A “normal” postvoid residual (PVR) volume is generally defined as 200 mL or less. This value is based on consensus recommendations from the United States Department of Health and Human Services Agency for Health Care Policy and Research (AHCPR), which were published in 1992.1 According to these recommendations, a PVR volume less than 50 mL is considered indicative of adequate bladder emptying, and a PVR volume greater than 200 mL is considered indicative of inadequate emptying.1 There is minimal evidenced-based data on which these values are based. Additionally, there are no recommendations regarding the significance of PVR volumes between 50 and 200 mL.
Because there are limited data on which to base an objectively “normal” PVR volume in asymptomatic perimenopausal and postmenopausal women, there is a need for a reference range of PVR volumes to determine normal bladder emptying function in this population. Establishing “normal” PVR volumes would be important in extrapolating appropriate PVR volume ranges for patients immediately after anti-incontinence or prolapse surgeries to potentially determine criteria for retention and/or interventions such as bladder drainage. The specific aim of this study was to estimate the mean PVR volume in women without significant lower urinary tract or pelvic organ prolapse symptoms to establish these reference values.
MATERIALS AND METHODS
After obtaining approval from Walter Reed Army Medical Center Institutional Review Board, a prospective, descriptive study was initiated. From February 10, 2005, to March 15, 2006, perimenopausal and postmenopausal women aged 45 years or older presenting to the Gynecology Clinic at Walter Reed Army Medical Center for a well-woman encounter were offered study participation. Participants were predominantly recruited from well-women clinics, and nurse practitioner clinics, in particular, were targeted because of their preponderance of asymptomatic patients. After obtaining informed consent, demographic data, medical, surgical, and medication history, menopausal status, and past obstetric and gynecologic history were obtained by using a standard medical history questionnaire. A targeted history of urinary habits and incontinence was used to screen subjects for inclusion. Women were excluded if they presented with pelvic floor complaints, including symptomatic pelvic organ prolapse, frequent episodes of urinary incontinence, or symptoms of urinary retention, but women with infrequent urinary incontinence episodes (less than twice per week) and those who did not wear protective undergarment liners were considered eligible for participation. The decision to include these subjects was based on the high prevalence of infrequent urinary incontinence episodes in women of this age range and on a study by Diokno et al,2 which demonstrated no significant difference in PVR volumes in patients with urinary incontinence compared with continent women. Women with fewer than 10 voids per day and/or two or fewer voids per night were included; those with greater voiding frequencies (day or night) were excluded. The criteria for daytime and nighttime voiding frequency was based on a study of voiding diaries in a diverse populations of women by Fitzgerald et al.3 The criteria chosen for daytime and nighttime voids in our study were within 2 standard deviations (SDs) of the norm according to the Fitzgerald et al report. Women using anticholinergic medications for overactive bladder symptoms were initially considered as potentially eligible but were subsequently excluded because of the potential effect of these medications on voiding function and residual volumes.
Women who had undergone a previous anti-incontinence and/or pelvic prolapse corrective surgical procedure were still eligible for inclusion as long as they did not have specific lower urinary tract symptoms of urinary frequency, urinary incontinence, or pelvic organ prolapse as described. Those with significant neurologic disease (multiple sclerosis, spinal cord injury, or other neuropathies) or noteworthy renal disease were also excluded from participation. Additionally, women with current symptomatology of urinary tract infection or those with more than two documented urinary tract infections within the preceding year were excluded.
Before the physical examination, patients were asked to void, and the voided volume was recorded. Within 10 minutes of voiding, a bladder ultrasonographic scan was performed with the BladderScan BVI 6100 (Diagnostic Ultrasound Corporation, Bothell, WA). This method of bladder volume assessment has been shown to be accurate within 15% of bladder volume measured by catheter within a range of actual bladder volume of 0–999 mL.4,5 Bladder ultrasonography was used to eliminate discomfort and the risk of urinary tract infection associated with transurethral catheterization. All scans were performed by two of the authors (A.G., M.P.S.). A minimum of three scans were performed on each woman; the average volume from these scans was used as the PVR volume data point.
A physical examination was performed after bladder ultrasonography to assess the extent of pelvic relaxation, if any, and the degree of vaginal atrophy. Pelvic organ relaxation was recorded according to the pelvic organ prolapse quantification system.6 Urogenital atrophy was assessed as “present” or “absent” based on vaginal rugation.
Descriptive statistics are reported. Comparison of mean PVR volumes between groups according to age, body mass index (BMI), prior surgery, use of hormonal therapy, and atrophy were performed by using simple linear regression for continuous variables (number of years menopausal, BMI) and t tests for dichotomous group comparisons. Comparisons of mean PVR volumes according to obstetric history were performed by using t tests or analysis of variance, as appropriate. Comparison of median PVR volumes categorized according to stage of pelvic organ prolapse was performed by using the Kruskal-Wallis test. Statistical analysis was performed with JMP 4.0.4 (SAS Institute, Cary, NC). P<.05 was considered significant.
To estimate the sample size for the overall study (establishing a mean PVR volume), two studies of asymptomatic women in the perimenopausal and postmenopausal age range were considered.2,7 Using the estimated standard deviations from these two studies, a sample size of 100 women would allow an estimation of PVR volume from ±12 to ±17 mL, with a 95% confidence interval. For potential comparisons between groups as described in the preceding paragraph, a sample size of 100 women would provide 80% power to detect differences of approximately 42–50 mL between groups using a two-sample t test at a 5% significance level. Based on this analysis, a sample of 100 women was to be enrolled.
Approximately 200 women were initially offered participation in the study. After review of history and symptoms, 116 women met inclusion criteria. Of these 116 women, 100 were initially enrolled. Four women were subsequently excluded because of use of anticholinergic medications for overactive bladder symptomatology, resulting in a total of 96 enrolled asymptomatic perimenopausal and postmenopausal women. The mean age was 60±11 years, with a range of 45–87 years. The median gravidity and parity of the patients were 3 and 2, respectively; the mean BMI was 28±7 kg/m2. Postmenopausal women accounted for 80% of the study group; 30% of patients had undergone hysterectomy. Antihypertensives were used by 30% of the women in the study. Only 13 women (14%) were using some form of hormonal therapy.
An anti-incontinence procedure had been performed in 7% of patients, consisting of pubovaginal sling in three women, midurethral sling (transvaginal tape) in two, and anterior colporrhaphy/Kelly plication in two women. Only 6% of the participants had a history of corrective surgery for pelvic organ prolapse, including anterior colporrhaphy in two women and anterior plus posterior colporrhaphy in four. The vast majority (92%) of women had at least some degree of asymptomatic pelvic organ prolapse. The median stage of pelvic prolapse was 1, with 65% of patients having less than stage 1 prolapse (Table 1). Using the pelvic organ prolapse quantification system, the average site of the leading edge was –1.3±1.6. The leading edge of prolapse involved the anterior compartment in 70% of subjects. Vaginal atrophy was present in 55% of participants.
The majority of patients (76%) reported no incontinence symptoms; the remainder had only infrequent symptoms of two incontinence episodes per week or fewer, as defined in the inclusion criteria. Most of the women reporting infrequent incontinence described symptoms consistent with stress urinary incontinence. The mean number of daytime voids was six; the mean number of nighttime voids was less than one.
The median PVR volume among all asymptomatic perimenopausal and postmenopausal women was 19 mL, with a range of 0–145 mL. The overall mean PVR volume was 24±29 mL. The majority of women (85%) had a PVR volume of less than 50 mL, and 95% of patients had a PVR volume of 100 mL or less. Of the 54 participants who had a minimum voided volume of 150 mL before the bladder scan, the average voided volume was 292±25 mL, and the average PVR volume as a percentage of voided volume was 13%, with a range of 0–40%. For those women with voided volume less than 150 mL, the average voided volume was 91±50 mL, and the average PVR volume as a percentage of voided volume was 9.9% (range 0–70%). The PVR volume was significantly higher (P<.001) in those patients who voided more than 150 mL (30.3±32.0 mL) than in those who voided less (8.4±10.9 mL).
Overall mean PVR volumes and comparisons between groups of women categorized according to several variables are presented in Table 2. Of the demographic factors analyzed, only patient age was associated with differences in PVR volumes; those aged 65 years or older had higher PVR volumes compared with women aged less than 65 years. The number of years postmenopausal correlated with increased PVR volume (r=0.21, P<.05), but when stratified according to less than 5 years compared with 5 or more years menopausal, mean PVR volumes were not different. Body mass index, whether analyzed as a continuous variable or when categorized according to BMI less than 30 or 30 or more, was not associated with differences in PVR volumes. History of hysterectomy or anti-incontinence surgery, use of hormone therapy, and presence or absence of vaginal atrophy were also not associated with differences in PVR volumes.
Median PVR volumes in women categorized according to type and stage of prolapse are demonstrated in Table 1. Regardless of the stage used as a “cutoff” value for analysis or whether analysis was performed to evaluate the effect of individual stage, the degree of pelvic organ prolapse was not associated with differences in median PVR volumes. Although women with any degree of prolapse had higher PVR volumes than those without prolapse, this difference was not significant.
Postvoid residual volumes categorized according to obstetric history were also analyzed; parity of the participants ranged from 0 to 8. For analysis of mean PVR volumes according to parity, analysis of variance was performed, revealing no significant difference among PVR volumes (P=.45). Parity was also condensed into various dichotomous categorizations, again revealing no differences among PVR volumes. When considering route of delivery, there was no difference in mean PVR volumes between those only having undergone cesarean delivery compared with those who only delivered vaginally (29±41 mL compared with 24±26 mL, respectively, P=.060).
This study analyzed PVR volumes solely in asymptomatic perimenopausal and postmenopausal women without significant pelvic floor complaints. Our findings indicate that the majority (85%) of women in this group adequately empty their bladder, according to AHCPR guidelines. Additionally, none of the women in our study would be considered to have inadequate bladder emptying, based on the AHCPR criteria of a PVR volume of more than 200 mL. Our data indicates that voiding function, as measured by PVR volume, is well-maintained in asymptomatic women in this age group.
Despite the wide acceptance of the ACHPR guidelines and their incorporation into practice, limited data are available to support these criteria as markers for adequate or inadequate voiding. Several studies researching various urogynecologic topics have included PVR volume values for elderly women. Most of these investigations included institutionalized women or women with symptoms, including urinary incontinence or overactive bladder; several included women with significant neurologic disease.8–14 Only six studies evaluated PVR volumes in asymptomatic women, three of which included young women with mean ages of 27–29 years (Fink RA, Elser DM, Fantl JA, Toppi KA. Catheterized post-void residual volumes in asymptomatic females [abstract]. Int Urogynecol J Pelvic Floor Dysfunct 1996;7:5).2,7,15–17 There are only three studies that considered asymptomatic older women. One investigation included 40 women with a mean age of 75 years, but all were institutionalized, and many had significant comorbidities.7 Another study included 69 noninstitutionalized women with a mean age of 69.4 years in whom PVR volumes were reported; this investigation primarily evaluated urodynamic characteristics of continent and incontinent community-dwelling men and women.2 In both of these studies, only PVR volume ranges were reported, not mean values. A recent study of women in multiple age categories included an analysis of 17 asymptomatic perimenopausal and postmenopausal women; this investigation addressed several aspects of the voiding process as a function of age, and PVR volumes were reported.17 There is consequently little data specifically addressing asymptomatic perimenopausal or postmenopausal women to provide evidence-based normative data on which to base practice guidelines for possible use in symptomatic women or in women undergoing therapy for pelvic floor complaints. However, women in this age range form the population that accounts for the majority of those who seek care for prolapse or incontinence symptoms, often leading to therapeutic intervention, including surgery. Thus, establishing normative values is critical; it certainly seems more appropriate to base criteria of adequate or inadequate emptying on normal function in women of the same age group.
Our finding that increased age was associated with higher PVR volumes is consistent with prior studies demonstrating increases in PVR volume with age.2,13 Other investigators, however, have not identified a correlation between age and increased PVR volume.14,17 Pfisterer et al17 demonstrated that aging was associated with a significantly decreased detrusor contraction strength and urine flow rate, but PVR volumes were not different among premenopausal, perimenopausal, and postmenopausal women, although, as described, only 17 perimenopausal and postmenopausal women were included. Although we identified higher PVR volumes in women over the age of 65 years, this is not likely clinically significant because the mean PVR volume in the elderly women was still only 36 mL.
Hormonal therapy, clinically apparent urogenital atrophy, and number of years in postmenopausal status were not associated with differences in mean PVR volumes. These results are consistent with an analysis of the Women’s Health Initiative data, which demonstrated that estrogen supplementation in menopausal women did not improve urinary incontinence or bladder function.18
Obstetric history had essentially no association with differences in mean PVR volumes. Much of the data regarding urinary dysfunction and route of delivery primarily address incontinence, although there are reports that include data concerning PVR volume and urinary retention in the immediate postpartum period.19–21 Although these studies investigated risk factors for urinary retention in the immediate postpartum period, there are no long-term data directly comparing PVR volumes between those undergoing vaginal delivery and those having cesarean delivery. Our results indicate that the type of delivery does not appear to affect the bladder’s ability to empty remote from delivery.
There are several potential concerns with this study. By design, the study excluded women with factors that could potentially affect PVR volumes, including neurologic diseases, symptomatic pelvic organ prolapse, or significant urinary incontinence and urgency or frequency symptoms. However, our intent was to consider asymptomatic women in an attempt to identify normal indices, based on limited data in asymptomatic women in this age range. We did include those women with infrequent incontinence in this study because urinary incontinence is quite prevalent in women of this age group.22–24 If any degree of incontinence, even infrequent, resulted in exclusion of a potential study participant, recruitment of women into the study would have been significantly hampered. Additionally, inclusion of women with infrequent incontinence would provide a study population more consistent with women encountered in actual practice, with the results more applicable to women in this age group presenting for health maintenance or gynecologic issues. The same reasoning applies to the inclusion of asymptomatic women who had undergone prior corrective surgery for incontinence and/or prolapse, provided they met current inclusion criteria.
Another concern may be that we also did not include every potential woman presenting for health maintenance at our clinic during the time period specified; the patients in certain clinics were offered participation as described in the Materials and Methods section. While most women who were offered participation and met criteria for inclusion did indeed enroll in the study, we cannot discount the potential effect of selection and participation bias. Additionally, race, ethnicity, and socioeconomic status were not consistently recorded, which precludes important analysis of the data according to these variables. Furthermore, particularly due to a narrower distribution of results in our study compared with the limited data used to estimate the sample size, a larger number of patients would be needed to truly establish normative values. Lastly, there is no consensus on standardizing the measurement of PVR volume with regard to voided volume. In our population, a minimum 150 mL voided volume was significantly associated with an increased mean PVR volume. This will need to be further considered in establishing normative data.
Our data from asymptomatic perimenopausal and postmenopausal women, as well as data from other studies, as previously cited, support the AHCPR recommendation that a PVR volume less than 50 mL is consistent with “adequate emptying”. However, mean PVR volumes reported were far less than 50 mL. With the majority of women having a PVR volume of less than 50 mL, perhaps the 50 mL criterion is not accurate. Additionally, there is little data to support the concept of a PVR volume less than 200 mL being indicative of “inadequate emptying.” Considering that, in our study, 95% of the participants had a PVR volume of less than 100 mL, and that 2 SDs above the mean was 83 mL, perhaps a PVR volume of more than 100 mL might be a more appropriate indicator of “inadequate emptying,” based on PVR volume criteria in asymptomatic women in this age range. Finally, with the lack of any further “categorization” of patients with PVR volumes between 50 mL and 200 mL, and no studies addressing the clinical significance of a PVR volumes between 50 mL and 200 mL, it is difficult to determine if elevated PVR volumes in this range are clinically important, deserving of either further evaluation or therapeutic intervention. Based on limited data particularly addressing higher PVR volumes, further research is needed to determine an “abnormal” PVR volume requiring further clinical attention. It may indeed be found that the most important factor is clinical effect and not an arbitrarily defined volume. Further investigation addressing PVR volumes could be used to better define AHCPR recommendations and provide evidence-based guidelines for health care providers.
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