Leak Point of Incontinence: A Measure of the Interaction between Outlet Resistance and Bladder Capacity

0022-534 7/93/1501-0162$03.00/0 THE JOURNAL OF UROLOGY Copyright© 1993 by AMERICAN UROLOGICAL ASSOCIATION, INC.

Vol. 150, 162-164, July 1993

Printed in U.S.A.

LEAK POINT OF INCONTINENCE: A MEASURE OF THE INTERACTION BETWEEN OUTLET RESISTANCE AND BLADDER CAPACITY MICHAEL McCORMACK,* JOHN PIKE

AND

GEORGE KIRULUTA

From the Division of Pediatric Urology, Department of Surgery, Montreal Children's Hospital, McGill University, Montreal, Quebec, Canada

ABSTRACT

A total of 48 consecutive spina bifida patients undergoing routine urodynamic studies was classified into 2 groups depending upon whether they demonstrated uninhibited bladder contractions. Of the patients 34 demonstrated detrusor hyperreflexia and 14 had detrusor areflexia. These 2 groups were then subdivided depending on the continence status. Of the areflexic and hyperreflexic groups, 6 and 7 patients, respectively, were wet despite at least 2 years of conservative medical management. Leak point pressure and leak point volume were determined in all patients and results were compared in both subgroups. In the hyperreflexic groups leak point volume but not leak point pressure was significantly different between the wet and dry patients. The areflexic group demonstrated the opposite finding, that is the leak point pressure but not the leak point volume was significantly different between wet and dry patients. From these studies we determined that in the areflexic group leak point pressure was useful to predict incontinence, whereas in the hyperreflexic group leak point volume was more useful. The addition of the measurement of leak point pressure and leak point volume during routine urodynamic studies in myelodysplastic patients enhances accurate diagnosis and may select those who will best benefit from bladder augmentation and/or a procedure to increase outlet resistance. KEY WORDS: urodynamics, urinary incontinence, spinal dysraphism

Urethrovesical dysfunction in children with spina bifida presents clinically as either upper urinary tract deterioration or urinary incontinence. Recent medical advances, including the use of clean intermittent catheterization and various forms of pharmacological manipulation, have permitted more efficient management of both problems. Geraniotis et al demonstrated that intermittent catheterization, when used prophylactically in spina bifida patients, decreased the incidence of upper urinary tract deterioration from an expected 50 to 10%.' Similarly, the use of intermittent catheterization and/or anticholinergic medication has allowed many previously incontinent patients to attain continence. 2 In nearly a third of all spina bifida patients, however, incontinence is poorly controlled with standard management regimens and surgical correction of the incontinence is subsequently considered. Surgical measures include the various forms of augmentation enterocystoplasty, 3 which increase the storage ability of the bladder, or if the patient has sphincteric incompetence a procedure to increase outlet resistance is done, such as urethral sling,4· 5 artificial urinary sphincter,6 YoungDees bladder neck reconstruction 7 or Kropp procedure. 8 In practice, however, it is not always clear which surgical procedure will best benefit a particular patient. To investigate the factors predisposing to urinary incontinence, various uroradiological procedures and urodynamic parameters are obtained. Ideally, what is needed is a measure of the volume and pressure in the system at the moment of incontinence, so that a functional estimate of bladder capacity and outlet resistance is obtained. McGuire et al described the use of leak point pressure, the intravesical pressure at the time of urethral leakage, as a means to prognosticate risk of upper urinary tract deterioration in myelodysplastic children. 9 We examined the use of leak point Accepted for publication December 11, 1992. * Current address: Hopital du Haut-Richelieu, 920 Bou!. du Seminaire, Saint-Jean-sur-Richelieu, Quebec, J3A 1B7 Canada.

measurements, including leak point volume, hyperactivity and so forth, as potential simple and reliable urodynamic parameters that could help assess the etiology and severity of incontinence, and subsequently influence guidelines for appropriate surgical management. MATERIALS AND METHODS

We reviewed 48 consecutive spina bifida patients undergoing routine urodynamic studies (25 boys and 23 girls, with a mean age of 9 years, range 6 to 15). Each patient was evaluated for significant urinary tract infection by assessment of symptoms and urine dipstick cultures. Only patients who were asymptomatic and negative for nitrate on dipstick evaluation were evaluated. The patients were divided into 2 distinct groups based upon a cystometric analysis of the bladder activity. Group 1 consisted of 34 patients who demonstrated uninhibited bladder contractions and, thus, had detrusor hyperreflexia, and group 2 consisted of 14 patients with bladder areflexia. These 2 groups were then subdivided according to the severity of the incontinence (fig. 1). Dry patients included those whose SPINA BIFIDA PATIENTS UNDERGOING ROUTINE URODYNAMIC STUDIES (N

=

48)

GROUP I HYPERREFLEXIA (N=34)

I \

GROUP II AREFLEXIA (N=l4)

I \

WET

DRY

WET

DRY

( 7)

(27)

(6)

( 8)

FIG. 1. Continence status of patients based on cystometric findings

162

LEAK POINT PRESSURE

incontinence was controlled by conservative methods, such as clean intermittent catheterization and/or anticholinergic medication. Wet patients were those with incontinence unresponsive to clean intermittent catheterization and anticholinergic medication, and they invariably used diapers. Therefore, there were 4 groups of patients: hyperreflexic dry, hyperreflexic wet, areflexic dry and areflexic wet. The mean age for each group was similar (9 years). During urodynamic assessment leak point measurements were determined in all patients by measuring bladder pressure and volume through an 8F double lumen urethral catheter. The rate of infusion during cystometric studies was 25 ml. per minute at room temperature. Patients were placed in the supine position during bladder filling. The leak point pressure and leak point volume were defined as the bladder pressure and volume, respectively, at which leakage from the urethral meatus was observed during bladder filling. The leak point pressure and leak point volume were then compared in each of the 2 subgroups to determine whether there was a significant difference in the values between continent and incontinent patients. Statistical analysis was performed with Student's t test. To corroborate the significance of leak point measurements in surgically treated patients, the charts and urodynamic studies of 25 spina bifida patients who previously underwent an operation for medically intractable urinary incontinence were reviewed. RESULTS

Of the 34 patients with bladder hyperreflexia 27 were dry and 7 were wet. Leak point pressure and leak point volume were determined for all patients (see table). There was no significant difference in the leak point pressure between wet and dry patients (44.5 cm. water and 48 cm. water, respectively). However, there was a significant difference in the leak point volume between these 2 groups (average 84 cc in wet hyperreflexic patients and 155 cc in dry patients, p <0.05). Among patients with an areflexic bladder the differences in urodynamic leak point parameters appeared to be reversed. Leak point volume was not statistically different between wet and dry patients (144 cc and 165 cc, respectively). However, there was a statistically significant difference in the leak point pressure between these 2 groups (average 30 cm. water in wet areflexic patients and 57 cm. water in dry areflexic patients, p <0.05). Of the 25 patients who underwent a previous operation for intractable urinary incontinence 18 had bladder hyperreflexia and had undergone augmentation enterocystoplasty. Among these patients 16 were continent postoperatively. Interestingly, the 2 patients who remained incontinent postoperatively had a leak point pressure of less than 40 cm. water preoperatively, which suggests that in a subgroup of incontinent patients with bladder hyperreflexia and low leak point volume a leak point pressure may indicate the need to augment bladder capacity and outlet resistance to achieve continence. The remaining 7 patients had bladder areflexia and had undergone a procedure to increase outlet resistance (3 urethral sling procedures and 4 artificial urinary sphincters). Of the 7 patients 5 were continent postoperatively. The 2 failures had a leak point pressure of less than 40 cm. water postoperatively, Leak point measurements in relation to continence status Group 1-Hyperreflexia (34 pts.) Wet No. pts. Av. cm. water leak point pressure (range) Av. ml. leak point vol. (range)

7 44.5 (20-70) 84

Dry 27 48.5 (16-97)

Group 2-Areflexia (14 pts.) Dry

Wet 6 30 (8-45)

8

57

(10-124)

(18-176) 155.2 (45-350) 144 (59-234) 165.5 (88-252)

163 SPIJ,;P. BIFIDA PATIENT

INTRACTABLE URINARY INCONTINENCE

LPP AND LPV

HYPERREFLEXIA

AREFLEXIA

YES

YES

ere

PHARHACOLOGIC THERAPY +/- CIC

FIG. 2. Flow chart in management of patients with intractable urinary incontinence. LPP, leak point pressure. LPV, leak point volume. CIC, clean intermittent catheterization.

suggesting inadequate outlet resistance. Failure of the procedure was probably secondary to a failure to increase urethral resistance sufficiently. DISCUSSION

Urinary continence in the patient with neurogenic bladder dysfunction depends upon the interaction and balance between outflow resistance and functional bladder capacity. Depending upon the level and extent of the neurological lesion, there may be detrusor hyperreflexia, areflexia and decreased detrusor compliance, as well as an uncoordinated or inadequate sphincter mechanism. The majority of patients with myelodysplasia will have an areflexic or noncompliant bladder, an open internal sphincter and a relatively fixed external sphincter not under volitional control. 10 Previously, leak point pressure has been used to prognosticate the risk of upper urinary tract deterioration in myelodysplastic children. 9 This measurement is made possible by the fact that the sphincter apparatus in myelodysplastic patients is incompetent and subsequently urethral leakage will occur when intravesical pressure overcomes the outlet resistance. Measurement of leak point volume, the bladder volume at which urethral leakage occurs, is also useful in that it provides a measure of the functional capacity of the storage system. Given that the majority of patients with spina bifida have a fixed outlet resistance, it is of interest to examine the variable of bladder capacity in regard to continence. Patients with a low pressure, compliant system are more successful at urine storage than those with a high pressure, poorly compliant system, since the pressure needed to overcome outlet resistance is reached at a lower volume in the latter patients. This fact has led us to look more closely at the value of leak point measurements as a means of evaluating the system as a whole and, thus, allowing some insight into the interaction of the 2 main components of continence. Our data suggest that the mechanisms underlying incontinence in patients with detrusor hyperreflexia differ from those with detrusor areflexia. Patients with a hyperreflexic bladder could be placed into incontinent or continent groups by examining their leak point volume. Hyperreflexic bladders with leak point volumes of less than 100 cc were almost consistently incontinent. Statistically, leak point pressure was not a useful criterion for differentiation of these 2 groups. These results reflect the fact that incontinence in spina bifida patients often occurs with the onset of detrusor hyperreflexia or deterioration in bladder compliance. Hyperreflexia was apparent at low bladder volumes in the wet patients despite the use of various anticholinergic drugs. In the dry patients hyperreflexia either occurred at higher volumes (that is more than 100 cc) or had been controlled with anticholinergics and more frequent intermittent catheterizations. Thus, in spina bifida patients with bladder hyperreflexia the lack of functional bladder capacity

164

LEAK POINT PRESSURE

seems to be the underlying cause of incontinence. This fact has led us to consider a leak point volume of less than 100 cc in a hyperreflexic incontinent patient to be an indication for bladder augmentation. On the other hand, patients with an areflexic bladder could be placed into incontinent or continent groups by determining the leak point pressure. Areflexic bladders with leak point pressures of less than 40 cm. water were almost consistently incontinent. Statistically, leak point volume was not a useful criterion for differentiation of these 2 groups, which suggests that in the presence of a functionally capacious system a leak point pressure of 40 cm. water or greater is necessary to maintain continence. During our investigations in patients with incontinence we have observed that although many maintain continence while in the supine position at an intravesical pressure of less than 40 cm. water, a change to a sitting or upright position results in urinary leakage. Urodynamically, this change in posture is associated with a 10 to 15 cm. water increase in intra-abdominal pressure. Subsequently, we consider a leak point pressure of less than 55 cm. water as a criterion to try and bolster outlet resistance. There also appears to be a small but important subgroup of patients, generally those with detrusor hyperreflexia but in eluding patients with a poorly compliant areflexic bladder, who have low leak point pressure and leak point volume. These patients probably require bladder augmentation plus a procedure to increase outlet resistance to attain continence (fig. 2). In summary, leak point pressure and leak point volume are useful criteria to determine the efficiency of bladder capacity and sphincter function during bladder filling in myelodysplastic children. Moreover, these parameters are easily obtained and

reproducible. We recommend their use as a guide for surgical management. REFERENCES

1. Geraniotis, E., Koff, S. A. and Enrile, B.: The prophylactic use of clean intermittent catheterization in the treatment of infants and young children with myelomeningocele and neurogenic bladder dysfunction. J. Urol., 139: 85, 1988. 2. Webster, G.D., el-Mahrouky, A., Stone, A. R. and Zakrzewski, C.: The urological evaluation and management of patients with myelodysplasia. Brit. J. Urol., 58: 261, 1986. 3. Hinman, F., Jr.: Selection of intestinal segments for bladder substitution: physical and physiological characteristics. J. Urol., 139: 519, 1988. 4. Raz, S., McGuire, E. J., Ehrlich, R. M., Zeidman, E. J., Wang, S. C., Alarcon, A., Schmidtbauer, C. and McLaughlin, S.: Fascia! sling to correct male neurogenic sphincter incompetence: the McGuire/Raz approach. J. Urol., 139: 528, 1988. 5. Woodside, J. R. and Borden, T. A.: Pubovaginal sling procedure for the management of urinary incontinence in a myelodysplastic girl. J. Urol., 127: 744, 1982. 6. Light, K. J., Hawila, M. and Scott, F. B.: Treatment of urinary incontinence in children: the artificial sphincter versus other methods. J. Urol., 130: 518, 1983. 7. Johnson, H. W., Weckworth, P. F., Coleman, G. U., Arnold, W. J., Sawatzky, B. J., Moloney, P. J. and Stewart, D.: Bladder-outlet reconstruction in neurogenic bladder due to myelomeningocele. Canad. J. Surg., 31: 22, 1988. 8. Kropp, K. A. and Angwafo, F. F.: Urethral lengthening and reimplantation for neurogenic incontinence in children. J. Urol., 135: 533, 1986. 9. McGuire, E. J., Woodside, J. R., Borden, T. A. and Weiss, R. M.: Prognostic value of urodynamic testing in myelodysplastic patients. J. Urol., 126: 205, 1981. 10. Bloom, D. A. and McGuire, E. J.: Practical management of children with myelomeningocele. Dial. Ped. Urol., vol. 12, pp. 3-4, June 1989.