This web only provides the extract of this article. If you want to read the figures and tables, please reference the PDF full text on Blackwell Synergy. Thank you.

- Clinical Experience -

Pressure-flow studies in patients with benign prostatic hyperplasia: a study comparing suprapubic and transurethral methods

Shan-Chao Zhao, Shao-Bin Zheng, Wan-Long Tan, Peng Zhang, Huan Qi

Department of Urology, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China

Abstract

Aim: To compare the use of the suprapubic puncture method versus the transurethral method in pressure-flow studies in patients with benign prostatic hyperplasia.  Methods: Twenty-three men with benign prostatic hyperplasia underwent both suprapubic and transurethral pressure-flow studies during a single session. Standard pressure-flow variables were recorded in all patients with both methods, enabling calculation of obstruction using commonly used grading systems, such as the urethral resistance algorithm, the Abrams-Griffith (AG) number and the Schäfer linear nomogram.  Results: There were statistically significant differences between the methods in the mean values of maximum flow rate (P < 0.05), detrusor pressure at the maximum flow (P < 0.01), urethral resistance algorithm (P < 0.01), AG number (P < 0.01) and maximum cystic capacity (P < 0.01). Of the men in the study, 10 (43.5%) remained in the same Schäfer class with both methods and 18 (78.3%) in the same AG number area. Using the transurethral method, 12 (52.2%) men increased their Schäfer class by one and 1 (4.3%) by two. There were also differences between the suprapubic and transurethral methods using the AG number: 4 (17.4%) men moved from a classification of equivocal to obstructed and 1 (4.3%) from unobstructed to equivocal.  Conclusion: The differences between the techniques for measuring intravesical pressure alter the grading of obstruction determined by several of the commonly used classifications. An 8 F transurethral catheter significantly increases the likelihood of a diagnosis of bladder outlet obstruction when compared with the suprapubic method. (Asian J Androl 2006 Nov; 8: 731_735)

Keywords:urodynamics; pressure-flow study; suprapubic; transurethral; benign prostatic hyperplasia; bladder outlet obstruction

Correspondence to: Dr Shao-Bin Zheng, Department of Urology, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China.

Tel: +86-20-6164-1761, Fax: +86-20-6164-1763
Email: urocyber@21cn.com
Received 2005-12-02 Accepted 2006-06-16

DOI: 10.1111/j.1745-7262.2006.00204.x

1 Introduction

Benign prostatic hyperplasia (BPH) is a common disease in elderly men. Delineation of the essence of BPH is debated. The use of diagnostic testing in the evaluation of suspected outlet obstruction and in the prediction of the success of treatment is controversial. Studies show that approximately 20_30% men with BPH are not obstructed and that 50_80% have detrusor instability [1, 2]. Symptoms, prostate size, free uroflowmetry parame-ters and the amount of post-void residual urine are associated with obstructive voiding but the correlation with the grade of obstruction is weak [3, 4]. Urodynamic study with pressure-flow analysis is considered the gold standard to quantify the degree of bladder outlet obstruction (BOO) [3].

During pressure-flow studies intravesical pressure can be measured using either transurethral or suprapubic lines. The transurethral method is generally used, but the suprapubic route has the theoretical advantage of leaving the urethra untouched during the measurements and, therefore, might preclude any artifacts produced by instrumentation [5].

The purpose of the present study is to compare the two urodynamic methods of measuring intravesical pressure in a group of men undergoing investigation for BPH, and to identify which urodynamic variables are affected by the presence of an 8 F urethral catheter during the voiding phase and, consequently, whether there are any changes in the grading of BOO using the commonly reco-gnized grading systems.

2 Patients and methods

2.1 Patients

Pressure-flow studies were performed on 23 men (mean age 69.3 years, range 57_77 years) attending our unit for the assessment of BPH. All men had prostatic enlargement on clinical examination but normal levels of prostate specific antigen. The results of urine analysis were negative before investigation. Both suprapubic and transurethral measurements were undertaken on all patients in a single session. Each patient was asked to ensure that he had a full bladder he they attended. On arrival, patients were randomized to receive either the suprapubic procedure or the transurethral procedure, or vice versa. Before every examination, the examiners explained the process to patients and obtained their informed consent to participate in the study.

2.2 Transurethral method

An 8 F double-lumen pressure catheter was introduced into the bladder transurethrally under sterile conditions and a 6 F single-lumen pressure catheter was introduced into the rectum. Fluid-filled lines with external pressure transducers and Dantec Menuet equipment (Dantec, Copen-hagen, Danmark) were used. The bladder was filled with saline at 20ºC (40 mL/min) and all pressure-flow studies were performed with the patient standing. The required variables were recorded simultaneously and the electronic calculations were subsequently carried out.

2.3 Suprapubic method

The bladder was filled with saline (approximately 300_400 mL) until the patient felt abdominal distention and wanted to urinate. The midline was then infiltrated with local anesthetic (1% plain lignocaine). A 14 F puncture needle was inserted into the bladder and a 14 F double-lumen catheter was passed through the needle and then the needle was withdrawn over the line. A three-way tube was used to connect the 14 F catheter, the bladder piezometer tube and the delivery tube. A 6 F single-lumen pressure catheter was also introduced into the rectum. Following the introduction of the suprapubic line, the patient voided and the suprapubic pressure-flow variables were recorded.

2.4 Variables choices and diagnosis standards of bladder outlet obstruction

Maximum flow rate (Q_max), detrusor pressure at maximum flow (Pdet, Q_max) and maximum cystic capacity (MCC) were recorded manually from the pressure-flow tracing. The urethral resistance algorithm (URA), Abrams-Griffiths number (AG) and Schäfer linear nomogram were calculated. The diagnosis standards of BOO were formulated according to the standardization of the International Continence Society [6, 7].

2.5 Data processing

The paired t-test was used to determine the level of statistical significance for any difference between methods, with P < 0.05 assumed to indicate significance.

3 Results

There were no complications during the study. The pressure-flow data from the recordings are shown in Table 1. There were significant differences between the mean values of the two methods for Q_max, Pdet, Q_max, MCC, URA and AG number.

The percentage of patients in each class of the two nomograms is given in Table 2. Of men in the study, 10 (43.5%) remained in the same Schäfer class with both methods and 18 (78.3%) in the same AG number area. Using the transurethral method, 12 (52.2%) men increased their Schäfer class by one and 1 (4.3%) by two. There were also differences between the suprapubic and transurethral methods using the AG number: 4 (17.4%) men moved from a classification of equivocal to obstructed and 1 (4.3%) from unobstructed to equivocal. Therefore, 5 (21.7%) men moved from one area of the nomogram to a more obstructive region (Figure 1).

4 Discussion

The precise identification of patients with BOO as a result of BPH has become relatively more important. Pressure-flow studies are the only urodynamic tests that allow differentiation between a Q_max secondary to obstruction and an impaired Q_max secondary to suboptimal detrusor function [8]. Indeed, pressure-flow analysis has been generally accepted as the gold standard in measuring outcome and certainly in quantifying the grade of BOO [3, 5], and it has been verified significant for both diagnosis before surgical treatment and evaluation after operation, such as before and after transurethral resection of prostate [9, 10]. Therefore, it is very important to get precise results from the examination. Pressure-flow studies are invasive, requiring the insertion of recording devices into the bladder and into the rectum. The results obtained should be precise as far as possible to offset patient discomfort and cost [8]. Currently, the transurethral route is used most widely for the simultaneous recording of pressure and flow during voiding. However, there is the theoretical possibility that a urethral pressure line could interfere with pressure and flow recording from the urethra and bladder. An alternative technique is to use a suprapubic catheter. Clearly, such a technique would avoid any influences of urethral instrumentation and cathete-rization on detrusor pressure and flow rate, although it would obviously make the investigation of pressure-flow studies more invasive [11].

Does the transurethral catheter significantly influence the recording of measurements? Which method should we choose? There have been few formal studies on either method and the opinions are discordant. Klingler et al. [12] noted an increase in obstruction grade when transurethral pressure-flow studies are performed with larger tubes within the urethra. Von Garrelts [13] reported that catheters with an outer diameter of 1.1_5.0 mm impeded flow but did not affect voiding pressures. Smith [14] found that the use of a urethral catheter (size not stated) compared with a suprapubic catheter and produced a small increase in voiding pressure in a normal 33-year- old man. In a group of boys 3_15 years old, Griffiths and Scholtmeijer [15, 16] found that the combination of a 8 Ch. and 3.5 Ch. catheter had a more obstructive effect than a 3.5 Ch. catheter alone, whereas in only 3.5% of 111 young girls 4_15 years old did an 8 Ch. catheter had an obstructive effect. Neal et al. [17] studied the effect of a large (combined 4 and 10 Ch. catheters) versus a small (1.1 mm diameter epidural line) catheter assembly on detrusor pressure and flow in 20 men before prostatectomy and 10 men after prostatectomy. They found that detrusor pressure at maximum flow was significantly greater and the maximum flow rate was significantly smaller in the large catheter study than in the small catheter study, suggesting that this probably occurred because the larger catheter caused obstruction. Yalla et al. [18] measured voiding pressures in 10 men and found no significant change when comparing a 10 with a 5 F catheter. Zhang et al. [19] concluded that a 7 F urethral catheter appears to have a significant impact on maximum flow rate through studying 44 men with lower urinary tract symptoms. Trumbeckas et al. [20] also confirmed that a catheter of 7 F slightly diminishes maximum flow rate.

Recent studies investigate how to choose the techniques in pressure-flow studies. Madsen et al. [8] divided 25 patients into transurethral groups (4 F catheter was used) and suprapubic groups. Although the studies showed that the reproducibility of the test did not depend on whether the intravesical pressure is measured by transurethral catheterization or suprapubic puncture, they suggest that there is a physiologic difference between the two tests. Similar to the present study, in the study by Walker et al. [5] standard pressure-flow variables were measured in 35 patients using both methods. The study by Walker et al. [5] demonstrates that there are differences in the classification of obstruction between the suprapubic and transurethral (10 F catheter was used) routes, and that the transurethral method tends to indicate greater obstruction.

In the present study, there were significant differences in both the recorded variables and the grade of obstruction

between the suprapubic and transurethral (using an 8 F urethral catheter) methods. The artificial obstruction increases the urethral resistance with urethral stricture and interrupts urination. This influences not only maximum flow rate and detrusor pressure but also maximum cystic capacity, because the urethral catheter's stimulation potentizes the patient's micturition desire and shortens the time to their urgent desire. This probably affects the results for both diagnosis before surgical treatment and evaluation after operation, such as before and after transurethral resection of prostate.

In conclusion, the differences between the methods for measuring intravesical pressure alter the grading of obstruction determined by several of the commonly used classifications. An 8 F transurethral catheter does significantly increase the likelihood of a diagnosis of BOO when compared with the suprapubic method. We advocated the suprapubic method because of its precision. If the transurethral method is used, we suggest a catheter smaller than 8 F is needed. Whichever method chosen, the examiners should make the patients understand the process and obtain their consents.

References

1 McGuire EJ. The role of urodynamic investigation in the assessment of benign prostatic hypertrophy. J Urol 1992; 148: 1133_6.

2 Wu ZJ, Gao JZ, Wu KR, Guan DL, Wang B. The role of pressure-flow studies in operative indication for BPH. Chin J Urol 1998; 19: 285_7.

3 Liao LM, Shi BY, Liang CQ, Schäfer W. Evaluation for Madigan's prostatectomy in patients with benign prostatic hyperplasia. Asian J Androl 2001; 3: 33_7.

4 Rosier PF, de la Rosette JJ, Koldewijn EL, Debruyne FM, Wijkstra H. Variability of pressure-flow analysis parameters in repeated cystometry in patients with benign prostatic hyperplasia. J Urol 1995; 153: 1520_5.

5 Walker RM, Di Pasquale B, Hubregtse M, Hubregtse M, St Clair Carter S. Pressure-flow studies in the diagnosis of bladder outlet obstruction: a study comparing suprapubic and transurethral techniques. Br J Urol 1997; 79: 693_7.

6 Griffiths D, Hofner K, van Mastrigt R, Rollema HJ, Spangberg A, Gleason D. Standardization of terminology of lower urinary tract function: pressure-flow studies of voiding, urethral resistance, and urethral obstruction. International Continence Society Subcommittee on Standardization of Terminology of Pressure-Flow Studies. Neurourol Urodyn 1997; 16: 1_18.

7 van Mastrigt R, Griffiths DJ. ICS standard for digital exchange of urodynamic study data. Neurourol Urodyn 2004; 23: 280_1.

8 Madsen FA, Rhodes PR, Bruskewitz RC. Reproducibility of pressure-flow variables in patients with symptomatic benign prostatic hyperplasia. Urology 1995; 46: 816_20.

9 Homma Y. Pressure-flow studies in benign prostatic hyperplasia: to do or not to do for the patient? BJU Int 2001; 87: 19_23.

10 Roehrborn CG, Burkhard FC, Bruskewitz RC, Issa MM, Perez-Marrero R, Naslund MJ, et al. The effects of transurethral needle ablation and resection of the prostate on pressure flow urodynamic parameters: analysis of the United States randomized study. J Urol 1999; 162: 92_7.

11 Reynard JM, Lim C, Swami S, Abrams P. The obstructive effect of a urethral catheter. J Urol 1996; 155: 901_3.

12 Klingler HC, Madersbacher S, Schmidbauer CP. Impact of different sized catheters on pressure-flow studies in patients with benign prostatic hyperplasia. Neurourol Urodyn 1996; 15: 473_81.

13 Von Garrelts B. Intravesical pressure and urinary flow during micturition in normal subjects. Acta Chir Scand Suppl 1957; 114: 49_66.

14 Smith JC. Urethral resistance to micturition. Br J Urol 1968; 40: 125_56.

15 Griffiths DJ, Scholtmeijer RJ. Precise urodynamic assessment of anatomic urethral obstruction in boys. Neurourol Urodyn 1982; 1: 97_100.

16 Griffiths DJ, Scholtmeijer RJ. Precise urodynamic assessment of metal and distal urethral stenosis in girls. Neurourol Urodynam 1982; 1: 89_95.

17 Neal DE, Rao CV, Styles RA, Ng T, Ramsden PD. Effects of catheter size on urodynamic measurements in men undergoing elective prostatectomy. Br J Urol 1987; 60: 64_8.

18 Yalla SV, Waters WB, Snyder H, Varady S, Blute R. Urodynamic localization of isolated bladder neck obstruction in men: studies with micturitional vesicourethral static pressure profile. J Urol 1981; 125: 677_84.

19 Zhang P, Wu ZJ, Gao JZ. Impact of intrta-urethral catheter on uroflow rate in pressure-flow study. Chin J Urol 2004; 25: 274_6.

20 Trumbeckas D, Milonas D, Jievaltas M, Danilevicius M, Matjosaitis AJ. Influence of catheter on urinary flow during urodynamic pressure-flow study in men with symptomatic benign prostatic hyperplasia. Medicina (Kaunas) 2006; 42: 15_21.