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Volume 54, issue 6, pages 1209-1454, December 2008Reviews
Beyond Prone Position in Percutaneous Nephrolithotomy: A Comprehensive Review
Jean J.M.C.H. de la Rosette a 
, Peter Tsakiris a, Michael N. Ferrandino b, Ahmed M. Elsakka a, Jorge Rioja a, Glenn M. Preminger b.
Accepted 4 August 2008, Published online 12 August 2008, pages 1262 - 1269
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Abstract
Context
Percutaneous nephrolithotomy (PNL) is traditionally performed with the patient in the prone position.
Objective
To assess the efficacy and safety of the prone and supine positions, particularly in obese patients and in those with staghorn calculi.
Evidence acquisition
A Medline search was conducted for articles published during the last 10 yr related to PNL in the prone and supine positions.
Evidence synthesis
This search revealed 9 published studies for supine and 25 for prone PNL. None of the supine PNL studies reported visceral injuries, while transfusion rates were 0.0–9.4% and stone-free rates were 69.6–95.0%. One study of supine PNL evaluated a significant proportion of obese patients. Prone PNL studies in obese patients report transfusion rates of 3.2–8.8% and stone-free rates of 79.0–89.2%.
In the only randomized study, excluding obese patients and staghorn calculi, operative time favors the supine position. A nonrandomized comparative study demonstrated similar complication rates with insignificant improvement in treatment success for supine PNL; however, when comparing series with similar proportions of staghorn calculi cases, there are slightly improved outcomes for prone PNL. Moreover, comparison of weighted means favors prone PNL.
Conclusions
For obese patients and staghorn calculi, prone PNL appears to be associated with decreased operative times with similar bleeding rates and slightly better stone-free rates than supine PNL.
Keywords: Percutaneous nephrolithotomy, Prone position, Supine position, Obesity, Calculi.
Article Outline
1. Introduction
Currently, percutaneous nephrolithotomy (PNL) is the treatment of choice for large renal stones, staghorn calculi, stones resistant to fragmentation, or stones occurring in kidneys with an abnormal anatomy [1], and [2]. The safety and efficacy of PNL for the treatment of more complex stones and its use in more diverse patient populations, combined with the growing incidence of stone disease, likely explains the increasing use of PNL for stone management over the last 10 yr, as indicated by recent studies [3], [4], and [5].
Traditionally, PNL has been performed in the prone position [6], and the morbidity of the procedure has been well documented [7]. Ten years ago, Valdivia et al first described PNL in the supine position, advocating several benefits for the patients, especially in those at higher anesthesiologic risk [8]. Since then, several other investigators have reported their experience with this technique [9], [10], [11], [12], [13], [14], [15], and [16]. On the other hand, it has been pointed out that the supine position has its own flaws, such as compromised ventilation in markedly obese patients and a prolonged operative time in the case of larger stones. The aim of this review is to assess the efficacy and safety of PNL in both prone and supine positions, particularly for obese patients and those with staghorn calculi.
2. Evidence acquisition
A Medline search was conducted for articles published during the last 10 yr related to percutaneous nephrolithotomy in supine and prone position. This period was selected because 10 yr have passed since the pioneering paper by Valdivia et al [8]. The terms used for the search included: percutaneous nephrolithotomy, PNL, prone, supine, obese, staghorn calculi, outcomes, complications. In total, 34 papers were produced by the search; based on the criteria for evaluation mentioned above, 13 were selected. To optimize quality assessment, three authors independently selected from the search the manuscripts included in this review. Only original articles were selected; non-English articles, letters to the editor, and published abstracts were excluded. Outcome measures for PNL success included stone-free rate, transfusion rate, organ injury, hospital admission, and operative time. It is important to acknowledge that there are no manuscripts for supine and prone PNL conducted in solely obese or morbidly obese patients or staghorn calculi. Moreover, sometimes difficulties in data analysis were encountered, such as the extrapolation of outcome measures, including “successful treatment.” The authors feel, though, that these limitations do not jeopardize the validity of the present work. Weighted means in obese patients and staghorn calculi were calculated separately for each position and then compared.
3. Evidence synthesis
The evidence synthesis is divided into four subsections: morbidity and operative time, treatment success, advantages, and limitations.
3.1. Morbidity and operative time
The overall outcomes in normal-sized patients of the series with PNL in the supine position are similar to the outcomes of the classical prone position. Interestingly, there have not been any visceral injuries reported with supine PNL. It has been suggested that the more anterior displacement of the colon in the supine compared to the prone position may result in the lack of colonic injury. Both LeRoy et al and Hopper et al found only 2% of the patients had a retrorenal colon when supine, which subsequently increased to 10% when prone [17], and [18]. In 83.0–98.0% of the cases, lower- or middle-pole calyceal-puncture PNL was performed, and one PNL session was adequate to treat 85.0–92.5% of the patients. Bleeding requiring transfusion is reported in 0.0–9.4% of cases, and successful treatment is documented in 69.6–95.0% of cases (Table 1).
Table 1 All published case series of percutaneous nephrolithotomy in the supine position
| Valdivia et al 1998 [8] | Shoma et al 2002 [9] | Ng et al 2004 [10] | Manohar et al 2007 [11] | Neto et al 2007 [12] | Zhou et al 2008 [13] | Rana et al 2008 [14] | De Sio et al 2008 [15] | Steele et al 2007 [16] | |
|---|---|---|---|---|---|---|---|---|---|
| Puncture guidance | FL | FL | U/S + FL | U/S + FL | FL* | U/S + FL | FL | FL | FL |
| Body mass characteristics | Morbidly obese = 7 | Mean weight = 78.5 | – | Mean BMI = 24 | – | Mean weight = 62 | Mean weight = 62 | BMI < 30 | Mean weight = 82 |
| BMI > 40 = 11% | |||||||||
| Number of patients | 520 of 557 | 53 | 62 | 62 | 88 | 92 | 184 | 39 | 322 |
| ASA classification | ≥III = 12.5% | – | – | III = 69% | – | – | – | – | – |
| IV = 24% | |||||||||
| Operation time (min) | 85 | – | – | 74 | 162 | 120 | 65 | 43 | – |
| Bleeding requiring transfusion | 1.4% | 9.4% | 4.8% | 3.2% | 8.0% | 1.1% | 3.8% | 0.0% | 3.7% |
| Visceral injury | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0% |
| Staghorn calculi | – | 3 (6.0%) | 10 (16.1%) | 7 (11.3%) | 26 (29.5%) | 19 (20.6%) | 39 (20.0%) | 0 (0.0%) | 33 (10.2%) |
| Lower- or middle-pole access | 97% | 87% | 98% | 92% | 83% | – | 97% | 100% | – |
| Single procedure | – | 92.5% | – | 85.0% | 88.6% | 83.0% | 94.0% | – | – |
| Success rate | – | 89.0% (<4 mm) | 76.0% (undefined) | 95.0% (<4 mm) | 70.5% (<5 mm) | 69.6% | 84.0% | 88.7% (<2 mm) | 91.0% |
FL = fluoroscopic; U/S = ultrasound; * = placed by radiologist; ASA = American Society of Anesthesiologists; – = not mentioned.
Four studies using supine access indicate body mass characteristics of treated patients [8], [9], [11], and [15]. Only Manohar et al includes a patient population with a significant proportion of obese or morbidly obese patients [11]. Eleven percent of the patients had a body mass index (BMI) >40, while the mean BMI was 24.28. Additionally, the patients treated in this study were patients with comorbidities and compromised general status; 93% had an American Society of Anesthesiologists (ASA) score of 3 or 4. Fever >38 °C was reported in 4% of patients following supine PNL, whereas acute bleeding was higher in the supine group (blood transfusion: prone 4% vs supine 9%) and may be related to the early learning curve by the authors.
Regarding the outcomes of PNL in the prone position for morbidly obese patients, four case series have been published and were selected for this review [19], [20], [21], and [22] (Table 2). Three of the four articles report an operative time ranging from 68.5 to 81.4 min. The remaining study reports an operative time of 181.2 min; however, one-third of the patients were treated for staghorn calculi.
Table 2 Case series of percutaneous nephrolithotomy in the prone position in obese or morbidly obese patients
| Koo et al 2004 [19] | El-Assmy et al 2006 [20] | Pearl et al 1998 [21] | Sergeyev et al 2007 [22] | |||
|---|---|---|---|---|---|---|
| Body mass index | 30–40 | >40 | 30–40 | >40 | >30 | >30 |
| Number of patients | 67 | 12 | 468 | 92 | 57 | 37 |
| ASA classification | >III = 10% | >III = 31% | – | – | II = 59.6% | – |
| III = 40.4% | ||||||
| Staghorn calculi | 6% | 33% | 4.1% | 6.5% | 31.7% | – |
| Operation time (min) | 68.5 | 81.4 | 68.5 | 77.2 | 181.2 | – |
| Bleeding requiring transfusion | – | – | 3.2% | 3.2% | 8.8% | Mean Hb loss = 2.29 |
| Hospital stay | 6.1 | 5.8 | 3.3 | 3.1 | 4.9 | 3.7 |
| Stone free | 79% | 83% | 84.8% | 84.7% | Overall = 88.3% | 89.2% |
| Staghorn = 84.2% | ||||||
ASA = American Society of Anesthesiologists; Hb = hemoglobin; (–) = not mentioned.
Transfusion rates ranged from 3.2 to 8.8%, while mean hospital stay was 3.1 to 6.1 d. The studies that stratified the patients according to BMI demonstrated that there were no statistically significant differences in operative duration, decrease in hemoglobin concentration, hospital stay, and stone-free rates among all patient groups [19], and [20]. In general, the duration of the operation and treatment success rates are concordant for both positions (Fig. 1).
00950-0/assets/gr1.jpg)
Fig. 1
Comparison of operative time and treatment success between prone and supine percutaneous nephrolithotomy.
BMI = body mass index.
3.2. Treatment success
To investigate if the supine is more favorable than the prone approach, a randomized study should be conducted. Such a study was recently conducted by De Sio et al in a carefully selected patient population with uncomplicated stones and BMI < 30 [15]. No significant difference was ascertained between the two groups in terms of stone-free rate (supine 88.7% vs prone 91.6%), mean blood loss (supine delta hemoglobin –2.3 g/dl vs prone delta hemoglobin 2.2 g/dl), and mean hospital stay (supine 4.3 d vs prone 4.1 d). The only significant difference reported was mean operative time (supine 43 min vs prone 68 min). Another study compared these positions in a nonrandomized prospective analysis [9]. In that study, the preoperative parameters of the two groups were comparable, and the results showed similar complication rates in both groups. A trend toward improved treatment success was identified in favor of the supine group (89% vs 84%), but these results were not statistically significant. We may, therefore, carefully conclude that the outcomes in nonobese patients and with small-sized stones seem to favor the supine approach.
A more objective way to address outcomes in obese patients and with staghorn calculi is to calculate the weighted means for each position separately and compare them (Fig. 2). This comparison reveals significantly less operative time for the prone PNL over supine PNL, with similar bleeding rates and slightly better success rates.
00950-0/assets/gr2.jpg)
Fig. 2 Comparison of weighted means presenting outcomes in supine and prone position on operative time, success rate, and bleeding needing transfusion.
Since both duration of operation and treatment success highly depend on the proportion of complex stones treated, an outcome comparison between the two positions is even more objective when performed with studies that include patients with similar complexity of stones. In an effort to eliminate any differences in the complexity of the treated stones, studies with similar proportions of staghorn calculi treated were selected and compared (Fig. 3). All of these studies report staghorn stones between 29.5% and 31.7% of cases. Though the number of studies meeting these criteria is very limited and conclusions are, therefore, questionable, the available data suggest that the prone position provides better stone-free rates in the group of patients with complex renal calculi.
00950-0/assets/gr3.jpg)
Fig. 3
Success rate of percutaneous nephrolithotomy in studies with similar proportions of staghorn calculi treated (number of patients equals number of patients studied in each paper).
BMI = body mass index.
3.3. Advantages
Traditionally, PNL has been performed in the prone position, as it was initially considered by many to be the safest approach to the kidney [1], [23], [24], and [25]. This position provides posterior access to the collecting system that theoretically enables the surgeon to puncture a posterior calyx through Brodel's avascular renal plane without causing significant parenchymal bleeding, peritoneal perforation, or visceral injuries. The prone PNL approach also provides a large surface area for selection of puncture site and a wide space for instrument manipulation.
The prone position, however, is often associated with restriction of the patient's respiratory movement and, therefore, is not always feasible. Morbid obesity, compromised cardiopulmonary status, and stature deformity provide significant challenges to both the anesthesiologist and the surgeon. In addition, prone positioning does not completely eliminate complications. Large series report a 3–10% rate of acute bleeding requiring transfusion and 0.5% incidence of bowel perforation [17], [26], and [27]. In cases of more complex stones, prone positioning is associated with stone-free rates of 74–83%, while transfusion rates can range from 14–24% [2].
The rising number of PNL procedures combined with increasing confidence and experience has caused researchers to modify the prone PNL technique in an effort to improve results and overcome these limitations. The traditional prone positioning has been challenged and altered by various authors. Available studies demonstrate the safety of more lateral percutaneous nephrostomy placement. These reports utilize sophisticated imaging modalities and have demonstrated a favorable relationship between the nephrostomy tract and the colon or other viscera [28], [29], and [30]. With increased understanding of renal anatomy and related viscera, urologists have altered patient positioning. These alterations include the reverse lithotomy position, the lateral decubitus, and the supine position [31], and [32].
The supine position offers several advantages. Patient positioning is less demanding and time-consuming because a change is not required from the lithotomy to the prone position during the procedure. A supine position is more comfortable for the patient, which might enable the use of decreased anesthetics. The supine position allows for more rapid access to the airway and, therefore, may be less hazardous, especially in patients with compromised cardiopulmonary function or morbid obesity or in those who require a prolonged procedure. Additionally, if required, a more familiar approach for simultaneous ureteroscopic access is readily obtained, allowing combined PNL and ureteroscopy (URS) for management of complex stone disease.
Considering these advantages, the supine positioning of the patient for PNL seems a very attractive option. Published series from different centers have show that supine PNL is safe and has several benefits for the patient and several technical advantages for the surgeon. Because the tract is horizontal or slightly inclined downward, the pressure of the collecting system is very low, which may facilitate the spontaneous evacuation of stone fragments. Some have suggested that this more descendent position of the calyx in relation to the renal pelvis minimizes the possibility of a stone fragment migrating into the ureter during calculus fragmentation [10]. The supine position also allows greater versatility during stone management, since ureteroscopy can readily be performed if there is a contralateral ureteral stone or simultaneous procedures for renal, ureteral, and bladder stones in the same single supine lithotomy position [10]. A final advantage of the supine PNL position is that urologists are more comfortable adopting a sitting posture during stone management.
3.4. Limitations
Limitations of supine PNL include a more difficult nephroscopy because of decreased filling of the collecting system. Consequently, the collecting system is constantly collapsed, and, as a result, the surgical field is relatively small for nephroscopic maneuvers. In addition, an upper-pole calyceal puncture is quite challenging, as the upper pole is more medial and posterior and concealed deeply in the rib cage when the patient is in a supine positioned. Suggested ways to surpass this limitation would be to either tilt the table toward the contralateral side or to perform a simultaneous ureteroscopy [10], and [11].
Theoretically, one would expect that the possible advantages of the supine PNL would be better realized in cases such as compromised patients, the morbidly obese, and patients with staghorn calculi. For this reason, our literature review focused on these patients. Unfortunately, there are no data available for supine PNL conducted solely in obese or morbidly obese patients. It is possible that the acquired experience with prone PNL over the years translates to better outcomes. In this case, a more objective comparison could be done when familiarity and experience in supine PNL has grown. It may also confirm that in these cases, prone access is a better choice because of higher maneuverability of the access sheet and better access to the upper pole.
The current study is somewhat limited due to the lack of available data for review and thus our inability to perform a true meta-analysis. When PNL was initially reported, the prone position was the acceptable method of positioning these patients. The early series by Alken et al, Segura et al, and Smith et al documented the efficacy and safety of this technique [6], [25], and [26]. PNL, therefore, disseminated into urologic practice. In attempts to improve and document increasing indications for PNL, recent literature has concentrated on alternatives in patient positioning, widening patient selection, or new techniques (i.e., tubeless PNL). Most reports are case series and/or do not obtain their results in randomized controlled fashion, thereby limiting the ability to make strong recommendations. Therefore, true randomized prospective studies, which will likely need to be multi-institutional, are needed to most accurately address the future directions of PNL. Moreover, we need to standardize our registration of outcomes and complications to facilitate more accurate comparisons between techniques and treatment strategies in PNL [33]. Finally, adequate training in the different techniques and approaches for PNL is an important issue that deserves our special attention to optimize indications and treatment outcomes [34].
Despite the aforementioned limitations, this study is the first to collect and analyze data on supine versus prone PNL, with special attention to the obese and staghorn calculi patient populations. The only randomized study conducted thus far elegantly presented the argument in favor for the supine approach over the prone approach [15]. The major limitation of this paper, however, is the strict inclusion criteria for this study, allowing only uncomplicated low-risk patients with a small stone load to be included. Since one would expect that more physically compromised patients and patients with staghorn calculi might be especially likely to benefit from a supine approach over a prone approach, we have conducted this study. Although in the present analysis, there is a trend in favor of performing PNL in the prone position, urologists are recommended to perform PNL in the position that is most familiar to them. Supine PNL may be an especially attractive option for a selected group of patients in high anesthetic risk categories with the prone position or in whom simultaneous nephrolithotripsy and demanding ureteroscopic procedures are planned. Further efforts are needed to compare supine and prone positioning for normal healthy individuals as well as for obese or complicated patients.
4. Conclusions
Although the supine position seems to provide theoretical advantages for obese and morbidly obese patients and patients with staghorn calculi, a trend in favor of better outcomes in the prone position over the supine position was identified.
Author contributions: Jean de la Rosette had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: de la Rosette, Tsakiris, Elsakka, Ferrandino, Rioja, Preminger.
Acquisition of data: Elsakka, Tsakiris, Ferrandino.
Analysis and interpretation of data: Tsakiris, Ferrandino, Elsakka, Rioja, Preminger, de la Rosette.
Drafting of the manuscript: Tsakiris, Elsakka, Ferrandino, de la Rosette.
Critical revision of the manuscript for important intellectual content: Preminger, de la Rosette.
Statistical analysis: Elsakka, Tsakiris, Rioja.
Obtaining funding: None.
Administrative, technical, or material support: None.
Supervision: Preminger, de la Rosette.
Other (specify): None.
Financial disclosures: I certify that all conflicts of interest, including specific financial interests and relationships and affiliations relevant to the subject matter or materials discussed in the manuscript (eg, employment/ affiliation, grants or funding, consultancies, honoraria, stock ownership or options, expert testimony, royalties, or patents filed, received, or pending), are the following: None.
Funding/Support and role of the sponsor: None.
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Footnotes
a Department of Urology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
b Comprehensive Kidney Stone Center, Duke University Medical Center, Durham, NC, USA
Corresponding author. Department of Urology G4-105, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Tel. +31 20 566 6030; Fax: +31 20 6669585.
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