DIAGNOSIS AND GRADING OF OUTFLOW

OBSTRUCTION

Z. KHAN, M.D. M. MIEZA, M.D. A. BHOLA, M.D. P STARER, M.D.

From the Department of Urology, Beth Israel Medical Center, New York, New York

ABSTRACT-Urodynamic data from 66 male patients with obstruction due to benign prostatic hyperplasia were analyzed. Criteria for grading the severity of outflow obstruction based on uroflowmetry, post void residual urine, maximum bladder contraction (Pmax), and pressure during voiding (Pvoid) were developed. In selected cases, voiding cystourethrography also may be needed. These criteria help determine the need for prostatectomy. Unnecessary prostatectomies can then be avoided and can lead to significant reduction in mortality, morbidity, and health care expenses.

Urinary outflow obstruction is a problem in which the remedy, more often than not, is sur- gical. Based on an unclear set of diagnostic cri- teria, prostatectomy is recommended for many patients. These criteria include symptoms of “prostatism,” rectal examination of the pros- tate, cystoscopy, residual urine measurement, and bladder films taken as part of an intrave- nous pyelogram. Unfortunately these criteria are highly unreliable in diagnosing outflow ob- struction.’

The enormous number of transurethral pros- tatectomies (TURP) performed annually has been noted by health care policy makers. A re- cent report from the American Urological Asso- ciation has identified TURP procedures as a leading surgical expense for Medicare in the fis- cal year 1984. During 1984, Medicare financed 323,120 TURP procedures at an approximate total cost of $327,104,795.2 In addition to the expense, the morbidity and mortality after transurethral prostatectomy are also major con- cerns. Postoperative complications include in- continence and urethral stricture. In a recent report from the National Institutes of Health, the mortality after TURP has been documented

to be 1.1 per cent within the first thirty days, and 9.6 per cent within the first year.

The incidence of urethral stricture after pros- tatectomy has been reported to be 5.5 per cent. 3 Frequently, internal urethrotomy is needed to correct the stricture. The procedure has to be repeated in most cases. The cost of one internal urethrotomy including diagnosis and two days of hospitalization is approximately $2,000. The incidence of post prostatectomy urinary incon- tinence is estimated at 0.2 to 1.0 per cent.4s5 The cost of control of continence by conservative methods is $200-600 per patient per year. If in- continence was to be controlled by the newer method of artificial urinary sphincter each pro- cedure would cost $9,000. This tremendously adds to the national economic burden. For these reasons, unnecessary prostatectomies should be avoided.

Since accurate diagnostic criteria are not available, many TURPs are performed based solely on urinary symptoms. A significant pro- portion of such prostatectomies are perhaps un- necessary because there is no actual outflow ob- struction. Definite guidelines for the diagnosis of outflow obstruction are therefore needed.

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TABLE I. Criteria used to categorize outflow obstruction

Natural Residual Grade Uroflowmetry Urine Pmax Pvoid

Normal Normal Nil 80-100 15-25 Mild obstruction Normal Nil 80-100 35-45 Moderate obstruction Poor Nil 80-100 55-65 Severe obstruction Poor + 80-100 70 + High pressure/high flow

with obstruction Normal or poor f 135 + 55-70 + Low pressure/low flow

without obstruction Poor f 55 15-25

These could lead to a reduction of unnecessary prostatectomies and lower health care costs, operative mortality, and morbidity. We present our guidelines for the urodynamic diagnosis of outflow obstruction.

Material and Methods To define our criteria for the diagnosis and

grading of bladder outlet obstruction, we retro- spectively analyzed the data on 100 sympto- matic male patients, whom we had diagnosed as having an obstruction, based on urodynamic and radiologic studies, during the years 1983- 1985. Thirty-four of these patients were unable to void during the urodynamic test and were excluded from the study. Thus the group under study actually was comprised of 66 patients. Their ages ranged from forty-one to ninety- three years (average 68.3 years). The duration of symptoms in these patients ranged from one month to six years (average duration 2 years). We utilized a control group consisting of 23 symptomatic males, who had been found to be normal (no obstruction) on urodynamic and ra- diologic evaluations. This group of unob- structed patients had been tested during the same period (1983-1985) as the group with no obstruction, and their ages ranged from thirty- one to eighty-one years (average 66 years).

A detailed history and physical examination had been performed on patients in both groups. Physical examination included perineal sensa- tion, bulbocavernosus reflex, and digital ex- amination of the prostate. Following this, natu- ral uroflowmetry was performed using a DISA rotary uroflowmeter (Model 21-C-10). The vol- ume of urine voided, the peak flow rate, and the residual urine were measured. The peak flow rates were then analyzed against the vol- ume of urine voided, using nomograms devised by Siroky, Olsson, and Krane.e

Soon after voiding, a 14F Foley catheter was inserted, and the balloon of the catheter was in-

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flated. Slight traction was applied to the cathe- ter so that the balloon could occlude the blad- der neck, and no fluid would escape during measurement. Cystometric studies were per- formed using a uromanometer (DISA 21-C-15). The bladder was infused with isotonic saline at body temperature, at a rate of 100 cc/min with the patient in the supine position. When a strong desire to micturate was experienced, the patient was asked to void and the maximum de- trusor pressure (Pmax) was noted. The actual pressure rise due to bladder contraction was then calculated by subtracting the usual base- line pressure (lo-20 cm HeO) from the reading obtained on the manometer. If the patient failed to generate a contraction in the supine position, this procedure was performed in a sit- ting or standing position.

The Foley catheter was then replaced with a pediatric feeding tube (F8). The bladder was filled in the same manner as mentioned. When the bladder was full, the patient was asked to void around the catheter, and the voiding pres- sure (Pvoid) was measured during the free flow of urine. As in the measurement of Pmax, the actual pressure rise (Pvoid) was calculated by subtracting the usual baseline pressure from the reading obtained on the manometer. During measurement of Pvoid and Pmax, the proce- dure was repeated so that accurate reproduc- ible readings could be obtained.

We found Foley catheters to be useful in pa- tients who have high residual urine, since the pediatric feeding tube requires a long time to empty the bladder in these cases. The patients then underwent voiding cystourethrogram, and signs of obstruction were noted.

Results

The analysis of data from 23 unobstructed and 66 obstructed patients helped us to develop the criteria used in this report (Table I).

73

FIGURE 1. Range of bladder pressure in normal mictutition.

Mild Moderate Severe

FIGURE 2. Range of voiding pressure in various de- grees of outjlow obstruction.

Unobstructed (high flow rate)

Obstructed (Normal flow rote)

FIGURE 3. Elevated Pmax in high-pressure bladder causing high flow rates in unobstructed patients and normal flow rates in severely obstructed patients.

In our group of unobstructed patients, the voiding pressures (Pvoid) ranged from 9 to 29 cm He0 (average voiding pressure, 22 cm HzO), while the maximum bladder pressure (Pmax) ranged from 60 to 130 cm Hz0 (average Pmax, 80 cm H,O). Based on this sample, we established our range of normal Pvoid as 15-25 cm HzO, and Pmax as 80-100 cm Hz0 (Fig. 1).

During analysis of the 66 obstructed patients, the results of uroflowmetry were correlated with the Pvoid and Pmax of these patients. In evaluating the degree of obstruction, the pres- ence or absence of residual urine (more than 100 mL), was taken into account. We found that 11 patients had mild obstruction, 12 had moderate obstruction, and 18 had severe ob- struction. The measurement of Pmax helped us in categorizing the bladder into normal, low- pressure, and high-pressure types. In our pa- tients with mild obstruction the Pvoid ranged from 29 to 48 cm He0 (average, 37 cm HzO) . In the moderately obstructed patients, the Pvoid ranged from 44 to 61 cm Hz0 (average, 52 cm HSO). In the severely obstructed patients, the Pvoid ranged from 65 to 158 cm He0 (average, 94 cm HSO) (Fig. 2).

Of 66 patients, it was found that 22 had a Pmax above 120 cm HzO. Hence, these patients

Unobstructed Low Flow Rates (low flow rate) (residual urine)

FIGURE 4. Low-pressure bladder causing low flow rates in obstructed and unobstructed patients.

were placed into another category of “high- pressure bladder” patients. The high bladder pressure compensated for the outflow obstruc- tion in these patients, therefore the flow rates did not appear to be severely affected. Hence, it is possible to underestimate the degree of out- flow obstruction, if only uroflowmetry is relied on. In this group the Pmax ranged from 123 to 266 cm He0 (average, 153 cm HzO), while the Pvoid ranged from 30 to 158 cm He0 (average, 86 cm HzO) (Fig. 3).

Below average intravesical pressures (low pressure with low flow rates) were generated in 7 patients, in whom the Pvoid ranged from 29 to 64 cm (average, 44 cm HzO), and the Pmax ranged from 34 to 68 cm Hz0 (average, 51 cm HSO). In this group of patients uroflowmetry values were disproportionately poor compared to the degree of obstruction. In some cases, the outflow obstruction was very mild, yet the uroflow rates were very low. In this group of patients when significant outflow obstruction develops, the uroflow rates further deteriorate

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and post void residual urine increases. This is out of proportion to the degree of obstruction. It is important to bear in mind that even after relief of obstruction by surgery, the uroflow rates cannot be expected to return to normal. In most cases even the residual urine may not de- crease significantly. Does this indicate surgical failure? This situation can be predicted pre- operatively by measuring the maximum detru- sor pressure (Fig. 4).

Comment

From a conceptual point of view, it is impor- tant to realize that an enlarged prostate and an obstructing prostate are two separate entities.’ Digital examination of prostatic size is known to correlate poorly with the degree of obstruc- tion.s An “enlarged” prostate does not necessar- ily mean an “obstructing” prostate. A prostate may enlarge considerably and yet not cause urethral obstruction. On the other hand, a slight enlargement of the prostate may com- press the urethra and cause urinary retention. It is the degree of obstruction which determines the necessity for surgery and not the size of the prostate.

It is difficult to determine the degree of ob- struction produced by the prostate gland. The size of the prostate on rectal examination does not give any information about the degree of obstruction it causes. Similarly cystourethros- copy is relatively uninformative regarding de- gree of obstruction except for the stress changes in the bladder. l Visual inspection of the prostate affords little information. The common obser- vation of “bulging lateral lobes, meeting in the midline,” does not correlate with outflow ob- struction. Although cystoscopy plays an impor- tant role in the diagnosis of other bladder con- ditions, notably bladder tumor or stone, it is valueless in the diagnosis of benign prostatic hy- perplasia (BPH). This practice is deeply rooted in tradition, and its role must be reevaluated. Similarly, it is difficult to predict obstruction based on determination of the residual urine.e Hypertrophic changes in the bladder are more reliable in reflecting the degree of outflow ob- struction. However, there are other entities which can produce similar changes in the blad- der, such as detrusor hyperreflexia.

The role of radiologic studies has been evalu- ated in the past. The intravenous urogram is not recommended as a routine diagnostic proce- dure in patients with BPH.‘O Bauer, Garrison,

and McRobertsll state that since positive results are infrequent, IVP is not indicated and is cer- tainly not cost-effective as a diagnostic test. In their opinion a saving of $75,909,996 can be made in annual health care costs by avoiding the unnecessary use of IVP preoperatively. In contrast, the voiding cystourethrogram pro- vides useful information regarding the nature of outflow obstruction.12 We rely on this radio- logic study to localize the site of obstruction in males younger than fifty with suspected out- flow obstruction, or in males in whom prostate surgery has failed to relieve the outflow ob- struction. Voiding cystourethrogram is also use- ful in patients with neurologic disorders. In fact, voiding cystourethrogram with simulta- neous pressure flow measurements is considered the method of choice in diagnosing obstruc- tion. l3

Recently abdominal and transrectal ultra- sound has been utilized more frequently in pa- tients with BPH. The size of the prostate now can be accurately measured, while prior to the development of sonography estimation of the size of the prostate had been very subjective. Postvoid residual urine, thickness of bladder wall, and state of upper urinary tract also can be judged by ultrasound. l4 But the degree of ob- struction cannot be measured.

With the great progress made during the past two decades in the science of urodynamics, this technology has been utilized to study patients with symptoms of outflow obstruction. It has been noted that many patients with symptoms of prostatism may not have outflow obstruction at all. In 1978, Abrams and Feneley15 in a study on 318 patients with suspected outflow obstruc- tion (based on symptoms alone) found that 33 per cent of patients actually had unobstructed micturition. These symptoms may be secondary to detrusor instability. Uroflowmetry is used frequently as a method to screen patients for outflow obstruction. The measurement of uroflowmetry became practical when Drake in 19481e and Von Garrelts in 1956l’ developed their uroflowmeters. This technique was con- sidered simple, noninvasive, and fairly ac- curate. Flow rates vary with the volume voided. This always must be taken into ac- count, especially when the volume voided is less than 150 mL. From his study on 117 patients with possible obstruction, Abrams’ concluded that only half of the cases could be objectively classified as obstructed or unobstructed from maximum flow rates alone.

UROLOGY I JULY 1988 I VOLUME XxX11, NUMBER 1 75

Smith,l in his work, had measured the urethral resistance by applying the formula R = P/F2. In his opinion it was accurate in the

majority of cases except in 1 patient. However, this concept has been criticized (International Continence Society, 198018). Abrams and Grif- fith in 1979u’ stated that in about two thirds of their cases obstruction could be assessed satis- factorily from the maximum flow rate together with the detrusor pressure at maximum flow rate. Yet they did not find the calculation of urethral resistance from these parameters help- ful. Their graphic representation of detrusor pressure against flow rate was considered useful in the remaining one third of their patients. However, this method of plotting a pressure- flow graph is even more laborious and would be difficult to perform routinely in a busy clinic. When significant outflow obstruction is present the flow rate decreases and voiding pressure in- creases. This change is proportional to the out- flow obstruction.

However, the uroflowmetry results can be deceiving. Since there can be an increase in the voiding pressure to compensate for outlet ob- struction, the urinary flow rate may not reflect the degree of obstruction. In a small number of cases the voiding pressure can be so high that it can result in almost normal uroflow rates in spite of significant outflow obstruction. There- fore, in order not to miss the diagnosis of out- flow obstruction, the urinary flow rate must be interpreted in relation to the voiding pressure.

Uroflowmetry also can be misleading in pa- tients with poor detrusor contraction. The poor detrusor contraction (underactive detrusor) will not generate sufficient pressure to drive urine through the urethra. Hence uroflow rates may be poor even in the absence of any outflow ob- struction. For this reason, it is important to measure the capability of the detrusor to de- velop maximum isometric contraction (Pmax). In our study, patients with Pmax of 55 cm H,O or less had seriously compromised detrusor con- traction. The detrusor underactivity may be a primary problem or may be secondary to long- standing outflow obstruction. The capacity of the bladder and the amount of residual urine may help in clinical differentiation.

There is a wide range of normal values for micturition pressure reported in the literature. In a small study consisting of 10 persons, Bauman in 195520 concluded that the mean voiding pressure in men was 60 cm Hz0 and in women 52 cm H20. Murphy and Schoenberg in

196021 reported the normal voiding pressure to be between 12 and 20 cm H20. A voiding pres- sure above 50 cm Hz0 was seen in obstructed children. Webster and Older in 198022 found that 37 per cent of their obstructed patients had voiding pressures within the normal range. However, they considered 60 cm Hz0 as the up- per limit of their normal range. The variation in normal voiding pressure is primarily due to difference in technique. Many factors, such as size of urethral catheter, position of the patient, and method of recording the pressure, play a significant role.

It is clear that a single criterion cannot be de- veloped to diagnose and grade outflow obstruc- tion. However, we believe that a great deal is known about the dynamics of micturition to de- velop guidelines for diagnosing and grading the outflow obstruction from the clinical point of view. In our experience, the following four measurements serve this purpose adequately: (1) uroflowmetry, (2) post void residual urine, (3) maximum bladder contraction (Pmax), (4) voiding pressure (Pvoid), (5) voiding cys- tourethrography (in selected cases).

Prostatectomy cannot be recommended on the basis that obstruction will become worse in future years, if not corrected. Ball, Feneley, and Abrams23 reviewed the five-year follow-up of 107 patients with prostatic symptoms who, on first presentation, were not considered clini- cally in need of prostatectomy. All of these pa- tients had urodynamic measurements to sup- port the diagnosis. Only 10 patients later required prostatectomy, 16 noted overall wors- ening of their symptoms, 31 noted improve- ment, and the remaining 50 had little or no change in symptoms. In addition, sequential urodynamic studies showed little changes in these patients.

How is the need for prostatectomy deter- mined? The mere presence of outflow obstruc- tion is not an indication for surgery. If the ob- struction causes significant symptoms to interrupt the daily routine of the patient, then surgery is indicated. The post surgical results will be rewarding. The common and frequent pitfall of diagnosis is to rely on symptoms alone, without confirmation that symptoms are being produced by outflow obstruction. The symp- toms produced by detrusor instability alone closely mimic those produced by obstruction. Patients who are found to have significant re- sidual urine and/or adverse effects on the upper tracts also will require surgery provided that

76 UROLOGY I JULY 1988 i VOLUME XxX11, NUMBER 1

significant outflow obstruction is the cause. However, patients with poor bladder contrac- tility due to prolonged obstruction (decompen- sated detrusor) can have unsatisfactory results after surgery. The alternate choice of clean in- termittent self-catheterization should be care- fully considered in such cases.

It is our opinion that by utilizing the afore- mentioned criteria the outflow obstruction can be accurately diagnosed and graded in terms of severity. Therefore, the surgeon can rule out other conditions mimicking prostatism and fre- quently resulting in disappointing outcome af- ter surgery. Because of this selection process, there is considerable national economic saving and reduction of mortality and distressing mor- bidity. This can only serve to raise confidence and trust in this surgical specialty.

First Avenue and 16th Street New York, New York 10003

(DR. KHAN)

References

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2. Reed JF Jr: OMB and HCFA at TURP clinical necessity pro- gram, Bull Am Urol Assoc 13: 2 (1987).

3. Habib NA, and Luck RJ: Results of transurethral resection of benign prostate, Br J Urol70: 218 (1983).

4. Alfthan 0: Treatment of post-prostatectomy incontinence, An Chir Gynaecol 71: 244 (1982).

5. Furlow WL: Post prostatectomy urinary incontinence. Etiology, prevention and selection of surgical treatment, Urol Clin North Am 5: 347 (1978).

6. Siroky MB, Olsson CA, and Krane RJ: The flow rate nomo- gram: 1. Development, J Urol 122: 665 (1979).

7. Abrams PH: Prostatism and prostatectomy: The value of urine flow rate measurement in the pre-operative assessment for operation, ibid 117: 70 (1977).

8. George NJR, Feneley RCL, and Robert JBM: Identification of the poor-risk patient with “prostatism” and detrusor failure, Br J Uro158: 299 (1986).

9. ‘Ihrner-Warwick RT, et al: A urodynamic view of prostatic obstruction and the results of prostatectomy, ibid 45: 631 (1973).

10. Andersen JT, Jacobsen 0, and Strandgaard L: The diagnostic value of intravenous pyelography in infravesical ob- - _ . .&&ion in males, Stand J Urol Nephrol 11: 225 (1977).

11. Bauer DL. Garrison RW. and McRoberts IW: The health and cost implications of routine excretory urography before trans- urethral prostatectomy, J Urol 123: 386 (1989).

12. Manoliu RA: Urethral patterns on micturition cys- tourethrography in adult males, Fortschr Rontgenste 134: 545 (1981).

13. Jacobsen 0, and Andersen JT: Functional bladder neck ob- struction. Voiding cystourethrography and pressure flow measurements, Acta Radio1 Diagn 23: 611 (1982).

14. Mathews PN, et al: The use of ultrasound in the investiga- tion of prostatism, Br J Uro154: 536 (1982).

15. Abrams PH, and Feneley RCL: The significance of the symptoms associated with bladder outflow obstruction, Urol Int 33: 171 (1978).

16. Drake WM Jr: The uroflowmeter: An aid to the study of the lower urinary tract, J Uro159: 650 (1948).

17. Von Garrelts BG: Analysis of micturition-a new method of recording the voiding of the bladder, Acta Chir Stand 112: 326 (1956).

18. International Continence Society: Third report and the standardization of terminology of lower urinary tract function, Br J Urol 52: 348 (1989).

19. Abrams PH, and Griffith DJ: The assessment of prostatic obstruction from urodynamic measurements and from residual urine, ibid 51: 129 (1979).

20. Bauman W: Prufung der Blasenphysiologie mit Cystomet- rie and Sphincterometrie, Urol Int 1: 427 (1955).

21. Murphy JJ, and Schoenberg HW: Observations on intra- vesical nressure chances durine micturition, I Uro184: 196 (1966).

22. Webster GD, &rd Old& RA: Value.of subtracted bladder pressure measurement in routine urodynamics, Urology 16: 656 (1980).

23. Ball AJ, Feneley RCL, and Abrams PH: The natural his- tory of untreated prostatism, Br J Uro153: 613 (1981).

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