Urodynamic characteristics of the modified orthotopic ileal neobladder Urodinamske karakteristike modifikovane ortotopne ilealne neobešike

Background/Aim. Radical cystectomy is the method of choice in management of muscle invasive, organ-confined tumors of the bladder (Т2-Т4, N0-Nx). The most frequent continent orthotopic urinary diversion after radical cystectomy is the ileal neobladder. A modified technique consists of using a shorter segment of the terminal ileum than the standard technique, around 30 cm. The aim of this study was to determine the urodynamic characteristics of the orthotopic ileal neobladder created by a modified technique. Methods. In this prospective clinical study we analyzed the urodynamic parameters of 24 patients who had underwent radical cystectomy with orthotopic urinary diversion by ileal neobladder created using a modified technique. In all the patients we performed invasive and noninvasive urodynamic investigations 12 months after the operation. The urethral pressure profile parameters analyzed were maximal urethral pressure, maximal urethral closure pressure and the functional urethral profile length. Results. The average age of the patients was 63 (49–73) years, 90% were males and 10% were females. The median length of the shorter segment of the terminal ileum was 28 (range 22–35) cm. Prior to enterocystometry and uroflowmetry postvoid residual (PVR) urine was measured by a urethral catheter. The median PVR was 16.7 (0–140) mL. The median enterocystometric capacity was 396 (range 372–532) mL. The median end filling pouch pressure was 27.6 (range 20–70) cmH20. The median maximal flow of urine was 22.1 (range 9.7– 39.5) mL/s and the average flow of urine was 9.61 (range 3.6–17.6) mL/s. Flow time in the analyzed group was 47.5 (range 22–119) s. The median maximal urethral pressure was 54 (range 12–101) cmH2O, maximal urethral closure pressure 36.6 (range 6–91) cmH2O. Functional urethral profile length was 14.9 (range 4–37) mm. Conclusion. An ileal orthotopic pouch created by a modified technique using a shorter segment of the terminal ileum after 12 months presents with urodynamic characteristics similar to the native bladder.

10% were females.The median length of the shorter segment of the terminal ileum was 28 (range 22-35) cm.Prior to enterocystometry and uroflowmetry postvoid residual (PVR) urine was measured by a urethral catheter.The median PVR was 16.7 (0-140) mL.The median enterocystometric capacity was 396 (range 372-532) mL.The median end filling pouch pressure was 27.6 (range 20-70) cmH 2 0. The median maximal flow of urine was 22.1 (range 9.7-39.5)mL/s and the average flow of urine was 9.61 (range 3.6-17.6)mL/s.Flow time in the analyzed group was 47.5 (range 22-119) s.The median maximal urethral pressure was 54 (range 12-101) cmH 2 O, maximal urethral closure pressure 36.6 (range 6-91) cmH 2 O. Functional urethral profile length was 14.9 (range 4-37) mm.Conclusion.An ileal orthotopic pouch created by a modified technique using a shorter segment of the terminal ileum after 12 months presents with urodynamic characteristics similar to the native bladder.

Introduction
Radical cystectomy is the method of choice in management of muscle invasive, organ-confined tumors of the bladder (Т2-Т4, N0-Nx) 1 .Radical cystectomy demands urinary diversion.Continent urinary diversion consists of creating a urinary reservoir that will enable urinary continence and voiding.They can be heterotopic (continent cutaneous urinary diversion) and orthotopic (pouch, neobladder) 2,3 .The modified technique consists of using a segment of the ileum around 30 cm in length, shorter than standard technique [3][4][5][6][7] .
Urodynamic investigations are functional and diagnostic procedures that are used to evaluate the function of the lower urinary tract.The orthotopic ileal neobladder "imitates" the native bladder and the same functional and diagnostic procedures can be used to evaluate the ileal neobladder 8 .

Methods
The prospective clinical study included 24 patients who underwent radical cystectomy with orthotopic ileal neobladder urinary diversion.In all the patients we performed invasive and noninvasive urodynamic investigations 12 months following the operation.Uroflowmetry was used as a noninvasive urodynamic procedure.Enterocystometry, urethral pressure profile (UPP) and measurement of postvoid residual (PVR) urine by catheter are invasive urodynamic procedures that were used.The urodynamic investigations were performed using the Medtronic Duet Encompass (Medtronic, Minneapolis, USA).Enterocystometry was performed using a cystometric transurethral filling catheter CH 8 by which the intraluminal pressure was measured during filling of the neobladder, a catheter for measurement of intraabdominal pressure CH 12, sterile NaCl 0.9% solution and transducers for intravesical and intraabdominal pressure were used.UPP was performed using a transurethral filling catheter CH 8, pullera -a device that pulls the catheter in a constant speed of 2 mm/s, and tranducers for intravesical pressure and urethral pressure profile.The change of pressure in the catheters are transferred to the transducer, that converts it into an electric signal and after that computer analyzes and presents the graphic and numeric results of measurements.
We determined the following urodynamic parameters: enterocystometric capacity of the neobladder, maximal neobladder pressure (pressure at enterocystometric capacity), the average flow rate, maximal flow rate, flow time, maximal urethral pressure, maximal uretharal closure pressure, functional length of the urethra and PVR.
All procedures were performed in accordance with the principles of sterility.The patients were informed in detail about the examination and they signed the consent form.The procedures were conducted in a standardized manner with the patient in a sitting position.In invasive urodynamic procedures antibiotic prophylaxis was conducted (ciprofloxacin 500 mg, one hour prior to the examination).The examinations were performed in accordance with the guidelines and terminology of the International Continence Society (ICS) 9 .

Results
In the monitored group of patients who underwent radical cystectomy because of muscle-invasive bladder cancer, urinary diversion was performed by orthotopic neobladder created using a shorter segment of the terminal ileum in the average length of 28 (22-35) cm.The demographic data, and results of invasive and noninvasive urodynamic investigations are presented in Table 1.The results of UPP are presented in Table 2.  Functional length of the urethra (mm) 14.9 (4-37)

Discussion
The role of a neobladder is to replace the bladder both in place and function.A neobladder that imitates the native bladder should have satisfying capacity, low intraluminal pressure and to enable physiological voiding frequency and urinary continence.Searching through the Medline and Pubmed database and professional literature up to December 2010, there are nine published papers which consider neobladders created of an ileal segment shorter than by the standard technique 4-7, 10- 14 .There are 7 papers that have been published which evaluated urodynamic characteristics of neobladders created by modified technique [4][5][6][7][10][11][12][13][14] .
Based on the available published data for neobladders created by the standard technique there are no standard values for urodynamic parameters.Although the data obtained by urodynamic investigations are objective, precise and comparable, this evaluation is not standard procedure in a follow-up period after radical cystectomy.There is limited number of published papers that consider urodynamic evaluation of neobladders compared to the large number of variations of ileal orthotopic neobladders (49 papers).
The length of the segment of terminal ileum is limited with the possibilities of creating the pedicle, so the average length of the segment was 28 cm in our patient group.Two studies analyzed neobladder created from 40 cm of the terminal ileum, while Constantinides et al. 5 used 36 cm of the terminal ileum 4,6 .In our previously published study we presented the use of a shorter segment of ileum than in other published papers and in this study as an upgrade of the previous one we evaluated the urodynamic characteristics of the neobladder created by a modified technique 7 .
In our study PVR was 16.7 mL (0-140), compared to 40 (0-150) mL and 30 mL presented in two other studies 4,5 .The median maximal flow rate in our group was 22.1 mL/s (9.7-39.5)and in Sevin´s 4 study 17.5 mL/s (11-30) 4 .The difference is significant and expected.It is a known fact that the neobladder enlarges in volume in the first year following the operation up to four times so will the capacity of the neobladder in our study 15 .This occurs only if they are frequently filled otherwise neobladder volume decreases in time if they are nonfunctional.The enlargement of the neobladder leads to creating a larger contact and resorptive surface of the neobladder that may cause an increase in metabolic and electrolyte abnormalities and may also lead to problems in voiding and an increase in PVR.Beside neobladder capacity many factors can have an influence on maximal flow rate: strength of the abdominal wall, position and shape of the neobladder, sphincteric mechanisam, possible stenosis of entero-urethral anastomosis and voiding position of the patient.Using a shorter segment of the terminal ileum decreases the capacity of the neobladder that leads to a smaller PVR 7 .
Enterocystometry is an invasive urodynamic procedure by which the pressure/volume relationship of the intestinal reservoir is measured.The prerequisite for creating a neobladder is intestinal detubularization 3 .Intestinal detubularization is needed to avoid the peristaltic activity of the small bowel and also by folding the bowel the circumference is doubled, thus doubling the volume 3 .Intestinal detubularization not only decreases intraluminal presssure, but also by change of shape changes the capacity and pressure on the wall of the small bowel.The clinical significance of Laplace´s law is that by creating a spheric reservoir of an intestinal segment we achieve that the capacity of the reser-voir increases by r² (r -radius of the bowel).By increasing the radius of the reservoir the intraluminal pressure decreases.Increasing the intraluminal pressure increases the pressure on the wall of the reservoir and with a larger capacity the influence of peristaltic activity on the increase of intraluminal presure decreases.There are some difficulties in conducting the examination and interpretation of the results of enterocystometry.First of all, this relates to the sensitivity of the neobladder as a subjective part of the examination and also to determine the enterocystometric capacity of the neobladder.Compared to the native bladder to determine the sensitivity of the neobladder is very difficult because patients have impaired feeling for the need to void but instead feel pressure in the place of the neobladder.Enterocystometric capacity is determined by a strong desire to void or when it is absent with onset of leakage beside the cystometric catheter 16 .In our study the average enterocystometric capacity was lower compared to the Sevin group where it was 550 (310-720) mL 4 .Enterocystometric pressures at enterocystometric capacity are approximately the same and comparable to the Sevin group 26.4 (11-48) cmH 2 0 4 .We can conclude that the capacity of the neobladder created by modified technique in our group is similar to the native bladder with an unsignificant difference in pressure at enterocystometric capacity.
The measurement of the UPP is not only to determine if the patient is continent or the level of incontinence, but to understand the mechanism of urethral closure and appropriate urodynamic parameters 16 .In our group we considered the average maximal urethral pressure and maximal urethral closure pressure.In the study of Kakizaki et al. 14 the average maximal urethral closure pressure was 49.9 cmH 2 0. The patient is continent till the moment when the maximal urethral closure pressure exceeds the intraluminal pressure of the native bladder or the neobladder 8 .The values of the maximal urethral closure pressure and maximal urethral pressure can have influence on nocturnal continence especially if the maximal urethral closure pressure is < 45cmH 2 O 17 .In our study the maximal urethral closure pressure is lower than in the Kakizaki study and can have influence on continence (day and night) but that cannot be analyzed isolated from other urodynamic parameters (enterocystometric pressure, capacity and PVR).

Conclusion
Analyzing the urodynamic parameters of invasive and noninvasive urodynamic procedures we can conclude that the neobladder created by the modified technique using a shorter segment of the terminal ileum compared to the standard neobladder has functional characteristics similar to the native bladder.Adequate capacity, small PVR, good maximal flow rate, low enterocystometric pressure and satisfying UPP decreases the possibility of functional and metabolic abnormalities of the upper urinary tract and can influence quality of life.Prospective studies with larger numbers of patients included and a longer follow-up period are needed to determine all advantages of the modified technique over the standard technique.