- Email: [email protected]
ESTIMATING DETRUSOR PRESSURE AT HOME IN PEDIATRIC PATIENTS WITH MYELOMENINGOCELE
0022-5347/99/1624-1410/0
Vol. 162, 1410-1414, October 1999 Printed in U.S.A.
THE JOURNAL OF UaOtOcY
Copyright 0 1999 by AMeRlc.m UROLOGICAL ASSOCIATION, Iac
ESTIMATING DETRUSOR PRESSURE AT HOME IN PEDIATRIC PATIENTS WITH MYELOMENINGOCELE MARGOT S. DAMASER,*.t KIM BRZEZINSKI, JAMES S. WALTER, JOHN S. WHEELER, LISA SCHLEHAHN SCHROEDER AND DAVID A. HATCH From the Hines Veterans Affairs Hospital, Hines and Department of Urology, Loyola University Medical Center, Maywwd, Illinois
ABSTRACT
Purpose: We evaluated a method of estimating detrusor pressure a t home in patients with myelomeningocele who perform clean intermittent catheterization to empty the bladder. Materials and Methods: Patients with myelomeningocele who perform clean intermittent catheterization underwent cystometry. At home they determined bladder pressure before draining a full bladder and after partial draining with the bladder almost empty. Home estimate of detrusor pressure was calculated using the formula, full bladder pressure - almost empty bladder pressure. Results: A total of 4 boys and 5 girls with a mean age plus or minus standard deviation of 9.6 ? 7.9 years who were enrolled in our study made 16.9 2 15.2 home bladder pressure and volume recordings weekly each during a mean of 5.8 -t 4.3 months. Mean bladder capacity determined at home was significantly greater than cystometric capacity (354 2 185 versus 250 2 146 ml.). At a mean home and cystometric volume of 190 t 110 ml. full bladder pressure a t home was not significantly different from cystometric vesical pressure (31.0 ? 8.8 versus 27.5 2 7.5 cm. water). At a mean volume of 23 ? 15 ml. mean home almost empty bladder pressure was not significantly different from cystometric abdominal pressure a t full and almost empty volumes (14.1 5 5.5 versus 17.0 +- 7.4 and 15.5 2 5.8 cm. water). Mean home estimate of detrusor pressure was not significantly different from cystometric detrusor pressure (17.0 ? 6.3 versus 10.2 9.2 cm. water). Conclusions: Estimation of detrusor pressure at home is reliable and accurate in patients who perform clean intermittent catheterization. These pressure determinations may be used as a baseline for rapid identification of changes in bladder function. KEYWORDS:abnormalities, meningomyelocele, bladder, urodynamics
Patients with myelomeningocele are at risk for high bladder pressure, which may indicate a tethered spinal cord and is associated with upper urinary tract deterioration, urinary tract infection, vesicoureteral reflux and renal insufficienCY.'-~ As they age, pediatric patients are particularly susceptible to changes in bladder function due to spinal cord tethering or hyperreflexia, which may require changing the dose of m e d i ~ a t i o n . ~The - ~ most significant source of urologicd morbidity and mortality in patients with myelomeningocele is renal failure secondary to upper tract deterioration due to high bladder pressure.' Cystometry is done to evaluate bladder function in patients with myelomeningocele.s Those in whom cystometric leak point pressure is greater than 40 cm. water are a t significant risk for upper tract deteri~ration.~ Early detection of high bladder pressure may prevent irreversible bladder injury, reflux and upper tract deterioration" but cystometry is timeconsuming, invasive and expensive, which limits the frequency with which it is performed. The diagnosis of high bladder pressure is currently based on cystometric measurement of detrusor pressure, as calculated using the formula, bladder or vesical pressure - abdominal pressure. In
cystometry rectal pressure is used to estimate abdominal pressure. We have developed a small hand-held pressure that may be used at home for serial bladder pressure measurement in patients who perform clean intermittent catheterization to empty the bladder. We previously noted that in patients with myelomeningocele home bladder pressure accurately reflects vesical pressure." In our previous study home bladder pressure was low at small volume and similar to abdominal pressure. However, pressure measured with the bladder empty did not correlate well with cystometric abdominal pressure. Therefore, in our current study we tested the hypothesis that almost empty bladder pressure may be used to approximate abdominal pressure when estimating detrusor pressure at home. MATERIALS AND METHODS
Patients with neurogenic bladder caused by myelomeningocele or spinal cord damage who perform clean intermittent catheterization were recruited from those treated at our multidisciplinary spina bifida clinic. Study exclusion criteria were posterior urethral valves, bladder augmentation, no clean intermittent catheterization and a catheterizable stoma. Patients and families were instructed t o connect the home bladder pressure recording equipment, consisting of a mechanical bellows pressure gauge, an antireflux valve and connecting tubing, with a universal connector. They then attached it to the open end of the bladder catheter immediately before the first morning clean intermittent catheteriza-
Accepted for publication May 14, 1999. Su ported by Veterans Administration Rehabilitation Research and gevelopment Grants B95-861A, and Department of Urology, Loyola University Medical Center. * Requests for reprints: Research Service (151).Hines Veterans Administration Hospital, Hines, Illinois 60141. t Reci ient of Veterans Administration Advanced Rehabilitation Researci Career Development Award. 1410
ESTIMATING DETRUSOR PRESSURE AT HOME IN MYELOMENINGOCELE CASES
tion once weekly, as described previously." One patient used a digital pressure gauge but all other methods were identical. Patients inserted the catheter into the bladder and recorded bladder pressure with a full bladder before emptying. They detached the gauge from the catheter and drained the bladder until urine stopped flowing and began t o drip. Patients recorded the volume drained and reattached the gauge to record almost empty bladder pressure. They then detached the pressure gauge and emptied the bladder fully, recording the total volume drained. Volume at almost empty pressure was calculated using the formula, total volume drained volume drained until almost empty. No rectal catheters were used at home. Therefore, we hypothesized that almost empty bladder pressure may be used to approximate abdominal pressure. Home estimate of detrusor pressure was calculated using the formula, full bladder pressure - almost empty bladder pressure. Bladder capacity at home was defined as the greatest total bladder volume drained by clean intermittent catheterization at home. When recording pressure, patients were instructed to watch until the pressure gauge stopped changing and record the steady state value. They were also instructed to perform home monitoring always in the same position and not bear down, cough or move during pressure recording. Patient position during measurement, medication changes, episodes of urinary tract infection, leakage between clean intermittent catheterizations and difficult bowel function were noted at each measurement. Cystometry was performed in each patient at the beginning of the study using previously described methods.12 Briefly, the bladder was catheterized with a 6 or 8F double lumen catheter depending on patient age and size. The rectum was catheterized with an 8F nonlatex balloon catheter filled with 1 to 2 cm. of water. Depending on patient age, predicted bladder capacity andor history of residual urine volume, the bladder was filled with sterile water at 4 to 20 ml. per minute, calculated to fill the bladder to capacity in 10 to 20 minutes.13 During cystometry each patient was placed in the position used at home to record home bladder pressure. Bladder and rectal pressures were recorded using a urodynamics system. Rectal pressure was used to approximate abdominal pressure. Detrusor pressure was determined using the formula, vesical pressure - rectal pressure at the same volume. Filling continued until water leaked around the catheter or the patient had a strong sensation of fullness at cystometric capacity. Pressure was compared a t the volumes at which home bladder and cystometric pressures were recorded. Home full and detrusor pressures were compared with cystometric vesical and detrusor pressures at the same volume, respectively. Home almost empty pressure was compared with cystometric abdominal pressure at volumes of fill and almost empty bladder pressure recording. In all patients data were combined by initially calculating the mean value per individual. To determine a measurement of compliance for comparing home and cystometry data we fit a line to pressure-volume data from home recordings and cystometry, as described previously.'* Results are presented as mean plus or minus standard deviation (SD). Statistically significant differences were determined using the paired Student t test or analysis of variance followed by Dunn's test when more than 2 parameters were compared with p C0.05 considered statistically significant. RESULTS
A total of 4 boys and 5 girls 1.3 to 23.7 years old (mean age 9.6 f 7.9) a t cystometry underwent 1 or 2 cystometrograms and made a mean of 16.9 ? 15.2 home bladder pressure and volume recordings weekly during a mean of 5.8 ? 4.3 months. The etiology of neurogenic bladder was myelomeningocele in
1411
8 cases and nerve root injury secondary to corrective scoliosis surgery in 1. All 9 patients received medication to decrease detrusor contractions, including oxybutynin in 6, combined oxybutynin and imipramine in 2, and imipramine only in 1. Urodynamic studies performed while patients were on anticholinergic medication showed no significant low volume uninhibited bladder contractions. On the medical and catheterization regimens 6 patients were relatively continent of urine, such that they wore regular underwear without incontinence pads. Two young patients were incontinent and in diapers, and 1 was incontinent despite catheterization every 2 to 3 hours. There was some variation in home bladder pressure recording at each volume (see figure). However, the variation of bladder pressure at home did not correlate with reported urinary tract infection or medication change. In 4 patients a mean of 0.6 2 0.7 episode of symptomatic urinary tract infection each was treated during the study but no significant change in recorded pressure was associated with the episode. In 7 of the 9 patients home and cystometric pressure was recorded in the same position, while in the remaining 2 postural variation may explain some variability in home bladder pressure recording. Mean bladder capacity was significantly greater at home than during cystometry (354 2 158 versus 250 f 146 ml., p <0.05). Because of increased capacity at home, only a mean of 44 f 24% of home full bladder pressure recordings were made at a volume less than cystometric capacity. Since home and cystometric bladder pressure should be statistically correlated only at comparable volumes, only the 44% of home full bladder pressure recordings made at a volume less than cystometric capacity were used for comparison. Despite the variability in home pressure recordings home pressure correlated well with cystometric pressure. At a mean home and cystometric volume of 190 2 110 ml. full bladder pressure at home was not significantly different from cystometric vesical pressure (31.0 2 8.8 versus 27.5 2 7.5 cm. water). Mean home estimate of detrusor pressure was not significantly different from cystometric detrusor pressure (17.0 f 6.3 versus 10.2 f 9.2 cm. water). At a mean volume of 23 f 15 ml. mean home almost empty bladder pressure was not significantly different from cystometric abdominal pressure at full and almost empty volumes (14.1 2 5.5 versus 17.0 f 7.4 and 15.5 2 5.8 cm. water. There was no significant difference in the variation of bladder pressure data in patients who used the analog or digital gauge. Slope of the line fits to home full, almost empty and estimated detrusor pressure-volume data were not significantly different from those t o cystometric vesical, abdominal and detrusor data, respectively (see table). The slope of all 3 home pressure-volume data sets were within 1 SD of 0 and, therefore, they were not significantly different from 0. The slope of cystometric abdominal data was also not significantly different from 0. In contrast, the slopes of cystometric vesical and detrusor data were greater than 1 SD above 0.
DISCUSSION
Early treatment of bladder pressure 30 cm. water or higher may prevent upper tract deteri~ration.~ In addition, early intervention increases the potential benefit of spinal cord untethering and high bladder pressure treatment in patients with myelomeningocele.'. l4 Cystometry is the standard test to determine bladder function and high bladder pressure.' However, because cystometry is expensive, invasive and time-consuming, it is not performed often. We previously presented a simple home pressure gauge, so that patients who perform clean intermittent catheterization may determine serial bladder pressure in a convenient and comfortable manner.'* We report a new method for estimating detrusor
ESTIMATING DETRUSOR PRESSURE AT HOME IN MYELOMENINGOCELE CASES
1412 75
50 25
Detrusor Pressure
1
-
0. 0 .
050
25
75
100
150
125
175
CMG Vesical Pressure Home Full Pressures
L
0
p! 25
a
0.
-
0 0
u) v)
p! a
00
50
25
75
100
125
150
175
CMG Abdominal Pressure Home Almost Empty Pressures
,El Home
0
25
50
75
100
125
150
175
Volume (ml)
Cystometry (CMG) and home bladder pressure in typical patient Slope of line fits to home and cystometry pressure-uolume data Mean Cm. Water/Ml. 2 SD
Full bladder/vesical slope Detrusor slope Almost empty bladdedabdominal slope
Home
Cystometry
0.04 0.06 0.04 2 0.06 0.01 -t 0.183
0.07 2 0.03 0.06 ? 0.03 0.01 2 0.03
pressure at home using the home pressure monitoring system previously developed. Nine subjects measured detrusor pressure at home without technical difficulty or complications. In this study estimating detrusor pressure was more complex than previous home because of the need to deterbladder pressure mine almost empty bladder pressure and volume. However, according to monthly telephone calls made to obtain weekly data patient compliance was high. As observed previously,'2, l5 bladder capacity at home was greater than cystometric capacity, which is likely due to the increased filling rate, uncomfortable clinic setting and rectal catheter, and room temperature water infused during cystometry.16-18 Full bladder pressure is the most accurate recording made at home and it did not differ significantly from cystometric vesical pressure despite the more rapid filling rate and uncomfortable conditions during cystometry. Similarly there were no significant differences between home almost empty bladder pressure and cystometric abdominal pressure, nor between home estimate of detrusor pressure and cystometric detrusor pressure. In our previous study abdominal pressure was approximated a t home by empty bladder pressure.'2 In contrast to the results of the current study, the estimate of detrusor pressure at home in our previous study was significantly greater than cystometric detrusor pressure due to inaccuracies in the estimation of abdominal pressure at home that have been corrected in the current study. As demonstrated previously,". l2 bladder pressure meas-
ured a t home was not identical when measured again a t the same volume even in the same patient in the same position. While this variation may be due to errors when reading the analog pressure gauge, it is consistent with the study of Griffiths et a1 in which ambulatory monitoring techniques demonstrated normal variations in bladder pressure. l9 Jensen observed this variability of bladder pressure in repeat cystometry measurements,20 which may be caused by different filling rates due to diuresis or different patient positions during home recording. In our subjects these pressure variations did not correlate with infection or constipation. By monitoring once weekly any transient changes due to infection or constipation may have been missed. However, weekly, monthly or annual monitoring may prove useful for determining long-term trends, such as those due to spinal tethering or deteriorating bladder function. As the medical conditions of our patients were stable, they represented appropriate subjects for establishing method reliability. Future studies are needed to determine whether home bladder pressure accurately reflects changes in urological clinical condition. Because of the discrete nature of home pressure recording, we fit a line to the pressure-volume data t o compare bladder compliance a t home to that during cystometry. The inverse of the slope of the line fit is comparable to bladder compliance. The slope of line fits to home full and almost empty bladder, and estimated detrusor pressure-volume data were not significantly different from those to cystometric vesical, abdominal and detrusor data, respectively. This finding indicates that bladder compliance at home during a longer period is similar to that during cystometry. In addition, the slope of a line fit to home almost empty and cystometric abdominal pressure-volume data was not significantly different from a horizontal line with a slope equal to 0. This observation implies that abdominal pressure may be estimated as a single pressure value at all volumes. Likewise home detrusor pressure may be estimated by subtracting a single abdominal pressure value from each measured home
1413
ESTIMATING DETRUSOR PRESSURE AT HOME IN MYELOMENINGOCELE CASES full bladder p r e s s u r e value. This abdominal pressure value m a y be determined by cystometry or by calculating the mean of several initial, almost e m p t y h o m e bladder pressure recordings made w i t h the p a t i e n t in the same position as during all subsequent home recordings. The a d v a n t a g e of this method would be t o simplify the home bladder pressure recording method, s u c h that only full bladder pressure would be recorded regularly. Without rectal pressure measurement it is impossible t o determine whether increased bladder pressure is due to det r u s o r contractions or increased abdominal p r e s s u r e secondary t o coughing or laughing. However, we instructed the patients t o be still and record bladder pressure only after it had reached a s t e a d y state value. Therefore, it is likely that our reported pressure data reflect neither d e t r u s o r contractions n o r increased abdominal pressure. D e t r u s o r pressure at h o m e and the slope of detrusor pressure-volume data did n o t differ significantly from cystom e t r i c d e t r u s o r pressure d a t a , suggesting that this method m a y be used t o e s t i m a t e frequently s t e a d y state detrusor pressure in this patient population w i t h o u t the inconvenience of cystometry. The power of the statistical tests used t o compare pressure and slope w a s n o t high enough t o discount the possibility of a statistical difference if more subjects were compared. Therefore, a large-scale clinical trial is needed t o determine conclusively w h e t h e r this method accur a t e l y e s t i m a t e s detrusor pressure. In addition, high h o m e d e t r u s o r pressure m u s t be correlated with renal function t o d e t e r m i n e whether there is a threshold h o m e detrusor press u r e , as in cystometry, above which renal dysfunction is likely t o develop. CONCLUSIONS
H o m e monitoring of bladder pressure c a n n o t be substituted for clinical cystometry, which is necessary for assessing basic urodynamics. However, in patients w h o perform clean intermittent catheterization t o e m p t y the bladder w e suggest that f r e q u e n t h o m e monitoring of bladder pressure m a y supplement cystometric recording for detecting increasing bladder pressure early. W e report a technique for accurately estimating d e t r u s o r pressure at h o m e using almost e m p t y bladder pressure t o approximate steady state abdominal pressure. This technique m a y be used as a baseline for r a p i d identification of a n y change in urological condition or as a screening examination for urodynamics.
Dr. L. S u z a n n e mom, Robert Walter and Paul Zaszczurynski provided assistance and expertise. REFERENCES
1. Kaplan, W. E., McLone, D. G. and Richards, I.: The urological
manifestations of the tethered spinal cord. J. Urol., 140 1285, 1988. 2. Flood, H. D., Ritchey, M. L., Bloom, D. A,, Huang, C. and McGuire, E. J.: Outcome of reflux in children with myelodysplasia managed by bladder pressure monitoring. J . Urol., 152 1574, 1994. 3. 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. 4. Dator, D. P.,Hatchett, L., Dyro, F. M., Shefner, J. M. and Bauer, S. B.: Urodynamic dysfunction in walking myelodysplastic children. J. Urol., 148.362, 1992. 5. Roach, M. B., Switter, D. M. and Stone, A. R.: The changing urodynamic pattern in infants with myelomeningocele. J . Urol., 150 944,1993. 6. Palmer, L. S., Richards, I. and Kaplan, W. E.: Subclinical changes in bladder function in children presenting with nonurological symptoms of the tethered cord syndrome. J. Urol., 159: 231,1998. 7. Fone, P. D., Vapnek, J. M., Litwiller, S. E., Couillard, D. R., McDonald, C. M., Boggan, J . E. and Stone, A. R.: Urodynamic
findings in the tethered spinal cord syndrome: does surgical release improve bladder function? J . Urol., 151: 604,1997. 8. Hunt, G. M.: Open spina bifida: outcome for a complete cohort treated unselectively and followed into adulthood. Dev. Med. Child Neurol., 3 2 108, 1990. 9. Stone, A. R.: Neurourologic evaluation and urologic management of spinal dysraphism. Neurosurg. Clin. N. Amer., 6269,1995. 10. Spindel, M. R., Bauer, S. B., Dyro, F. M., Drarup, C., Khoshbin, S.,Winston, K. R., Lebowitz, R. L., Colodny, A. H. and Retik, A. B.: The changing neurologic lesion in myelodysplasia. J.A.M.A., 258 1630,1987. 11. Walter, J. S.,Wheeler, J . S., Markley, J., Chintam, R., Blacker, L. M. and Damaser, M. S.: Home monitoring of bladder pressure and volume in individuals with spinal cord injury and multiple sclerosis. J . Spinal Cord Med., 21: 7, 1998. 12. Andros, G. J., Hatch, D. A,, Walter, J. S., Wheeler, J . S., Schlehahn, L. and Damaser, M. S.: Home bladder pressure monitoring in children with myelomeningocele. J . Urol., 160: 518,1998. 13. Berger, R. M., Maizels, M., Moran, G. C., Conway, J. J. and Firlit, C. F.: Bladder capacity (ounces) equals age (years) plus 2 predicts normal bladder capacity and aids in diagnosis of abnormal voiding patterns. J . Urol., 129: 347,1983. 14. Lais, A,, Kasabian, N. G., Dyro, F. M., Scott, R. M., Kelly, M. D. and Bauer, S. B.: The neurosurgical implications of continuous neurourolo!zical surveillance of children with mvelodvsolasia. .. J. Urol., 163: 1879,1993. 15. Webb. R. J.. Griffiths. C. J.. Ramsden. P. D. and Neal, D. E.: Ambulatoj monitoring of bladder pressure in low compliance neurogenic bladder dysfunction. J . Urol., 148: 1477,1992. 16. Joseph, D. B.: The effect of medium-fill and slow-fill saline cystometry on detrusor pressure in infants and children with myelodysplasia. J . Urol., 141: 444,1992. 17. McGuire, E. J., Cespedes, R. D., Cross, C. A. and OConnell, H. E.: Videourodynamic studies. Urol. Clin. N. Amer., 2 3 309, 1996. 18. Geirsson, G. and Fall, M.: The ice-water test in the diagnosis of detrusor-external sphincter dyssynergia. Scand. J . Urol. Nephrol., 2 9 457, 1995. 19. Grifiths, C. J., Assi, M. S., Styles, R. A,, Ramsden, P. D. and Neal, D. E.: Ambulatory monitoring of bladder and detrusor pressure during natural filling. J . Urol., 142 780,1989. 20. Jensen, D.: Pharmacological studies of the uninhibited neurogenic bladder I. the influence of repeated filling and various filling rates on the cystometrogram of neurological patients with normal and uninhibited neurogenic bladder. Acta Neurol. Scand., 64:145,1981.
-
EDITORIAL COMMENT This report provides the clinician who treats patients with bladder dysfunction the ability to monitor more carefully potential changes in detrusor function than is afforded by conventional cystometry. This technique originally espoused by the authors (references 11 and 12 in article) has been modified somewhat to improve the accuracy of determining detrusor pressure. The authors did not measure intravesical pressure when the bladder was completely empty and used that measurement as abdominal pressure, which is subtracted from the intravesical pressure obtained when the bladder is full to calculate true detrusor pressure at capacity. Instead, they measured intravesical pressure with the bladder almost but not completely empty. They believe that this provides a more accurate measurement of abdominal pressure. They then compared this pressure measurement obtained at home to abdominal pressure recorded by a rectal balloon catheter placed at cystometrography in the hospital setting and noted little difference between these measurements. Thus, they assumed that the instructions to patients for determining abdominal pressure at home were accurate and reproducible. Why did they not record the pressure of the almost empty bladder at the hospital as well in the same manner as the patients did at home, and compare all determinations for accuracy and reproducibility? Be that as it may, this technique for home monitoring of detrusor filling pressure determined during natural filling is a useful tool for monitoring changes in lower urinary tract function and for identifjmg as early as possible patients at risk for upper urinary tract deterioration because of the easy accessibility of recording such changes in pressure. This idea is a natural extension of the concept of pressure at residual volume initially promulgated by Kaefer et al.1 They recorded bladder
Vol. 162, 1410-1414, October 1999 Printed in U.S.A.
THE JOURNAL OF UaOtOcY
Copyright 0 1999 by AMeRlc.m UROLOGICAL ASSOCIATION, Iac
ESTIMATING DETRUSOR PRESSURE AT HOME IN PEDIATRIC PATIENTS WITH MYELOMENINGOCELE MARGOT S. DAMASER,*.t KIM BRZEZINSKI, JAMES S. WALTER, JOHN S. WHEELER, LISA SCHLEHAHN SCHROEDER AND DAVID A. HATCH From the Hines Veterans Affairs Hospital, Hines and Department of Urology, Loyola University Medical Center, Maywwd, Illinois
ABSTRACT
Purpose: We evaluated a method of estimating detrusor pressure a t home in patients with myelomeningocele who perform clean intermittent catheterization to empty the bladder. Materials and Methods: Patients with myelomeningocele who perform clean intermittent catheterization underwent cystometry. At home they determined bladder pressure before draining a full bladder and after partial draining with the bladder almost empty. Home estimate of detrusor pressure was calculated using the formula, full bladder pressure - almost empty bladder pressure. Results: A total of 4 boys and 5 girls with a mean age plus or minus standard deviation of 9.6 ? 7.9 years who were enrolled in our study made 16.9 2 15.2 home bladder pressure and volume recordings weekly each during a mean of 5.8 -t 4.3 months. Mean bladder capacity determined at home was significantly greater than cystometric capacity (354 2 185 versus 250 2 146 ml.). At a mean home and cystometric volume of 190 t 110 ml. full bladder pressure a t home was not significantly different from cystometric vesical pressure (31.0 ? 8.8 versus 27.5 2 7.5 cm. water). At a mean volume of 23 ? 15 ml. mean home almost empty bladder pressure was not significantly different from cystometric abdominal pressure a t full and almost empty volumes (14.1 5 5.5 versus 17.0 +- 7.4 and 15.5 2 5.8 cm. water). Mean home estimate of detrusor pressure was not significantly different from cystometric detrusor pressure (17.0 ? 6.3 versus 10.2 9.2 cm. water). Conclusions: Estimation of detrusor pressure at home is reliable and accurate in patients who perform clean intermittent catheterization. These pressure determinations may be used as a baseline for rapid identification of changes in bladder function. KEYWORDS:abnormalities, meningomyelocele, bladder, urodynamics
Patients with myelomeningocele are at risk for high bladder pressure, which may indicate a tethered spinal cord and is associated with upper urinary tract deterioration, urinary tract infection, vesicoureteral reflux and renal insufficienCY.'-~ As they age, pediatric patients are particularly susceptible to changes in bladder function due to spinal cord tethering or hyperreflexia, which may require changing the dose of m e d i ~ a t i o n . ~The - ~ most significant source of urologicd morbidity and mortality in patients with myelomeningocele is renal failure secondary to upper tract deterioration due to high bladder pressure.' Cystometry is done to evaluate bladder function in patients with myelomeningocele.s Those in whom cystometric leak point pressure is greater than 40 cm. water are a t significant risk for upper tract deteri~ration.~ Early detection of high bladder pressure may prevent irreversible bladder injury, reflux and upper tract deterioration" but cystometry is timeconsuming, invasive and expensive, which limits the frequency with which it is performed. The diagnosis of high bladder pressure is currently based on cystometric measurement of detrusor pressure, as calculated using the formula, bladder or vesical pressure - abdominal pressure. In
cystometry rectal pressure is used to estimate abdominal pressure. We have developed a small hand-held pressure that may be used at home for serial bladder pressure measurement in patients who perform clean intermittent catheterization to empty the bladder. We previously noted that in patients with myelomeningocele home bladder pressure accurately reflects vesical pressure." In our previous study home bladder pressure was low at small volume and similar to abdominal pressure. However, pressure measured with the bladder empty did not correlate well with cystometric abdominal pressure. Therefore, in our current study we tested the hypothesis that almost empty bladder pressure may be used to approximate abdominal pressure when estimating detrusor pressure at home. MATERIALS AND METHODS
Patients with neurogenic bladder caused by myelomeningocele or spinal cord damage who perform clean intermittent catheterization were recruited from those treated at our multidisciplinary spina bifida clinic. Study exclusion criteria were posterior urethral valves, bladder augmentation, no clean intermittent catheterization and a catheterizable stoma. Patients and families were instructed t o connect the home bladder pressure recording equipment, consisting of a mechanical bellows pressure gauge, an antireflux valve and connecting tubing, with a universal connector. They then attached it to the open end of the bladder catheter immediately before the first morning clean intermittent catheteriza-
Accepted for publication May 14, 1999. Su ported by Veterans Administration Rehabilitation Research and gevelopment Grants B95-861A, and Department of Urology, Loyola University Medical Center. * Requests for reprints: Research Service (151).Hines Veterans Administration Hospital, Hines, Illinois 60141. t Reci ient of Veterans Administration Advanced Rehabilitation Researci Career Development Award. 1410
ESTIMATING DETRUSOR PRESSURE AT HOME IN MYELOMENINGOCELE CASES
tion once weekly, as described previously." One patient used a digital pressure gauge but all other methods were identical. Patients inserted the catheter into the bladder and recorded bladder pressure with a full bladder before emptying. They detached the gauge from the catheter and drained the bladder until urine stopped flowing and began t o drip. Patients recorded the volume drained and reattached the gauge to record almost empty bladder pressure. They then detached the pressure gauge and emptied the bladder fully, recording the total volume drained. Volume at almost empty pressure was calculated using the formula, total volume drained volume drained until almost empty. No rectal catheters were used at home. Therefore, we hypothesized that almost empty bladder pressure may be used to approximate abdominal pressure. Home estimate of detrusor pressure was calculated using the formula, full bladder pressure - almost empty bladder pressure. Bladder capacity at home was defined as the greatest total bladder volume drained by clean intermittent catheterization at home. When recording pressure, patients were instructed to watch until the pressure gauge stopped changing and record the steady state value. They were also instructed to perform home monitoring always in the same position and not bear down, cough or move during pressure recording. Patient position during measurement, medication changes, episodes of urinary tract infection, leakage between clean intermittent catheterizations and difficult bowel function were noted at each measurement. Cystometry was performed in each patient at the beginning of the study using previously described methods.12 Briefly, the bladder was catheterized with a 6 or 8F double lumen catheter depending on patient age and size. The rectum was catheterized with an 8F nonlatex balloon catheter filled with 1 to 2 cm. of water. Depending on patient age, predicted bladder capacity andor history of residual urine volume, the bladder was filled with sterile water at 4 to 20 ml. per minute, calculated to fill the bladder to capacity in 10 to 20 minutes.13 During cystometry each patient was placed in the position used at home to record home bladder pressure. Bladder and rectal pressures were recorded using a urodynamics system. Rectal pressure was used to approximate abdominal pressure. Detrusor pressure was determined using the formula, vesical pressure - rectal pressure at the same volume. Filling continued until water leaked around the catheter or the patient had a strong sensation of fullness at cystometric capacity. Pressure was compared a t the volumes at which home bladder and cystometric pressures were recorded. Home full and detrusor pressures were compared with cystometric vesical and detrusor pressures at the same volume, respectively. Home almost empty pressure was compared with cystometric abdominal pressure at volumes of fill and almost empty bladder pressure recording. In all patients data were combined by initially calculating the mean value per individual. To determine a measurement of compliance for comparing home and cystometry data we fit a line to pressure-volume data from home recordings and cystometry, as described previously.'* Results are presented as mean plus or minus standard deviation (SD). Statistically significant differences were determined using the paired Student t test or analysis of variance followed by Dunn's test when more than 2 parameters were compared with p C0.05 considered statistically significant. RESULTS
A total of 4 boys and 5 girls 1.3 to 23.7 years old (mean age 9.6 f 7.9) a t cystometry underwent 1 or 2 cystometrograms and made a mean of 16.9 ? 15.2 home bladder pressure and volume recordings weekly during a mean of 5.8 ? 4.3 months. The etiology of neurogenic bladder was myelomeningocele in
1411
8 cases and nerve root injury secondary to corrective scoliosis surgery in 1. All 9 patients received medication to decrease detrusor contractions, including oxybutynin in 6, combined oxybutynin and imipramine in 2, and imipramine only in 1. Urodynamic studies performed while patients were on anticholinergic medication showed no significant low volume uninhibited bladder contractions. On the medical and catheterization regimens 6 patients were relatively continent of urine, such that they wore regular underwear without incontinence pads. Two young patients were incontinent and in diapers, and 1 was incontinent despite catheterization every 2 to 3 hours. There was some variation in home bladder pressure recording at each volume (see figure). However, the variation of bladder pressure at home did not correlate with reported urinary tract infection or medication change. In 4 patients a mean of 0.6 2 0.7 episode of symptomatic urinary tract infection each was treated during the study but no significant change in recorded pressure was associated with the episode. In 7 of the 9 patients home and cystometric pressure was recorded in the same position, while in the remaining 2 postural variation may explain some variability in home bladder pressure recording. Mean bladder capacity was significantly greater at home than during cystometry (354 2 158 versus 250 f 146 ml., p <0.05). Because of increased capacity at home, only a mean of 44 f 24% of home full bladder pressure recordings were made at a volume less than cystometric capacity. Since home and cystometric bladder pressure should be statistically correlated only at comparable volumes, only the 44% of home full bladder pressure recordings made at a volume less than cystometric capacity were used for comparison. Despite the variability in home pressure recordings home pressure correlated well with cystometric pressure. At a mean home and cystometric volume of 190 2 110 ml. full bladder pressure at home was not significantly different from cystometric vesical pressure (31.0 2 8.8 versus 27.5 2 7.5 cm. water). Mean home estimate of detrusor pressure was not significantly different from cystometric detrusor pressure (17.0 f 6.3 versus 10.2 f 9.2 cm. water). At a mean volume of 23 f 15 ml. mean home almost empty bladder pressure was not significantly different from cystometric abdominal pressure at full and almost empty volumes (14.1 2 5.5 versus 17.0 f 7.4 and 15.5 2 5.8 cm. water. There was no significant difference in the variation of bladder pressure data in patients who used the analog or digital gauge. Slope of the line fits to home full, almost empty and estimated detrusor pressure-volume data were not significantly different from those t o cystometric vesical, abdominal and detrusor data, respectively (see table). The slope of all 3 home pressure-volume data sets were within 1 SD of 0 and, therefore, they were not significantly different from 0. The slope of cystometric abdominal data was also not significantly different from 0. In contrast, the slopes of cystometric vesical and detrusor data were greater than 1 SD above 0.
DISCUSSION
Early treatment of bladder pressure 30 cm. water or higher may prevent upper tract deteri~ration.~ In addition, early intervention increases the potential benefit of spinal cord untethering and high bladder pressure treatment in patients with myelomeningocele.'. l4 Cystometry is the standard test to determine bladder function and high bladder pressure.' However, because cystometry is expensive, invasive and time-consuming, it is not performed often. We previously presented a simple home pressure gauge, so that patients who perform clean intermittent catheterization may determine serial bladder pressure in a convenient and comfortable manner.'* We report a new method for estimating detrusor
ESTIMATING DETRUSOR PRESSURE AT HOME IN MYELOMENINGOCELE CASES
1412 75
50 25
Detrusor Pressure
1
-
0. 0 .
050
25
75
100
150
125
175
CMG Vesical Pressure Home Full Pressures
L
0
p! 25
a
0.
-
0 0
u) v)
p! a
00
50
25
75
100
125
150
175
CMG Abdominal Pressure Home Almost Empty Pressures
,El Home
0
25
50
75
100
125
150
175
Volume (ml)
Cystometry (CMG) and home bladder pressure in typical patient Slope of line fits to home and cystometry pressure-uolume data Mean Cm. Water/Ml. 2 SD
Full bladder/vesical slope Detrusor slope Almost empty bladdedabdominal slope
Home
Cystometry
0.04 0.06 0.04 2 0.06 0.01 -t 0.183
0.07 2 0.03 0.06 ? 0.03 0.01 2 0.03
pressure at home using the home pressure monitoring system previously developed. Nine subjects measured detrusor pressure at home without technical difficulty or complications. In this study estimating detrusor pressure was more complex than previous home because of the need to deterbladder pressure mine almost empty bladder pressure and volume. However, according to monthly telephone calls made to obtain weekly data patient compliance was high. As observed previously,'2, l5 bladder capacity at home was greater than cystometric capacity, which is likely due to the increased filling rate, uncomfortable clinic setting and rectal catheter, and room temperature water infused during cystometry.16-18 Full bladder pressure is the most accurate recording made at home and it did not differ significantly from cystometric vesical pressure despite the more rapid filling rate and uncomfortable conditions during cystometry. Similarly there were no significant differences between home almost empty bladder pressure and cystometric abdominal pressure, nor between home estimate of detrusor pressure and cystometric detrusor pressure. In our previous study abdominal pressure was approximated a t home by empty bladder pressure.'2 In contrast to the results of the current study, the estimate of detrusor pressure at home in our previous study was significantly greater than cystometric detrusor pressure due to inaccuracies in the estimation of abdominal pressure at home that have been corrected in the current study. As demonstrated previously,". l2 bladder pressure meas-
ured a t home was not identical when measured again a t the same volume even in the same patient in the same position. While this variation may be due to errors when reading the analog pressure gauge, it is consistent with the study of Griffiths et a1 in which ambulatory monitoring techniques demonstrated normal variations in bladder pressure. l9 Jensen observed this variability of bladder pressure in repeat cystometry measurements,20 which may be caused by different filling rates due to diuresis or different patient positions during home recording. In our subjects these pressure variations did not correlate with infection or constipation. By monitoring once weekly any transient changes due to infection or constipation may have been missed. However, weekly, monthly or annual monitoring may prove useful for determining long-term trends, such as those due to spinal tethering or deteriorating bladder function. As the medical conditions of our patients were stable, they represented appropriate subjects for establishing method reliability. Future studies are needed to determine whether home bladder pressure accurately reflects changes in urological clinical condition. Because of the discrete nature of home pressure recording, we fit a line to the pressure-volume data t o compare bladder compliance a t home to that during cystometry. The inverse of the slope of the line fit is comparable to bladder compliance. The slope of line fits to home full and almost empty bladder, and estimated detrusor pressure-volume data were not significantly different from those to cystometric vesical, abdominal and detrusor data, respectively. This finding indicates that bladder compliance at home during a longer period is similar to that during cystometry. In addition, the slope of a line fit to home almost empty and cystometric abdominal pressure-volume data was not significantly different from a horizontal line with a slope equal to 0. This observation implies that abdominal pressure may be estimated as a single pressure value at all volumes. Likewise home detrusor pressure may be estimated by subtracting a single abdominal pressure value from each measured home
1413
ESTIMATING DETRUSOR PRESSURE AT HOME IN MYELOMENINGOCELE CASES full bladder p r e s s u r e value. This abdominal pressure value m a y be determined by cystometry or by calculating the mean of several initial, almost e m p t y h o m e bladder pressure recordings made w i t h the p a t i e n t in the same position as during all subsequent home recordings. The a d v a n t a g e of this method would be t o simplify the home bladder pressure recording method, s u c h that only full bladder pressure would be recorded regularly. Without rectal pressure measurement it is impossible t o determine whether increased bladder pressure is due to det r u s o r contractions or increased abdominal p r e s s u r e secondary t o coughing or laughing. However, we instructed the patients t o be still and record bladder pressure only after it had reached a s t e a d y state value. Therefore, it is likely that our reported pressure data reflect neither d e t r u s o r contractions n o r increased abdominal pressure. D e t r u s o r pressure at h o m e and the slope of detrusor pressure-volume data did n o t differ significantly from cystom e t r i c d e t r u s o r pressure d a t a , suggesting that this method m a y be used t o e s t i m a t e frequently s t e a d y state detrusor pressure in this patient population w i t h o u t the inconvenience of cystometry. The power of the statistical tests used t o compare pressure and slope w a s n o t high enough t o discount the possibility of a statistical difference if more subjects were compared. Therefore, a large-scale clinical trial is needed t o determine conclusively w h e t h e r this method accur a t e l y e s t i m a t e s detrusor pressure. In addition, high h o m e d e t r u s o r pressure m u s t be correlated with renal function t o d e t e r m i n e whether there is a threshold h o m e detrusor press u r e , as in cystometry, above which renal dysfunction is likely t o develop. CONCLUSIONS
H o m e monitoring of bladder pressure c a n n o t be substituted for clinical cystometry, which is necessary for assessing basic urodynamics. However, in patients w h o perform clean intermittent catheterization t o e m p t y the bladder w e suggest that f r e q u e n t h o m e monitoring of bladder pressure m a y supplement cystometric recording for detecting increasing bladder pressure early. W e report a technique for accurately estimating d e t r u s o r pressure at h o m e using almost e m p t y bladder pressure t o approximate steady state abdominal pressure. This technique m a y be used as a baseline for r a p i d identification of a n y change in urological condition or as a screening examination for urodynamics.
Dr. L. S u z a n n e mom, Robert Walter and Paul Zaszczurynski provided assistance and expertise. REFERENCES
1. Kaplan, W. E., McLone, D. G. and Richards, I.: The urological
manifestations of the tethered spinal cord. J. Urol., 140 1285, 1988. 2. Flood, H. D., Ritchey, M. L., Bloom, D. A,, Huang, C. and McGuire, E. J.: Outcome of reflux in children with myelodysplasia managed by bladder pressure monitoring. J . Urol., 152 1574, 1994. 3. 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. 4. Dator, D. P.,Hatchett, L., Dyro, F. M., Shefner, J. M. and Bauer, S. B.: Urodynamic dysfunction in walking myelodysplastic children. J. Urol., 148.362, 1992. 5. Roach, M. B., Switter, D. M. and Stone, A. R.: The changing urodynamic pattern in infants with myelomeningocele. J . Urol., 150 944,1993. 6. Palmer, L. S., Richards, I. and Kaplan, W. E.: Subclinical changes in bladder function in children presenting with nonurological symptoms of the tethered cord syndrome. J. Urol., 159: 231,1998. 7. Fone, P. D., Vapnek, J. M., Litwiller, S. E., Couillard, D. R., McDonald, C. M., Boggan, J . E. and Stone, A. R.: Urodynamic
findings in the tethered spinal cord syndrome: does surgical release improve bladder function? J . Urol., 151: 604,1997. 8. Hunt, G. M.: Open spina bifida: outcome for a complete cohort treated unselectively and followed into adulthood. Dev. Med. Child Neurol., 3 2 108, 1990. 9. Stone, A. R.: Neurourologic evaluation and urologic management of spinal dysraphism. Neurosurg. Clin. N. Amer., 6269,1995. 10. Spindel, M. R., Bauer, S. B., Dyro, F. M., Drarup, C., Khoshbin, S.,Winston, K. R., Lebowitz, R. L., Colodny, A. H. and Retik, A. B.: The changing neurologic lesion in myelodysplasia. J.A.M.A., 258 1630,1987. 11. Walter, J. S.,Wheeler, J . S., Markley, J., Chintam, R., Blacker, L. M. and Damaser, M. S.: Home monitoring of bladder pressure and volume in individuals with spinal cord injury and multiple sclerosis. J . Spinal Cord Med., 21: 7, 1998. 12. Andros, G. J., Hatch, D. A,, Walter, J. S., Wheeler, J . S., Schlehahn, L. and Damaser, M. S.: Home bladder pressure monitoring in children with myelomeningocele. J . Urol., 160: 518,1998. 13. Berger, R. M., Maizels, M., Moran, G. C., Conway, J. J. and Firlit, C. F.: Bladder capacity (ounces) equals age (years) plus 2 predicts normal bladder capacity and aids in diagnosis of abnormal voiding patterns. J . Urol., 129: 347,1983. 14. Lais, A,, Kasabian, N. G., Dyro, F. M., Scott, R. M., Kelly, M. D. and Bauer, S. B.: The neurosurgical implications of continuous neurourolo!zical surveillance of children with mvelodvsolasia. .. J. Urol., 163: 1879,1993. 15. Webb. R. J.. Griffiths. C. J.. Ramsden. P. D. and Neal, D. E.: Ambulatoj monitoring of bladder pressure in low compliance neurogenic bladder dysfunction. J . Urol., 148: 1477,1992. 16. Joseph, D. B.: The effect of medium-fill and slow-fill saline cystometry on detrusor pressure in infants and children with myelodysplasia. J . Urol., 141: 444,1992. 17. McGuire, E. J., Cespedes, R. D., Cross, C. A. and OConnell, H. E.: Videourodynamic studies. Urol. Clin. N. Amer., 2 3 309, 1996. 18. Geirsson, G. and Fall, M.: The ice-water test in the diagnosis of detrusor-external sphincter dyssynergia. Scand. J . Urol. Nephrol., 2 9 457, 1995. 19. Grifiths, C. J., Assi, M. S., Styles, R. A,, Ramsden, P. D. and Neal, D. E.: Ambulatory monitoring of bladder and detrusor pressure during natural filling. J . Urol., 142 780,1989. 20. Jensen, D.: Pharmacological studies of the uninhibited neurogenic bladder I. the influence of repeated filling and various filling rates on the cystometrogram of neurological patients with normal and uninhibited neurogenic bladder. Acta Neurol. Scand., 64:145,1981.
-
EDITORIAL COMMENT This report provides the clinician who treats patients with bladder dysfunction the ability to monitor more carefully potential changes in detrusor function than is afforded by conventional cystometry. This technique originally espoused by the authors (references 11 and 12 in article) has been modified somewhat to improve the accuracy of determining detrusor pressure. The authors did not measure intravesical pressure when the bladder was completely empty and used that measurement as abdominal pressure, which is subtracted from the intravesical pressure obtained when the bladder is full to calculate true detrusor pressure at capacity. Instead, they measured intravesical pressure with the bladder almost but not completely empty. They believe that this provides a more accurate measurement of abdominal pressure. They then compared this pressure measurement obtained at home to abdominal pressure recorded by a rectal balloon catheter placed at cystometrography in the hospital setting and noted little difference between these measurements. Thus, they assumed that the instructions to patients for determining abdominal pressure at home were accurate and reproducible. Why did they not record the pressure of the almost empty bladder at the hospital as well in the same manner as the patients did at home, and compare all determinations for accuracy and reproducibility? Be that as it may, this technique for home monitoring of detrusor filling pressure determined during natural filling is a useful tool for monitoring changes in lower urinary tract function and for identifjmg as early as possible patients at risk for upper urinary tract deterioration because of the easy accessibility of recording such changes in pressure. This idea is a natural extension of the concept of pressure at residual volume initially promulgated by Kaefer et al.1 They recorded bladder