete supine percutaneous nephrolithotripsy comparison with the prone standard technique. J Endourol 22(11):2513–2517 16. Miano R, Scoffone C, De Nunzio C et al (2010) Position: prone or supine is the issue of percutaneous nephrolithotomy. J Endourol 24(6):931–938
Urolithiasis (2014) 42:87–93 17. de la Rosette JJ, Tsakiris P, Ferrandino MN, Elsakka AM, Rioja J, Preminger GM (2008) Beyond prone position in percutaneous nephrolithotomy: a comprehensive review. Eur Urol 54(6): 1262–1269 18. Autorino R, Giannarini G (2008) Prone or supine: is this the question? Eur Urol 54(6):1216–1218 19. Falahatkar S, Asli MM, Emadi SA, Enshaei A, Pourhadi H, Allahkhah A (2011) Complete supine percutaneous nephrolithotomy
93 (csPCNL) in patients with and without a history of stone surgery: safety and effectiveness of csPCNL. Urol Res 39(4):295–301 20. Wells G, Shea B, O’Connell D, et al The Newcastle-Ottawa Scale (NOS) for assessing the quality of nonrandomized studies in meta-analyses. Ottawa Health Research Institute Web site. http:// www.ohri.ca/programs/clinical_epidemiology/oxford.htm
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ORIGINAL PAPER
Is the supine position superior to the prone position for percutaneous nephrolithotomy (PCNL)? Xiaohua Zhang • Leilei Xia • Tianyuan Xu • Xianjin Wang • Shan Zhong • Zhoujun Shen
Received: 25 July 2013 / Accepted: 12 October 2013 / Published online: 20 October 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract The objective of this study is to update the two previous meta-analyses in order to evaluate the efficacy and safety of percutaneous nephrolithotomy (PCNL) for patients in the prone position versus supine position. An electronic database search of MEDLINE, EMBASE, google scholar, and the Cochrane library was performed up to June, 2013. All studies comparing prone with supine position for PCNL were included. The outcome measures were stone-free rate, operative time, complication and hospital stay. Two randomized controlled trials (RCTs) and 7 non-RCTs, including 6,413 patients (4,956 patients in the prone position group and 1,457 patients in the supine position group), met the inclusion criteria. Meta-analysis of extractable data showed that PCNL in the supine position was associated with a significantly shorter operative time (WMD: 21.7; 95 % CI 2.46–40.94; p = 0.03) but lower stone-free rate (OR: 1.36; 95 % CI 1.19–1.56; p \ 0.0001) than PCNL in the prone position. There was no difference between the two positions regarding hospital stay (WMD = 0.05; 95 % CI -0.16–0.25; p = 0.66) and complication rate (OR: 1.1; 95 % CI 0.94–1.28; p = 0.24). In conclusion, the present study found different results from the two previous meta-analyses results regarding stone-free rate; PCNL in the supine position had a significantly lower stone-free rate than that in prone position. Keywords Percutaneous nephrolithotomy PCNL Prone Supine X. Zhang and L. Xia contributed equally to this work. X. Zhang L. Xia T. Xu X. Wang S. Zhong Z. Shen (&) Department of Urology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, 197 Ruijin No. 2 Road, Shanghai 200025, China e-mail: [email protected]
Introduction Since the first successful stone extraction through a nephrostomy in 1976 [1], percutaneous nephrolithotomy (PCNL) has became the preferred procedure for the treatment of renal stones, especially for large, complex and staghorn calculi. For decades, this technique has been performed in the prone position. More recently, particular interest has been focused on supine position because as compared to the prone position, the supine position has the following advantages [2]: safer and easier for the patient; less cardiovascular change; no need for patient repositioning (with less operative time and less relevant risk of nervous system injuries); and more comfortable and less radiation exposure to the surgeon; but also allows a simultaneous PCNL and ureteroscopy. Despite the potential advantages, the supine position necessitates more lateral displacement of the renal puncture site than the prone position, which may increase the possibility of visceral injuries and cause trauma to intrarenal vessels [3]. Therefore, controversy has emerged as to which is the better position for PCNL. Two very recent meta-analyses comparing supine versus prone position for PCNL have been published [4, 5], both of which were based on 4 publications that met their inclusion criteria—2 prospective RCTs and 2 case control studies. Both meta-analyses concluded that the two positions showed equivalency for stone-free rate, length of hospital stay, and complication rate. In addition, both found supine PCNL had shorter operative time than prone PCNL. Despite these two meta-analyses published, many studies have been published in the literature from then and yielded inconsistent results. The best access to PCNL represents still a controversial issue. Herein, the purpose of this study is to update the two previous meta-analyses to evaluate the efficacy and safety
123
88
of PCNL with the patient in the prone versus supine position.
Methods
Urolithiasis (2014) 42:87–93
free rate, complications, the length of hospital stay, and operative time. We divided patients into supine and prone groups according to patients’ position in PCNL. The primary outcome was the stone-free rate, followed by operative time, length of hospital stay, and complication rate as secondary outcomes.
Search strategy and study selection Statistical analysis A literature search of MEDLINE, EMBASE, google scholar, and the Cochrane Central Register of Controlled Trials was performed to identify relevant studies. The search strategy was ‘‘(Nephrostomy, Percutaneous, PCNL, PCN, PNL) [MeSH Terms] AND (supine position OR dorsal decubitus OR dorsal position OR prone position) [Title/Abstract]’’. The search was restricted to human subjects and time up to June, 2013. No language was restricted. Additional manual searches were performed of the reference lists of included studies, reviews and metaanalyses. The following inclusion criteria were used: (1) patients with renal or upper ureteral stones, (2) patients were treated with PCNL in supine versus prone position, (3) outcomes including the efficacy and safety of the PCNL, (4) a randomized controlled trial (RCT) or retrospective comparative study design, and (5) where more than one publication of one study exists, only the publication with the most complete data will be included. The following exclusion criteria were used: (1) the inclusion criteria were not met, (2) pediatric patient population, (3) unclear position of PCNL, or other position and (4) authors of the included studies were contacted wherever the data were unavailable or unclear. If data were not provided or clarified, the study was excluded. The quality of RCT studies was assessed by the Cochrane Collaboration’s tool, which included assessment of sequence generation, allocation concealment, blinding, incomplete outcome data, selective reporting of outcomes, and other possible sources of bias. The non-RCT studies were assessed with a modification of the Newcastle-Ottawa Scale [20]: scores [5 were defined as high quality, and a score \5 as low quality. Two reviewers performed the quality assessment independently. Discrepancy was resolved in consultation with the third reviewer. Data extraction Two reviewers independently extracted data from the included studies, and disagreements were resolved by discussion until a consensus was reached. The following variables were extracted from each study: investigator, date, country of study, position of operation, characteristics of the patients (age, BMI, stone burden, location), stone-
123
The meta-analyses were performed using Review Manager (RevMan v.4.2). The weighted mean difference (WMD) and odds ratio (OR) were used to compare continuous and dichotomous variables, respectively. For studies that presented continuous data as median and range values, the standard deviations (SD) were calculated using statistical algorithms described by Hozo et al. [6]. All results were reported with 95 % confidence intervals (CI). Statistical heterogeneity between studies was assessed using the v2 test with significance set at p \ 0.05, and heterogeneity was quantified using the I2 statistic. I2 values of 25, 50, and 75 % correspond to low, medium, and high levels of heterogeneity. A fixed-effect model was used unless statistically significant high heterogeneity(i.e., I2 [ 50 %) existed between studies. A random effects model was used if heterogeneity existed. Sensitivity analysis was performed to explore the influence of low-quality studies. Publication bias was evaluated using a funnel plot.
Results Literature search and characteristics of the included studies We identified 129 studies, of which 71 were excluded because of irrelevance based on the titles and 37 excluded because of irrelevance based on the abstracts (Fig. 1). Full manuscripts were evaluated in 21 studies. After reading the full manuscripts, we excluded 12 studies for various reasons according to our exclusion criteria. Finally, 9 studies were included in a pooled meta-analysis [7–15]. Of the 9 included studies, 1 was a prospective non-randomized study [7], 6 were retrospective studies with no randomisation [8–13], and 2 were RCTs [14, 15]. Quality assessment showed that 4 of the 7 non-RCT studies were deemed as high quality, the other as low quality. Although two RCTs were adequate in sequence generation and incomplete outcome data, inadequate in allocation concealment and blinding, because of the limitation of ethics factor and characteristic of surgery studies, they were deemed as high quality. All the 9 studies reported on the patient demographics, stone size, stone-free rate and complications. Six
Urolithiasis (2014) 42:87–93
89
Fig. 1 Flow diagram of studies identified, included, and excluded
Table 1 Trial and preoperative patient characteristics Investigator
Reference
Country
No. of patientsa
No. of proceduresa
Sexa, M/F
Agea, year
BMIa, kg/m2
Stone burdena
Stone locationa, left/right
McCahy
[8]
Australia
36 vs. 36
41 vs. 41
23/13 vs. NA
53.1 vs. 53.4
26.2 vs. 30.13
25.7 vs. 32.6 mm
NA vs. NA
Wang
[11]
China
12 vs. 6
12 vs. 6
8/4 vs. 4/2
43.8 vs. 44.8
24.2 vs. 24.5
33 vs. 36 mm
5/7 vs. 3/3
Sanguedolce
[10]
Spain
52 vs. 65
52 vs. 65
28/24 vs. 41/24
49 vs. 53
27.1 vs. 26
18.1 vs. 20.6 mm
27/25 vs. 35/30
Mazzucchi
[9]
Brazil
12 vs. 30
24 vs. 32
2/10 vs. 12/18
38.3 vs. 49
34.2 vs. 34
11.28 vs. 10.2 cm2
8/16 vs. 12/20
Valdivia
[12]
CROES
4,637 vs. 1,138
4,585 vs. 1,126
2,662/1,975 vs. 594/544
48.8 vs. 51.0
26.7 vs. 26.6
449.1 vs. 470.6 mm2
NA vs. NA
Falahatkar
[15]
Iran
40 vs. 40
40 vs. 40
18/22 vs. 23/17
43.2 vs. 45.35
26.3 vs. 25.6
40.3 vs. 40.6 mm
16/24 vs. 15/25
Sio
[14]
Italy
36 vs. 39
36 vs. 39
16/20 vs. 17/22
41 vs. 38
26 vs. 28
33 vs. 34 mm
17/19 vs. 19/20
Sesmero
[13]
Spain
54 vs. 50
51 vs. 47
30/24 vs. 23/27
53.9 vs. 54.1
NA vs. NA
416 vs. 399 mm2
24/30 vs. 24/26
Shoma
[7]
Egypt
77 vs. 53
77 vs. 53
43/34 vs. 34/19
47.4 vs. 43.6
NA vs. NA
NA vs. NA
44/33 vs. 26/27
NA Not available, CROES Research Office of the Endourological Society a
The data for the prone versus supine position are given, respectively
studies reported on the operative time and the length of hospital stay. A total of 6,413 patients were included, 4,956 patients in the prone group and 1,457 patients in the supine group. Table 1 shows the study characteristics of the 9 studies. Baseline information seems comparable between supine and prone position groups.
Meta-analysis results Analysis results showed were as follows: 1.
Stone-free rate In meta-analysis of 9 studies, the stonefree rate was 77.3 % (3,804/4,918) in the prone
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Fig. 2 Forest plots of outcomes: a stone-free rate, b operative time, c complication, d hospital stay
2.
position versus 72.9 % (1,057/1,449) in the supine position (OR: 1.36; 95 % CI 1.19–1.56; p \ 0.0001), indicating that there was a significantly higher stonefree rate in the prone position than in the supine position (Fig. 2a). Operative time Six studies including 6,102 patients reported on the operative time for PCNL in both
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3.
positions. Meta-analysis demonstrated a shorter operative time in the supine position than in the prone position (WMD: 21.7; 95 % CI 2.46–40.94; p = 0.03) (Fig. 2c). Hospital stay Six studies including 6,102 patients reported on the length of hospital stay for PCNL in both positions. No statistically significant difference
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Fig. 3 Funnel plot of stone-free rate
4.
was found between the two groups (WMD = 0.05; 95 % CI -0.16–0.25; p = 0.66) (Fig. 2c). Complication rate In meta-analysis of 9 studies, the complication rate was 20.3 % (1,001/4,901) in the prone position versus 18.3 % (266/1,442) in the supine position, showing that both positions had similar complication rates (OR: 1.1; 95 % CI 0.94–1.28; p = 0.24) (Fig. 2d).
Sensitivity analysis When small numbered cohorts were removed [11], there were still no difference between the two groups regarding complication rate (OR: 1.07; 95 % CI 0.92–1.25; p = 0.37), or length of hospital stay (WMD = 0.06; 95 % CI -0.14–0.27; p = 0.54). However, the prone group still had a significantly higher stone-free rate than the supine group (OR: 1.36; 95 % CI 1.19–1.56; p \ 0.0001), while the supine group still had a significantly shorter operative time than the prone group (WMD: 21.7; 95 % CI 2.46–40.94; p = 0.03), which was similar to the general analysis. Publication bias analyses We analyzed possible publication bias by generating funnel plots of the studies used for all of the evaluated comparisons of outcomes. No clear bias was apparent. As an example, we present the funnel plot of stone-free rate showing no obvious asymmetry (Fig. 3). Discussion Two previous meta-analyses [4, 5], both of which were based on 4 studies involving 182 renal units of supine
position and 207 renal units of prone position, showed equivalency for stone-free rate, length of hospital stay and complication rate between prone and supine position, and found shorter operative time in the supine position than in the prone position. In present study, we included 9 studies involving 4,918 renal units of prone position and 1,449 renal units of supine position, and found similar results from the two previous meta-analyses regarding operative time, complication rate and length of hospital stay. However, in terms of stone-free rate, we found that there was a significantly higher stone-free rate in the prone position than in the supine position, which was different to the two previous meta-analyses results. The reasons why our study have found different results comparing with the two previous meta-analyses might be found in the following: Firstly, both of the two previous meta-analyses were only based on 4 studies with small sample size (182 for supine group and 207 for prone group), but our meta-analysis was based on 9 studies with larger sample size. Secondly, different studies had different methods to assess stone-free rate. Thus, the data obtained were not homogenous. The reasons why PCNL in the prone position have higher stone-free rate than that in the supine position may be attributed to the following: due to the effects of gravity on the irrigating fluid, and an unrestricted range of movement for the nephroscope, the prone position are easier access to the renal upper pole calices, a more distended collecting system for better vision, therefore, better clearance of stones [16, 17]. In contrast, supine PCNL have a more difficult nephroscopy because of decreased filling of the collecting system [18]. Consequently, the collecting system is constantly collapsed, and as a result, the surgical filed is relatively small for nephroscopic maneuvers [19]. The supine position also allows limited space for planning renal access, as the flank is relatively poorly exposed and
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may result in reduced ability to maneuver the nephroscope, especially for anterior calyceal calculi. Our pooled analysis and two previous meta-analyses for operative time showed that PCNL in the supine position has significantly shorter operative time than that in prone position. We believe that the majority of the time saving is from not having to reposition the patient from the lithotomy to the prone position with consequent reprepping, redraping, and staff rescrubbing and regowning. There is also some time saved with the ability to perform simultaneous retrograde and caliceal puncture using two surgeons, and less requirement for repeated nephroscope insertion [15]. For complications rate and hospital stay, regardless of our pooled analysis or two previous meta-analyses, the results were similar between the two groups. These data suggested that the PCNL in the supine position was safe. Although the supine position was as safe as the prone position, and has shorter operative time than the prone position, this approach had some disadvantages; for instance, collapse of the collecting system, difficulty in nephroscopy and in approaching the upper calix, and small surgical field for nephroscopy. These limitations may result in lower stone-free rate. Therefore, certain recommendations can be made based on the results. The supine position should be used in patients with cardiovascular risk or patients who cannot tolerate long-time procedures because these patients are not likely to tolerate the hemodynamic effects of anesthesia in the prone position, and the procedure should been completed in short time as soon as possible in order to reduce risk of anesthesia or related risk of operation. On the contrary, the prone position is recommended in patients without these risks because of the prone position having high stone-free rate. The present meta-analysis has some limitations that must be considered. The main limitation is that there were just two RCTs, and most of the included studies were nonRCT studies. In addition, another limitation of this study was that the data obtained were not homogenous because different studies had different methods to assess stone-free rate and operative time. This may potentially have resulted in a lack of a unified reporting methodology. Despite these limitations, our study has large sample size through precise search strategy to include all of the studies related to PCNL in a comparison between supine position and prone position. Furthermore, to reduce the confounding, limit the bias, and draw a scientific and statistically robust conclusion, sensitivity analysis was preformed. In conclusion, the present study found different results from the two previous meta-analyses results regarding stone-free rate; PCNL in the supine position had a significantly lower stone-free rate than that in prone position.
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Urolithiasis (2014) 42:87–93 Conflict of interest interest.
The authors declare that there is no conflict of
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