Female stress urinary incontinence is an ancient problem. Following the "hammock hypothesis" by DeLancey, which describes the pathophysiology of female stress incontinence (1), the tension-free vaginal tape (TVT) procedure for treatment of stress urinary incontinence in women was introduced in 1996 (2). The TVT procedure is a minimally invasive surgical method for treating female urinary incontinence that has gained widespread popularity. The procedure requires positioning of a vaginal tape precisely underneath the mid-urethra with no tension, to restore urethral support.

With techniques used previously, most studies report a high cure rate and long-term durability (3). Surgeons who consider adopting the TVT procedure for their patients need to give attention not only to the efficacy of the procedure but also to the potential complications and untoward effects which may impact upon patient satisfaction and quality of life. Voiding dysfunction is a well recognized complication when using suburethral sling procedures (4, 5). It has been reported that subjective and objective voiding patterns could change after the TVT procedure (6). Voiding dysfunction has been estimated to occur at a rate of 1.5-20% after the TVT procedure (7, 8). Therefore, it is of interest to understand the reason why significant postoperative voiding dysfunctions follow the procedure and to determine whether those symptoms are predictable preoperatively. In this study, we evaluated comprehensive risk factors that may be predictive of postoperative voiding dysfunction, and factors having impact on patient satisfaction after the TVT procedure.

Mean operative time and the length of hospital stay were 28.4 min and 1.4 days, respectively. There was a significant decrease in peak flow rate by uroflowmetry preoperatively vs. postoperatively (30.1 vs. 23.5 mL/sec, p=0.0001) with a mean decline of 6.6 mL/sec. However, change in volume of residual urine was not significant (16.7 vs. 20.5 mL, p=0.271). Two hundred and sixty-one patients (91.6%) favored the procedure in answers to a global satisfaction questionnaire. There were 268 patients (94.0%) with an intention to recommend the surgery to others. Subjective and objective cure rates were 93.7% and 90.9%, respectively.

Voiding dysfunction developed in 29 (10.2%) of the 285 patients. Patient's peak flow rate only showed significant differences between the normal voiding group and voiding dysfunction group (preoperative peak urinary flow rate: 30.8 vs. 23.7 mL/sec, p=0.004, Table 2). When we generated an ROC curve for peak urinary flow rate, the area under the curve was 0.684; sensitivity and specificity were 22.3% and 55.2% at 20.9 mL/sec, and 33.6% and 34.5% at 23.9 mL/s, respectively (Fig. 1). When we compared the difference in patients' satisfaction rate between patients with preoperative peak flow rate lower and higher than 20 mL/sec according to this result, there was no statistical difference between them (data not shown). Also, there was no statistically significant difference between those with and without voiding dysfunction in terms of cure rates, patients' satisfaction and intention to recommend the surgery to others (Table 3). Postoperative peak urinary flow rate was less than 12 mL/sec in 23 patients, less than 10 mL/sec in 17 patients, and less than 8 mL/sec in six patients. The mean decline in peak urinary flow rate from their preoperative value was 13.4 mL/sec for patients with less than 12 mL/sec, 12.7 mL/sec for patients with less than 10 mL/sec, and 12.9 mL/sec for patients with less than 8 mL/sec. When we stratified all patients by these 3 postoperative peak flow rate values, significantly lower level of global satisfaction was noted from patients with a peak urinary flow rate less than 8-10 mL/sec, though the statistics were not significant for patients passing 12 mL/sec (Table 4). The mean preoperative peak urinary flow rates were 21.6 and 20.3 mL/sec in patients with less than 10 and 8 mL/sec postoperatively. In patients with a preoperative peak urinary flow rate less than 20 mL/sec, of less than 10 mL/sec than more than 20 mL/sec (Table 5).

The TVT procedure has rapidly become a widely performed operation in Korea. It offers advantages over conventional repairs: it is quick and can be done under local anesthesia. Though the procedure is well known as an effective approach with a high long-term cure rate, Boustead (12) indicated that 1.5-20% of patients can develop postoperative voiding dysfunction. The question is whether these postoperative voiding dysfunctions are predictable preoperatively, whether patients' satisfaction is related with voiding dysfunction, and whether there are pre- or postoperative risk factors predictive of patients' satisfaction. We previously reported that peak urinary flow rate is an independent prognostic factor for immediate postoperative urinary retention after the TVT procedure and its significant influence on patient satisfaction (13).

Prevalence and predictors of voiding dysfunction after various sling procedures have been identified but unfortunately vary among different institutions. The most likely reason for this difference is the lack of standard definitions of voiding dysfunction. For instance, Groutz et al. (14) defined it as a maximum flow rate less than 12 mL/sec, or residual urine volume greater than 100 mL. Stanton et al. (15) defined voiding difficulty as a peak flow rate less than 15 mL/sec (if at least 200 mL had been voided), or greater than 200 mL of residual urine on two or more readings. Lose et al. (9) defined impaired bladder emptying as a peak flow rate less than 15 mL/sec for patients younger than 60 yr and less than 10 mL/sec for patients 60 yr or older (at a voided volume greater than 150 mL). In terms of the TVT procedure, Wang et al. (16) defined normal voiding as a postvoid residual urine <100 mL, frequency of six of fewer voids per day and two or fewer per night, and a urinary stream considered normal by the patient.

The definition of voiding dysfunction in the current study is a peak urinary flow rate less than 10 mL/sec (voided volume greater than 100 mL) as straining voiding, or residual urine volume greater than 30% of the maximum bladder capacity as poor emptying on two or more readings. Based on our definition, 29 (10.2%) patients were included in the voiding dysfunction group. Among the clinical factors, preoperative peak flow rate only showed significant differences between the normal voiding and voiding dysfunction groups (Table 2). When we generated an ROC curve for peak urinary flow rate, the area under the curve was 0.684; sensitivity and specificity were 22.3% and 55.2% at 20.9 mL/sec, and 33.6% and 34.5% at 23.9 mL/sec, respectively (Fig. 1). This means peak urinary flow rate can effectively estimate the risk of voiding dysfunction and predict postoperative urinary retention. Anti-incontinence surgeries cannot avoid inducing some degree of obstruction to the lower urinary tract. The TVT procedure is not much different in this regard, although this procedure is completely tension free. Sander et al. (6) reported the peak urinary flow rate decreased from a preoperative 29.4 mL/sec to postoperative 24.5 mL/sec (p=0.036). There was a significant decrease in the peak urinary flow rate preoperatively versus postoperatively (30.1 mL/sec; 23.5 mL/sec, respectively, p<0.001) with an average decline of 6.6 mL/sec in our study. From our results, the risk of developing voiding dysfunction can be effectively stratified by the average decline in peak urinary flow rates. The intriguing point is that voiding dysfunction itself did not have a significant impact on patient satisfaction in most patients. This means most patients are still satisfied with gaining continence at the expense of a decrease in flow rate and a 6.6 mL/sec decline in peak urinary flow rate is modest enough to endure for most of the patients. Likewise, the preoperative peak flow rate predictive of voiding dysfunction, 20 mL/sec in the current study, could not effectively predict patients' satisfaction after the surgery. Furthermore, we could not find any relevance between patients' satisfaction and preor postoperative risk factors in patients with normal voiding and even in patients with voiding dysfunction. However, when we stratified all patients into subgroups according to specific postoperative peak flow rates, if a patient already had a low peak urinary flow rate that was not able to buffer the inevitable decline, or the decline in peak urinary flow rate was severe enough to be less than 10 mL/sec, global satisfaction with the procedure was significantly compromised. This result signifies patients' satisfaction depends much more on postoperative peak flow rate itself than on voiding dysfunction. Though we could not find any significant correlation between preoperative peak flow rate and patients'satisfaction in this study, the descent of peak flow rate was more significant in patients with less than 10 and 8 mL/sec postoperatively and preoperative peak flow rate was already lower in them (about 20 mL/sec) comparing to the mean preoperative peak flow in all patients (about 30 mL/sec). In this context, this ostensibly "tension-free" procedure may actually only be "tension-tolerable" in a sense. In any situation where the tension is intolerable, patients' satisfaction on the gaining of continence can be overcome by the disappointing urinary flow rate as shown in this study. Therefore, all efforts decreasing tension should be taken in applying vaginal tape and particular attention should be given to patients with already low preoperative peak flow rate in terms of placement of vaginal tape and preoperative warning of potential voiding risk after the procedure.

Peak flow rate is the most important factor in predicting postoperative voiding dysfunction. Patient satisfaction on the highly curative TVT procedure is not significantly influenced by postoperative voiding dysfunction based on the current definition. However, the inevitable decline in peak urinary flow rates may compromise patient satisfaction with the procedure when their postoperative flow rate is less than 10 mL/sec.