Outlet obstruction after sling surgery Vincent Tse and Lewis Chan Department of Urology, Concord Repatriation General Hospital, Sydney, Australia Urethral obstruction is not an uncommon complication after sling surgery for female stress urinary incontinence (SUI). This paper focuses on this complication in the context of the mid-urethral synthetic sling, which is now the predominate surgical option used by many surgeons in the treatment of female SUI. The epidemiology and risk factors predisposing to sling obstruction is reviewed, followed by a description of clinical features used in supporting the diagnosis. The use of urodynamics in conjunction with translabial ultrasound as a novel approach to assess the position of the sling and its relation to the urethra is

INTRODUCTION The mid-urethral synthetic sling (MUS) has become the most popular surgical treatment option for the management of urodynamic stress incontinence in women. Amongst the various types of MUS, the retropubic (e.g. tension-free vaginal tape) and transobturator routes are well established procedures, with data on the new minislings slowly emerging [1]. However, whether one chooses to employ an MUS or an autologous pubovaginal fascial sling at the bladder neck, complications such as urethral obstruction, de novo overactive bladder (OAB), haemorrhage, and visceral, vascular and nerve injuries may occur [2]. This paper will focus on the aetiology, risk factors, clinical features and diagnostic assessment of outlet obstruction post-sling, and conclude with a brief overview on treatment.

MECHANISM OF ACTION OF THE MUS The MUS concept is based on the integral theory by Petros and Ulmsten [3], whereby the sling mimics the action of the pubourethral ligament and thus enhances support at the mid-urethral level to prevent distraction of the urethral lumen during

24

What’s known on the subject? and What does the study add? This article provides a current update on the risk factors, clinical features, and diagnosis on obstruction after female stress incontinence surgery using the midurethral synthetic sling. Particular attention has been paid to identify the patient at risk for developing voiding difficulty post-sling surgery, as well as the utility of urodynamics and various imaging modalities, especially translabial ultrasound, in the diagnostic process.

explained. This is particularly important in the understanding of why the sling obstructs from an anatomical standpoint. The paper concludes with a brief overview on treatment options.

KEYWORDS

stress. However, some authors have suggested other mechanisms of action. Kelly and Zimmern [4] used micturating cystourethrography to show that there is urethral kinking during stress, thus proposing that the MUS may work by dynamic compression whereby the urethra is compressed at a time of raised abdominal pressure. Many studies have shown that in normal circumstances the MUS does not cause urodynamic obstruction during voiding [5].

technique is used to reduce the risk of obstruction, many surgeons leave a gap between the sling and the urethra at the end of the procedure to maximize the chance that the MUS is sited ‘tension-free’. Using this principle, Chung et al. [6] have shown that prolonged catheterization of more than 5 days, persistent de novo OAB and sling division for obstruction did not occur at 4-year follow-up. Murray et al. [7] have shown that patients with de novo urgency have a higher incidence of mid-urethral kinking and proximal urethral dilatation suggesting that this symptom is caused by obstruction The pubovaginal sling is associated with a higher risk of retention than the MUS [8], possibly because the former is more commonly used in patients with intrinsic sphincter deficiency and hence more tensioning is placed, or its more proximal position in the urethra may be associated with higher incidence of urgency.

RISK FACTORS FOR POST-SLING OBSTRUCTION EXCESSIVE URETHRAL COMPRESSION Based on the above working concepts, it is intuitively possible for obstruction to occur if there is excessive urethral compression by the MUS. Currently, there is no standardized method on how an MUS should be tensioned. One technique is to use the ‘cough test’ whereby patients having the procedure under intravenous sedation anaesthesia are asked to cough on the operating table after placement of the sling to allow the surgeon to adjust sling tension. However, there is no evidence to show that this technique is better than slings placed under general anaesthesia. Whatever

mid-urethral sling, obstruction, urodynamics

REDUCED PREOPERATIVE NON-INTUBATED PEAK FLOW RATES (Qmax) Wheeler et al. [9] showed that a preoperative Qmax > 30 mL/s was associated with the lowest risk of post-sling retention, whereas 77.3% who had Qmax < 15 mL/s failed the first voiding trial. This was

© BJU INTERNATIONAL

©

2 0 11 T H E A U T H O R S

2 0 11 B J U I N T E R N A T I O N A L | 1 0 8 , S U P P L E M E N T 2 , 2 4 – 2 8

OUTLET OBSTRUCTION AFTER SLING SURGERY

FIG. 1. Urodynamic tracing in a 39-year-old female after mid-urethral sling surgery showing a stable bladder, no urodynamic stress incontinence on coughing, but an outlet obstruction according to the Blaivas–Groutz nomogram with a protracted flow curve pattern, a Qmax of 17 mL/s and a detrusor pressure at Qmax of 37 cmH2O. UG

SD

00:00

11:49 24

20

19

19

pves 100 cmH2O

5

1

pabd 100 cmH2O

163

359

pdet 100 cmH2O

0

0

I. Vol 1000 ml

−1

Q 50 ml/s

−1

Qvol 1000 ml 1.00

2.00

3.00

4.00

5.00

6.00

7.00

supported by Cho et al. [10] using a Qmax of 15 mL/s as cut-off. PRESENCE OF DETRUSOR HYPOCONTRACTILITY Patients with features of detrusor hypocontractility on preoperative urodynamics may also be at risk of obstruction [11]. Dietz and Haylen [12] showed that, although the presence of voiding symptoms was associated with reduced non-intubated flow rates, the specific symptoms of straining to void and a sensation of incomplete emptying were not. These findings suggest that while voiding symptoms alone might be an unreliable indicator of the presence of pathological voiding, an abnormal non-intubated flow rate might indicate that pressure–flow studies should be considered before placing a sling to differentiate hypocontractility from dysfunctional voiding. Experienced surgeons know that the technique of sling tensioning may need to be modified in this group, although again there is no standardized method described.

8.00

9.00

10.00

11.00

urodynamic obstruction is not uncommonly reported after sling surgery [13]. However, patients with clinically significant post-sling obstruction often experience bothersome new-onset mixed storage and voiding symptoms [14]. Although de novo urgency is thought to be secondary to outlet obstruction, there is a difference in the reported incidence in the two entities. Storage symptoms such as frequency, urgency and nocturia have been associated with up to 20% of patients post-MUS [15]. In those patients who receives MUS only without concomitant prolapse repair, between 1% and 9% of patients may present with urinary retention, which according to the American Urological Association Guidelines for the Management of Stress Incontinence in Women is defined by catheter dependence of more than 28 days or the need to surgically intervene to resolve the retention [16]. If there is concomitant prolapse repair, the risk is up to 10% [17].

DIAGNOSTIC EVALUATION HISTORY AND PHYSICAL EXAMINATION

CLINICAL PRESENTATION A subjective decrease in flow with objective reduction in peak flow rates without

©

The temporal relationship of the sling procedure to symptom onset is paramount. It is useful to note the patient’s preoperative

urodynamic data such as initial flowmetry, post-void residual volume and detrusor contractility, as these parameters give an indication as to the patient’s preoperative detrusor function which, if abnormal, may contribute to an increased risk of post-sling voiding dysfunction [18]. Physical findings are often normal, but severe cases may reveal urethral hyper-suspension, retropubic angulation or a palpable band across the anterior vaginal wall at the mid-urethra. Retropubic angulation may also be appreciated on translabial ultrasound, voiding cysto-urethrogram and urethroscopy. Vaginal examination may reveal mesh extrusion or anterior vaginal wall prolapse [19]. URODYNAMIC FINDINGS (Fig. 1) Currently, the value of preoperative urodynamics in predicting post-sling voiding dysfunction has not been clearly established. Many authors have shown that initial flowmetry, voiding pressures and Valsalva voiding do not predict post-sling obstruction [20], while others found that the peak flow may be useful in predicting successful voiding trials post-MUS procedures [21,22]. Similarly there is no consensus on the urodynamic diagnosis of bladder outlet obstruction in women. Nitti et al. [22] used a combination of fluoroscopic evidence of obstruction with a sustained detrusor contraction to predict that women who are radiologically obstructed are associated with a lower Qmax and higher detrusor voiding pressure at Qmax than those who did not display fluoroscopic features of obstruction at bladder neck or urethra. In a study that used the criteria of detrusor pressure at Qmax of more than 30–40 cmH2O and a Qmax of less than 15 mL/s to define bladder outlet obstruction, 33% of patients with symptoms of voiding dysfunction did not meet these urodynamic criteria, although they probably had obstruction based on the temporal relationship of the sling to the occurrence of symptoms. Interestingly, the two groups benefited equally from urethrolysis; thus, urodynamics did not help predict the surgical outcome [23]. Although urodynamics may not be required in all patients being evaluated for urethral obstruction following sling surgery, it may provide important information about the patient’s lower urinary tract function, such as the presence of detrusor overactivity or underactivity. Furthermore, inconclusive

2 0 11 T H E A U T H O R S

BJU INTERNATIONAL

©

2 0 11 B J U I N T E R N A T I O N A L

25

TSE and CHAN

urodynamic findings should not be used to exclude patients from sling division.

FIG. 2. Translabial ultrasound images of the urethra of the patient illustrated in Fig. 1. At rest (left), the synthetic sling can be seen at mid-urethra as a hyperechoic area. During Valsalva (right), there is urethral kinking by the sling at mid-urethra.

With respect to urethral pressure profilometry, data abound in its use to confirm the diagnosis of intrinsic sphincter deficiency but there are very few data on its use in post-sling bladder dysfunction such as obstruction or de novo urgency. Gamble et al. [24] showed that de novo urgency and urge incontinence are associated with a higher maximum urethral closure pressure (MUCP) (odds ratio 0.83, P < 0.001). Another paper by Bump et al. [25] showed that, using urethral pressure profiles, inadequate pressure transmission ratios (less than 90%) to the urethra are often associated with sling failure, whilst higher transmission ratios close to 100% may raise MUCP but are associated with detrusor overactivity, suggesting that overactivity may be associated with an obstructing phenomenon.

Sling at mid-urethra

TRANSLABIAL ULTRASOUND Although fluoroscopy is traditionally used with urodynamics, translabial ultrasound can be a useful modality to image slings during a urodynamic study and to assess their location relative to the urethra [26]. Voiding dysfunction has been shown to be associated with sling migration or kinking of the urethra on ultrasound [27] (Fig. 2). The translabial approach provides a less distorted view of the urethra than the transvaginal approach. The latter requires the probe to be abutting the anterior vaginal wall during scanning and thus may distort the urethra. In the authors’ experience, kinking is observed only in urodynamically obstructed patients and is only one of the features which can contribute to the diagnosis. Other features which may coexist to support the diagnosis of obstruction include urodynamic changes, temporal relationship between sling surgery and onset of symptoms, changes on physical and cystoscopic examination, and kinking on voiding cysto-urethrogram. Voiding cysto-urethrography gives concomitant dynamic imaging with anatomical detail during voiding, whereby ultrasound can show anatomical detail with straining, with obstruction supported by concomitant urodynamics giving functional parameters. Another advantage of using ultrasound is its ability to reveal malpositioned slings. This feature is useful in assessing cases of persistence of stress incontinence after sling

26

placement (i.e. sling failure). It may be associated with sling migration or incorrect positioning at the time of surgery. CYSTO-URETHROSCOPY Cysto-urethroscopy may be used as an adjunct in the evaluation of obstruction post-sling procedures. It may reveal an angulated or kinked urethra. It also provides reassurance that no suture or mesh has eroded into the bladder or urethra which may present as storage symptoms [28]. It may be performed independently or at the time of surgical intervention for the obstruction depending on the clinical presentation of the patient and whether or not one suspects mesh erosion.

TREATMENT CONSERVATIVE Predominately storage rather than voiding symptoms may be managed by empirical anticholinergic therapy. Failing this, cysto-urethroscopy or urodynamics will be required to exclude obstruction or erosion. Little evidence or protocols exist to guide optimal timing of surgical intervention for

obstruction. Many high volume centres suggested that retention in the first 2 weeks be managed by clean intermittent selfcatheterization to see if voiding improves. Others would advocate earlier intervention with an aim to minimize patient discomfort, reduce the risk of structural damage to the detrusor from chronic obstruction and allow easier intraoperative sling identification before it is incorporated in fibrous tissue [29]. SURGERY If conservative treatment fails, sling loosening, sling incision or urethrolysis have been shown to achieve good outcomes. The surgical details of these procedures are not the focus of this paper but the general principle in sling loosening is to identify it through the surgical incision and pull caudad judiciously. Fascial pubovaginal sling may also be loosened by re-tying the knot suprapubically. Sling incision can then be done in the midline, often with a suburethral segment of sling excised. Success rates range from 84% to 93.5%. Recurrent stress incontinence may occur in up to 17%, with lower rates associated with longer intervals between sling placement and incision [30]. If sling incision fails,

© BJU INTERNATIONAL

©

2 0 11 T H E A U T H O R S

2 0 11 B J U I N T E R N A T I O N A L

OUTLET OBSTRUCTION AFTER SLING SURGERY

urethrolysis may be required. Three approaches have been described: transvaginal, suprameatal and retropubic, with each technique able to be supplemented with an interposition fat graft to reduce recurrent fibrosis. Success rates range between 65% and 93%, with recurrent incontinence occurring between 0 and 19% [31].

2

CONCLUSION

5

Although voiding dysfunction post-sling surgery can be managed satisfactorily in most cases, prevention is better than cure. Proper patient selection and meticulous surgical technique are vital to optimize patient outcome and minimize the risk of post-sling obstruction. Care should be taken to avoid excessive tension, especially when a synthetic sling is being used due to the additional risk of urethral erosion. Generally speaking, the sling should be ‘tension-free’ while the patient is in the dorsal lithotomy position intraoperatively so as to minimize possible urethral obstruction once the patient assumes the upright position. The tension-free state is also necessary to counteract any possible mesh shrinkage due to wound contraction from healing. A urodynamic study supplemented by fluoroscopy or translabial ultrasound may assist in confirming obstruction, but more importantly it may provide information about the patient’s lower urinary tract function, such as the presence of detrusor overactivity or underactivity, which may prognosticate treatment outcome. Inconclusive urodynamic findings should not be used to exclude patients from sling division or urethrolysis. Current studies are ongoing in trying to understand how slings obstruct and how to predict those at risk of obstruction.

3

4

6

7

8

9

10

11 CONFLICT OF INTEREST None declared.

REFERENCES 12 1

©

Kennelly MJ, Moore R, Nguyen JN, Lukban JC, Siegel S. Prospective evaluation of a single-incision sling for stress urinary incontinence. J Urol 2010; 184: 604-9

13

Daneshgari F, Kong W, Swartz M. Complications of mid urethral slings: important outcomes for future clinical trials. J Urol 2008; 180: 1890–7 Petros PE, Ulmsten U. An integral theory of female urinary incontinence. Acta Obstet Gynecol Scand 1990; 153 (Suppl.): 691–79 Kelly C, Zimmern P. Obstruction after tension-free vaginal tape. J Pelvic Surg 2002; 8: 169–71 Winters C. Urodynamics in the era of tension-free slings: defining the role. Curr Urol Rep 2004; 5: 343–7 Chung E, Tse V, Chan L. Mid-urethral synthetic slings in the treatment of urodynamic female stress urinary incontinence without concomitant pelvic prolapse repair: 4-year health-related quality of life outcomes. BJU Int 2009; 105: 514–7 Murray S, Haverkorn R, Koch Y, Lemack G, Zimmern P. Urethral distortion after placement of midurethral sling. J Urol 2011; 185: 1321–6 Dmochowski RR, Blaivas JM, Gormley EA et al. Female Stress Urinary Incontinence Update Panel of the American Urological Association Education and Research, Inc, Whetter LE. Update of AUA guideline on the surgical management of female stress urinary incontinence. J Urol 2010; 183: 1906– 14 Wheeler TL 2nd, Richter HE, Greer WJ, Bowling CB, Redden DT, Varner RE. Predictors of success with postoperative voiding trials after a mid urethral sling procedure. J Urol 2008; 179: 600–4 Cho ST, Song HC, Song HJ, Lee YG, Kim KK. Predictors of postoperative voiding dysfunction following transobsturator sling procedures in patients with stress urinary incontinence. Int Neurourol J 2010; 14: 26–33 Padmanabhan P, Nitti V. Voiding dysfunction after female antiincontinence surgery. In Badlani H, Davila GW, Michel MC, Rosette JJMCH eds, Continence: Current Concepts and Treatment Strategies. London: Springer, 1998: 493–508 Dietz HP, Haylen BT. Symptoms of voiding dysfunction: what do they really mean? Int Urogynecol J Pelvic Floor Dysfunct 2005; 15: 52–5 Lukacz ES, Luber KM, Nager CW. The effects of the tension-free vaginal tape

14

15

16

17

18

19

20

21

22

23

24

on voiding function: a prospective evaluation. Int Urogynecol J Pelvic Floor Dysfunct 2004; 15: 32–8 Lemack G. Urodynamic assessment of bladder outlet obstruction in women. Nature Clin Pract Urol 2006; 3: 3844 Amundsen CL, Guralnick ML, Webster GD. Variations in strategy for the treatment of urethral obstruction after a pubovaginal sling procedure. J Urol 2000; 164: 434-7 Miller EA, Webster GD. Postoperative complications of sling surgery. In Vasavada SP, Appell RA, Sand PK, Raz S eds, Female Urology, Urogynecology, and Voiding Dysfunction. New York: Taylor and Francis, 2005: 447–55 Walters MD, Karram MM. Sling procedures for stress urinary incontinence. In Walters MD, Karram MM eds, Urogynecology and Reconstructive Pelvic Surgery. Philadelphia: Mosby-Elsevier, 2007: 196–212 Hong B, Park S, Kim HS, Choo MS. Factors predictive of urinary retention after a tension-free vaginal tape procedure for female stress urinary incontinence. J Urol 2003; 170: 852– 6 Nitti VW, Fleischman N. Voiding dysfunction and urinary retention. In Walters MD, Karram MM eds, Urogynecology and Reconstructive Pelvic Surgery. Philadelphia: Mosby-Elsevier, 2007: 390–401 Lemack GE, Krauss S, Litman H et al. Normal preoperative urodynamic testing does not predict voiding dysfunction after Burch colposuspension versus pubovaginal sling. J Urol 2008; 180: 2076–80 Wheeler TL 2nd, Richter HE, Greer WJ, Bowling CB, Redden DT, Varner RE. Predictors of success with postoperative voiding trials after a mid urethral sling procedure. J Urol 2008; 179: 600– 4 Nitti VW, Tu LM, Gitlin J. Diagnosing bladder outlet obstruction in women. J Urol 1999; 161: 1535–40 Cross CA, Cespedes RD, English, SF, McGuire EJ. Transvaginal urethrolysis for urethral obstruction after antiincontinence surgery. J Urol 1998; 159: 1199–201 Gamble T, Botros S, Beaumont J et al. Predictors of persistent detrusor

2 0 11 T H E A U T H O R S

BJU INTERNATIONAL

©

2 0 11 B J U I N T E R N A T I O N A L

27

TSE and CHAN

overactivity after transvaginal sling procedures. Am J Obst Gyn 2008; 199: 696.e1–7 25 Bump R, Fantl A, Hurt GW. Dynamic urethral pressure profilometry pressure transmission ratio determinations after continence surgery: understanding the mechanism of success, failure, and complications. Obstet Gynecol 1988; 72: 870–4 26 Chan L. Ultrasound imaging for female urodynamics – technique, feasibility and patient acceptance. J Urol 2009; 181: 600 27 Chan L. Ultrasound imaging of transobturator male and female slings:

28

is there a common mechanism of action? J Urol 2011; 185: 538 28 Powers K, Lazarou G, Greston WM. Delayed urethral erosion after tensionfree vaginal tape. Int Urogynecol J Pelvic Floor Dysfunct 2006; 17: 422–5 29 Karram M, Segal B, Vassallo S, Kleeman S. Complications and untoward effects of the tension free vaginal tape procedure. Obstet Gynecol 2003; 101: 929–32 30 Abouassaly R, Steinberg JR, Lemieux M et al. Complications of tension-free vaginal tape surgery: a multiinstitutional review. BJU Int 2004; 94: 110–3

31 Dmochowski R, Appell R, Karram M. Complications of incontinence and prolapse surgery: evaluation, intervention, and resolution – a review from both specialties. AUA Annual Meeting Course 27 PG, 2008 Correspondence: Vincent Tse, Concord Hospital – Urology, Suite 101, Concord Hospital Medical Centre, Hospital Rd, Concord, NSW 2139, Australia. e-mail: [email protected] Abbreviations: MUS, mid-urethral synthetic sling; OAB, overactive bladder; MUCP, maximum urethral closure pressure.

© BJU INTERNATIONAL

©

2 0 11 T H E A U T H O R S

2 0 11 B J U I N T E R N A T I O N A L