Outcomes of Prone and Complete Supine Percutaneous Nephrolithotripsy According to Body Mass Index

ABSTRACT

Introduction: To determine whether body mass index (BMI) can influence the outcomes of percutaneous nephrolithotripsy (PCNL) in the prone and the supine position or cannot.

Materials and Methods: We have reviewed the files of 110 patients who underwent the prone and the complete supine PCNL (csPCNL) between September 2007 and December 2008 in the 3 categories: BMI < 25, 25 > BMI < 30, and BMI > 30.

Results: The demographic data and surgical outcomes of the patients were evaluated. There was no statistically significant difference between groups, except the stone-free rate in the BMI < 25 group, which was higher in the prone position. Moreover, in groups with higher BMIs, the anesthesia time was increased. The overall stone-free rate was 78 and 73.3% in the prone and supine positions, respectively (p = 0.57). No statistically significant differences were found, except a higher incidence of fever in the prone approach and a significantly shorter anesthesia time in the complete supine position.

Conclusion: The outcomes of PCNL in both positions were not dependent on the patient‘s BMI. Also, the anesthesia time was prolonged in patients with a higher BMI. This study showed that the prone and the supine PCNL in obese and morbidly obese patients were safe and effective.


Siavash Falahatkar, Marzieh Akbarpour, Ahmad Enshaei, Samaneh Esmaeili, Amin Afsharimoghaddam

Date Received: January 10, 2012 Accepted on: February 14, 2012


KEYWORDS: Complete supine PCNL, prone PCNL, BMI, stone-free rate, fever, total ultrasonic guidance

CORRESPONDENCE:Siavash Falahatkar, Professor of Urology, Urology Research Center, Razi Hospital, Sardare Jangal Street, Rasht, Gilan Province, Iran ()

CITATION: UroToday Int J. 2012 Apr;5(2):art 12. http://dx.doi.org/10.3834/uij.1944-5784.2012.04.12

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INTRODUCTION

Percutaneous nephrolithotripsy (PCNL) has traditionally been performed on patients in the prone position [1]. Patient discomfort and circulatory and ventilator difficulties, especially in obese patients, are problems of the prone position [2]. The supine position has numerous advantages over the prone position for PCNL. This approach has been neglected by many surgeons [3].

The efficacy and safety of PCNL in the complete supine position (csPCNL) has been shown for patients [4]. The fear of colon injury and a lack of training in educational centers are the main reasons for lack of acceptance of the supine position. Obesity poses a number of problems in the management of stone disease, from diagnosis and imaging to anesthesia and surgery [5]. The potential advantages of csPCNL are: (1) concomitant ureteroscopy, (2) feasibility to change regional anesthesia to general anesthesia, (3) better airway management, and (4) comfortability, especially for patients with cardiopulmonary disease and morbid obesity.

In this study, we present our experience of PCNL to evaluate the efficacy and safety of the prone and the supine positions, particularly in obese patients.

METHODS

We have reviewed the files of 110 consecutive patients who underwent PCNL between September 2007 and December 2008. We have compared the results of csPCNL with traditional procedures. In our medical center, after a randomized study, we have performed all PCNLs in the complete supine position [4]. Preoperatively, we placed a transient ureteral catheter in the lithotomy position for opacification with the rigid cystoscope and attached it to the urethral catheter. Fifty PCNLs were done in the prone position and 60 in the complete supine position (without a rolled towel under the patient‘s flank. There was no change in the position of the leg, and the patients were placed at the bed’s edge).

Percutaneous access was created under fluoroscopic or totally ultrasonic guidance. Inclusion criteria for fluoroscopic guidance PCNL were patients who were all candidates for PCNL (stones were larger than 2 cm or resistant to extracorporeal shockwave lithotripsy [ESWL] and larger than 1.5 cm in the lower calyx). Our inclusion criteria for ultrasonic guidance were the patients with a single pelvic stone, a single calyceal stone, kidneys with stones in the pelvis and the lower calyx, upper ureteral stones (if they were not a candidate for ESWL or TUL), and kidneys with nonradio-opaque stones. In these cases, we have performed complete ultrasound-guided PCNL. The tract was dilated to 28 to 30 Fr with Amplatz dilators (acute dilation) and then an Amplatz sheath was placed. A grasper directly extracted small stones and a pneumatic device fragmented large stones.

Demographic data and stone characteristics between the 2 groups were not significantly different and they are shown in Table 1. Patients were categorized into 3 groups according to the World Health Organization’s (WHO) classification of body mass index (BMI): < 25 kg/m2 (ideal weight), 25 to 30 kg/m2 (overweight), and > 30 kg/m2 (obese and morbidly obese) [6]. We have compared the outcomes of prone and supine PCNL according to BMI in our patients. Before PCNL, urine cultures were obtained, and if positive, appropriate antibiotics were administered. Associated comorbidities included hypertension (HTN), diabetes mellitus (DM), ischemic heart diseases (IHD), congestive heart failure (CHF), and chronic obstructive pulmonary disease (COPD) (Table 1). After PCNL, stone-free status was determined by fluoroscopy at the end of the procedure and KUB and ultrasonography 1 to 14 days after the procedure. We did not use a CT scan to detect stone-free status in our study, which is a restriction.

Stone-free status was defined as residual stones less than 5 mm in diameter, similar to the study performed by Neto et al. [3]. Before surgery, a ureteral catheter was inserted for all patients and tubeless PCNL was done (no nephrostomy tube was placed after the procedure). In the presence of significant renal pelvic perforation, a nephrostomy tube placement would be necessary. At the end of the fluoroscopy procedure, this would be diagnosed by nephroscopy or by extravasation after contrast material injection, or by observing the collection of fluid via ultrasonography, any ureteral obstruction, and any significant residual stones indicating active bleeding and thus suggesting the need for another procedure. An external ureteral catheter was used as a transient catheter, which was attached to the urethral catheter to remove within 1 to 3 days after PCNL. We inserted a double J stent for 4 to 6 weeks in patients with large stone residue, significant perforation of the pelvis, and coincidental endopyelotomy. Stone burden was defined as the maximum diameter of the stone on KUB, ultrasonography, or a CT scan. In this study, the stone-free rate, Hb before and after surgery, blood transfusion rate, fever rate, anesthesia time, complications, and tubeless PCNL (without a nephrostomy tube) rate were evaluated to determine whether BMI can influence the outcome of PCNL in the prone and the supine positions or cannot. The results were analyzed by the use of a t-test and a Chi-square test. We considered p ≤ 0.05 significant.

RESULTS

The study included 24 (48%) males and 26 (52%) females, with a mean age of 43.9 years, in the prone group and 33 (55%) males and 27 (45%) females, with a mean age of 46.35 years, in the complete supine group. Stone burden in the prone group was 39.7 ± 14.7 mm and 38.1 ± 15.8 mm in the supine group. We have done PCNL with multiple tracts in 27 patients. Five patients in the supine group and 4 patients in the prone group had staghorn stones. The mean BMI was 26.47 ± 4.25 kg/m2 and 27.55 ± 5.5 kg/m2 in the prone and the supine positions, respectively. There was no statistically significant difference between the 2 groups (p = 0.40). In the patients with a BMI ≥ 30, the mean BMI was 34.47 kg/m2. Patients and stone characteristics in the prone and the supine position are summarized in Table 1.

There was not any major complication in our patients, but 13 patients (4 in the prone and 9 in the supine position) suffered bleeding, requiring a blood transfusion (Hb dropped under 10 mg/dl). Patients in the prone position experienced a higher incidence of fever (10 in the prone position versus 3 in the supine position; p = 0.015). There was no colon injury, ureteric obstruction, and septicemia in our patients; failed access was reported in 1 patient in the prone group with a BMI > 30. Extravasation was reported in patients with a BMI < 25 and it was the same in both groups (2 patients in the prone and 2 patients in the supine position). The stone-free rate was 78 and 73.3% in the prone and supine positions, respectively, with no significant differences. Transfusion was needed in 8 and 15% of patients in the prone and the supine position, respectively (p = 0.25). The mean anesthesia time was 96.80 ± 29.66 minutes in the prone position versus 79.38 ± 38.38 minutes in the supine position, with a statistically significant difference (p = 0.01). There was no statistically significant difference between the prone and the supine position in hospitalization (54.06 ± 14.34 hours in prone versus 58.33 ± 13.80 hours in supine; p = 0.115). We performed tubeless PCNL for our patients routinely.

One of our patients in the prone group suffered from rheumatoid arthritis (RA) and corticosteroid side effects, such as obesity (BMI = 37.7 kg/m2), HTN, and DM. Her first PCNL was unsuccessful because of access failure. In this patient, homodynamic instability occurred several minutes after anesthesia and we could not continue the procedure. The demographic data and surgical outcomes in 3 subdivided groups, based on their BMI, are mentioned in Table 3. There was no statistically significant difference in each subdivided group between the prone and the supine position, except the higher stone-free rate in BMI < 25 group in the prone position.

DISCUSSION

Developments in instrumentation, radiologic imaging, and skill have certainly helped PCNL to attain new frontiers in terms of safety and efficacy [7]. PCNL is generally performed in a patient in the prone position [8], but there are some reports about PCNL performance in flank, modified supine, and complete supine positions, or with the help of other modifications, such as antigrade access, are reported [4,9,10,11,12,13,14,15].

Stone-free rate

Some authors compared PCNL in supine versus prone. The reported stone-free rate was between 88.7 to 89% in the supine position versus 84 to 91.6% in the prone position. Their stone-free rate was higher than others. They mentioned that it might be related to excluding complete staghorn stones, stones requiring multiple percutaneous renal access, and renal anomalies [2,9]. In our study, the stone-free rate was 78 and 73.3% in the prone and the supine positions, respectively, with no significant differences. In this study, we have evaluated the outcomes of PCNL on the basis of BMI. We haven‘t compared the effect of BMI on 1 solitary method of the operation. If there were a rise in the number of patients, the reliability of the statistical analysis would be more valid. Also in this study, there was not any statistically significant difference in stone-free rates between the prone and the supine groups in the patients with a BMI > 30. So, BMI was not an effective parameter in stone-free rates in PCNL. In other studies that compared the effect of BMI in prone PCNL, stone-free rates were similar in patients with different BMIs [16,17,18,19]. The patients with more than a 5 mm residual stone were scheduled for ESWL or second-look PCNL.

Fever

The frequency of fever after PCNL was reported 13.6 to 25.8% [3,20]. Sergeyev et al. evaluated the outcomes of PCNL according to BMI and kidney stone size and mentioned that the outcomes of PCNL seemed to be independent of patient BMI with regard to postoperative fever [21]. In our present study, the incidence of postoperative fever was higher in the prone group. In patients with a BMI > 30, 1 patient in the prone and 2 patients in the supine position experienced postoperative fever. In our study, all patients received appropriate antibiotics before PCNL. A lower frequency of fever in the supine position (which is a normal position) may be due to a lower rate of atelectasia and other pulmonary complications related to anesthesia in this situation. A shorter duration of anesthesia in the supine procedure may be an important factor, too. Also in our study, the rate of postoperative fever was not statistically different in the 3 BMI groups. The number of patients in this study was limited to a definite conclusion.

Bleeding needing transfusion

Shoma et al. reported that the incidence of acute bleeding was higher in the supine position (9 versus 5% of prone cases) [2]. Bleeding needing transfusion was one of our complications, seen in 8 and 15% of patients in the prone and supine positions, respectively (p = 0.25). Some patients had a lower Hb level before the procedure. If the Hb dropped to lower than 10 gr/dl, transfusion was done on the basis of our educational center policy. This could be the cause of a higher transfusion rate in our cases. Since the difference was not significant, it seems that BMI was not an effective factor in transfusions between the prone and the supine position in obese and morbidly obese patients.

Anesthesia time

A shorter operative time was one of the advantages of supine PCNL, which was mentioned in many studies [4,7,9]. Some studies reported the procedure time in the supine position as 45 to 300 min [3,4,7]. In our study, similar to other studies, the mean anesthesia time was 96.80 ± 29.66 minutes in the prone position versus 79.38 ± 38.38 minutes in the supine position, with a statistically significant difference (p = 0.01). This could be due to time lost in turning the patient at the beginning and end of the procedure in prone PCNL (repositioning of the patient). The other factor considered is the cost of operation time, which would affirm the supine approach in this regard. Also in the BMI 25 to 30 kg/m2 group, anesthesia time was shorter in the supine position than in the prone position (p < 0.0001). In groups with a higher BMI, anesthesia time was increased. The important factors in increasing anesthesia and procedural time in the patient with a higher BMI may be more difficult in intubation, resulting in a longer time to access the kidney, displacement of the Amplatz sheath during the procedure, and time wasted to correct its location. Other studies did not show any differences [16,17,19].

Hospital stay

Some studies have reported the mean hospital stay between 2 and 5.4 days for the supine and prone positions [2,3,7,9]. In our study, there was no statistically significant difference between the prone and the supine position in hospital stay (54.06 ± 14.34 hours in the prone versus 58.33 ± 13.80 hours in the supine position; p = 0.115). So, it seems that hospital stay was similar in prone and supine PCNL. Moreover, hospital stay in the 3 BMI groups was not significantly different in the prone and the supine position. In some studies that compared the outcome of PCNL in the prone position based on BMI, the hospital stay was similar [17,18,19]. But Sergeyev et al. showed that patients with a BMI < 25 kg/m2 revealed a significantly longer hospital stay (p = 0.01). They explained that the duration of the hospitalizations of these 2 patients affected the mean hospital stay (1 patient experienced a pulmonary embolism and the other, because of a very large staghorn calculus, underwent sandwich therapy) [21].

Tubeless PCNL

We showed that tubeless PCNL can be safe and effective [22]. Tubeless PCNL was done in 39 (78%) patients in the prone and 52 (86.7%) patients in the supine group (Table 2; Table 3). An external ureteral stent was inserted for a limited time in all patients. Tubeless PCNL for our patients was performed routinely and it may show that tubeless PCNL could be a safe and effective procedure. BMI was not an effective factor to perform nephrostomy in both the prone and the supine positions.

History of open surgery

Some reports mentioned that a history of open nephrolithotomy does not adversely affect the efficacy or morbidity of PCNL [23,24,25]. In contrast, other studies showed higher failure rates of PCNL in patients with prior open renal surgery [26]. In this study, 30 patients had a history of renal surgery (12 [24%] in the prone position versus 18 [30%] in the supine position). Major complications were not seen in any patients with a history of renal surgery, even in obese and morbidly obese patients. It seems that PCNL in both the prone and the supine positions was safe in patients with a history of renal surgery, regardless of BMI.

Effect of BMI in PCNL outcomes

Obesity and morbid obesity confer an increased risk of morbidity because of their association with diabetes and cardiovascular and respiratory disease [17]. It is clear that obesity plays a role in various methods of stone treatment [21]. Shockwave lithotripsy (SWL) is not usually efficient in treating upper urinary tract stones in obese patients due to several limitations [16,27]. There are many studies that evaluate the safety and outcomes of PCNL in the prone position in obese patients [16,17,18,19,21]. Bagrodia et al. evaluated the impact of BMI on clinical outcomes and the associated costs with PCNL. They found no significant differences among groups with regard to stone-free rate and complication rate, operative time, length of hospital stay, or need for multiple accesses [18]. In the same way, Pearle et al., El Assmy et al., and Koo et al. found insignificant differences in the outcomes or morbidity between obese and nonobese patients. The outcome of PCNL in their study was independent on patient BMI [16,17,19]. When compared with other positions, csPCNL offers the potential advantages of less patient handling, only draping the patient once, and easier access to the urethra. If PCNL is performed initially with spinal or regional anesthesia and general anesthesia is needed, the change is easier in this position. The supine position allows better airway management and may be less hazardous, especially for patients with compromised cardiopulmonary function, morbid obesity, or those who require a prolonged procedure. Access to upper calyces in this method is easier than the prone position. There is better drainage with the Amplatz sheath, and stone fragment evacuation is facilitated. If required, a more familiar approach for simultaneous ureteroscopic access is readily obtained, allowing combined percutaneous nephrolithotomy and ureteroscopy for the management of complex stone disease. In csPCNL, the puncture site for access is the posterior axillary line, which is far from the fluoroscopy tube [28]. De la Rosette et al. reported prone PCNL for obese patients, and staghorn calculi appear to be associated with decreased operative time, with similar bleeding rates and slightly better stone-free rates than supine PCNL [29]. In the present study, we have compared the outcome of PCNL in the prone and the supine positions in different BMI groups. There was no statistically significant difference in stone-free rates, anesthesia time, hospital stay, and transfusion rates between these 2 groups. It seems that supine PCNL is a safe and effective procedure in obese patients.

CONCLUSION

This study is a preliminary one to determine outcomes of prone and complete supine PCNL according to BMI, and more studies are needed to confirm it. Although the anesthesia time was increased in higher BMI groups, outcomes of PCNL in both the prone and the supine position were independent on patient BMI. This study showed that the prone and the supine PCNL in obese and morbidly obese patients were safe and effective. Although the gradients of pleural and transpulmonary pressures are reduced in the prone position, ventilation is distributed more evenly, and the dorsal chest wall becomes more compliant, favoring re-expansion of dependent lung regions [30,31,32], but the prone position has numerous disadvantages.

Although supine PCNL has numerous advantages and is routinely performed in some surgical centers throughout the world, its popularity is still minimal in the field of urology as a whole. Lifestyle changes require more time because urologists are familiar with prone PCNL. This general lack of acceptance most likely seems to be from the fear of colon injury during this procedure and a lack of training in educational centers.

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