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Keywords:

  • bladder outlet obstruction;
  • benign prostatic hyperplasia;
  • stents

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Authors

Objective To assess the use of a thermo-expandable intraprostatic stent (Memokath®, Engineers and Doctors A/S, Copenhagen, Denmark) for bladder outlet obstruction in men unable to undergo transurethral resection of the prostate (TURP), assessing symptoms, complications and duration of stent life.

Patients and methods The Memokath stent is a coil of a nickel-titanium alloy which has ‘shape memory’, the lower end expanding when heated to 55 °C. Risks associated with inserting the stent with a flexible cystoscope under local anaesthesia are minimal. Men were selected who were either permanently or temporarily unfit for TURP. Indications included severe respiratory and cardiovascular disease. Exclusion criteria included bladder carcinoma, calculi or detrusor failure; in all, 211 men were fitted with 217 intraprostatic stents over 8 years.

Results There were 1511 TURPs during the study period; the mean age of men receiving a stent was 80.2 years, compared with 70.2 years for those undergoing TURP. The International Prostate Symptom Score decreased from a mean of 20.3 to 8.2 (P < 0.001) in the first 3 months after stent placement; there was virtually no change over 7 years. During the follow-up, 38% of men died with their stents in situ, 34% remain alive, 23% have had their stents removed for failure and 4% were removed as they were no longer required. There was a 13% migration rate and 16% repositioning rate. There were few side-effects (pain 3%, haematuria 3%, incontinence 6% and infection 6%). These frail men were more likely to die than have their stent fail.

Conclusion The Memokath intraprostatic stent is a valuable addition to the armamentarium of the urologist treating elderly or frail men with advanced bladder outlet obstruction and complements existing technologies.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Authors

Urological surgeons who treat elderly men for BOO caused by prostatic enlargement have to manage patients who ought to undergo TURP but whose comorbidity is such that the only options are a long-term catheter or the risks of surgery. Many of these patients will already have reached the stage of acute or chronic retention. There are alternative techniques for managing advanced obstruction but most rely on general or regional anaesthesia. Considering these patients, in 1993 we started using thermo-expandable metal prostate stents. The key attribute of these stents is that they can be placed and, if necessary, removed under topical local anaesthetic alone.

Most men faced with the prospect of life-long catheterization desire a better option. Even with modern anaesthetic techniques not all men are fit for TURP. In a study of the morbidity of TURP in those aged > 80 years, Brierly et al.[1] found an early complication rate of 41% and a late complication rate of a further 22%. Recent stroke, myocardial infarction and significant cardiac dysrhythmias, often combined with severe respiratory problems, or the need for anticoagulants, serve to compound the risks of age and frailty.

The first description of prostatic stenting involved a metallic spiral stent for temporary relief of obstruction [2]. In the cardiovascular system, metallic stents have been used for many years, and stents have been used throughout the entire length of the gastrointestinal tract. In the oesophagus they have alleviated symptoms in patients with carcinoma [3–5]. A Nitinol (nickel–titanium alloy) stent in the duodenum aided palliation of a high-grade tumour [6]. Relief of obstructive jaundice caused by unresectable malignancy has been reported with some success [7,8] and in the colon in cases of malignant colorectal obstruction the use of stents is gaining wider acceptance [9]. Within the urinary tract Kulkarni and Bellamy [10] were instrumental in exploring the role of thermo-expandable metallic stents in the obstructed ureter.

Stent characteristics will determine whether the urothelium will grow over it, so that it becomes ‘epithelialized’. This feature used to be considered a positive attribute, given that a buried stent would be less liable to encrustation and infection; they were therefore termed ‘permanent stents’. However, it was only rarely possible to get the whole length of the stent to epithelialize and then, if problems developed, removal was very difficult and could never realistically be contemplated under local anaesthesia. Non-epithelializing stents are made of inert materials and do not promote a urothelial reaction, so they do not become incorporated; they were formerly termed ‘temporary’.

The characteristics of an ideal stent include easy placement under local anaesthesia, minimal local side-effects, e.g. tissue hyperplasia or encrustation, and a low risk of migration; the stent must be removable if necessary and endoscopy through it should be feasible. Epithelializing stents include the Urolume Wallstent® (American Medical Systems, Minnetonka, MN) and the Intraprostatic stent® (ASI Inc. San Clemente, CA). Initial results were encouraging [11,12] but a longer-term follow-up showed that they were prone to epithelial in-growth, encrustation, migration, recurrent UTI and LUTS, e.g. dysuria and urgency [13–15]. Many needed removal, which required general anaesthesia [16], negating the advantage of being able to avoid anaesthesia for the patient.

Non-epithelializing stents, e.g. the Prostakath®, a rigid gold-plated spiral (Engineers and Doctors A/S, Copenhagen, Denmark), were designed to be easy to insert and manipulate if necessary. Initial results were encouraging [17] but longer term data indicated success in only a few patients [18]; half needed removing within the first year [19].

The Memokath® 028 intraprostatic stent (Engineers and Doctors) is shown in Fig. 1, and is made of a shape-memory alloy of nickel and titanium. Such an alloy ‘remembers’ its shape and will return to that shape after it has been deformed, if it is heated to a given temperature. The alloy exists in two distinct crystalline forms, martensite and austenite. The former will, after a ‘plastic deformation’ within certain limits, return to its original shape when heated, as a result of a specific type of phase-change known as martensitic transformation. The process is complex and the transition temperature depends on alloy mix, deformation and type and direction of applied stresses, i.e. the atomic structure of one crystalline lattice is floppy while that of the other is rigid. Orthopaedic implants (e.g. bone plates, rods, staples, etc.) profit from the profound inertness of this alloy, while guidewires take advantage of its super-elasticity feature in the austenitic configuration. Urological stents depend on the inertness and the shape-memory effect.

image

Figure 1. The Memokath® 028 prostate stent (a), and deployed from the sheath (b). The tip of the sheath has a short screw thread that holds the stent. When hot water is flushed through the sheath it exits from the slits just behind the screw thread, and the lower end of the stent expands off the sheath.

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The memorized shape of the stent is that of a tight coil opening into a funnel at one end. However, when unpacked it is a straight coil mounted on an introducing device. Only when it is correctly positioned in the prostate is it heated with water at 55 °C; this then effects the transformation to its memorized shape. When cooled using water at 10 °C, it becomes soft and pliable, and can be removed with relative ease under local urethral anaesthesia. The alloy is not magnetic (and will therefore not preclude the patient from MRI) and has excellent biocompatibility properties; its first use was described by Poulsen et al. in 1993 [20]. The present report describes our 8-year experience (1993–2001) in over 200 men and highlights the long-term outcome and complications encountered with the Memokath stent.

Patients and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Authors

The insertion of a Memokath stent is preceded by a moderate analgesic, e.g. rectal diclofenac, and an oral antibiotic; urethral anaesthesia is induced with 2% lignocaine gel. A flexible cystoscope is passed to the bladder to assess urethral patency and exclude the presence of bladder calculi and tumours. The flexible cystoscope is held at the bladder neck and a marker placed on the cystoscope sheath at the tip of the penis. The cystoscope is then withdrawn to just below the apex of the verumontanum and a further marker placed. The distance between the markers gives an indication of the length of stent required. Further local urethral anaesthetic is applied before passing a 26 F sound to the bladder to ensure that the stent (24 F) will pass with no hindrance. The stent, on its introducing sheath, is mounted onto the flexible cystoscope so that the tip of the cystoscope is clear of the stent by 2–3 mm. The cystoscope is advanced until the tip just enters the bladder. After warning the patient, 50 mL of hot water is flushed through the cystoscope; this expands the lower 4–6 mm into a cone shape (44 F) just proximal to the sphincter, which ‘locks’ the stent into position (Fig. 1b). The cystoscope is then gently withdrawn through the stent; the distal end is checked, and the cystoscope and sheath removed.

From April 1993, 211 men with significant BOO who were considered to be at high risk for surgical intervention or who had long-term catheters with adequate bladder function accepted the placement of an intraprostatic spiral stent. They included patients with severe ischaemic heart disease, recent myocardial infarction or cerebrovascular accident, chronic obstructive airways disease, those awaiting coronary artery bypass surgery, or who had dementia, and patients > 75 years who were reluctant to undergo surgery. Exclusion criteria for the stents were the presence of bladder tumours, bladder calculi and detrusor failure.

The patients were followed every 6 months after stent placement, assessing their IPSS and satisfaction scores. The stent position was checked using a portable ultrasonographic system.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Authors

In all, 217 Memokath stents were used in 211 men, all as a day-case or outpatient procedure, unless the patient was already in hospital. The stents were placed under direct cystoscopic vision using urethral local anaesthesia; general anaesthesia was not used. In several patients with dementia mild sedation was necessary. The mode (range) stent length used was 40 (30–70) mm.

Over the same period, 1511 TURPs were undertaken in our unit; therefore, 14% of interventions for prostatic BOO involved placing an intraprostatic stent. The age differences of each cohort of patients are shown in Fig. 2; the mean (range) age in the TURP and stent groups were 70.2 (37–91) and 80.2 (54–103) years, respectively, i.e. a decade difference. The youngest patient stented was just 54 years old; he had acute urinary retention during an episode of chronic rejection of a heart–lung transplant. A 62-year-old man, the next youngest, developed retention after pneumonectomy, an ileo-femoral bypass for critical lower limb ischaemia, and a cardiovascular accident while on anticoagulants; he had a successful TURP 15 months later.

image

Figure 2. A plot showing the comparative ages of men undergoing TURP (green) or stent insertion (red hash).

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The reasons for stent placement rather than TURP are listed in Table 1; the main reason was cardiovascular risk factors, but general frailty was also a common cause. A few men had a stent placed as a true temporary device, i.e. the stent was intended to be removed after a certain period, e.g. waiting for coronary artery bypass grafting. Comorbidity as assessed by ASA grade was available in 158 of the stented patients (Table 2); there was a clear difference between them and the 792 of 1511 patients undergoing TURP for whom ASA data was available.

Table 1.  Reasons why the patient was unfit for surgery (not mutually exclusive)
Reasonn (%)
Severe cardiorespiratory disease95 (44)
Frail117 (54)
Dementia25 (12)
Anticoagulants/clotting abnormalities26 (12)
Temporarily unfit (e.g. before angioplasty,  coronary artery bypass grafting)12 (6)
Other (e.g. after brachytherapy, BOO)11 (5)
Table 2.  ASA grades of 158 stented patients and 792 undergoing TURP
ASA Grade DescriptionStent, n (%)TURP, n (%)
1Healthy 0298 (38)
2Mild systemic disease,  no functional limitation10 (6)405 (51)
3Severe systemic disease  with functional limitation74 (47)81 (10)
4Severe systemic disease,  constant threat to life74 (47)8 (1)
5Moribund 00

The IPSS was assessed in the men where possible; the mean (range, 95% CI) score before stent insertion (150 men) was 20.3 (5–32, 19.26–21.27). The scores before and after insertion were both confirmed as having a normal distribution (Kolmogorov–Smirnov test, P = 0.72 and 0.07, respectively). After stent insertion the IPSS decreased by 12.1 points (151 men) to 8.2 (0–25, 7.25–9.08), a significant difference (P < 0.001, paired t-test; the 95% CI for the difference of paired samples was 10.03–12.79). The ‘bother’ score (0–6) decreased by 59% from a mean of 4.1 to 1.7.

The IPSS after insertion changed little over time; Fig. 3 shows the IPSS before and after stent insertion and then annually for 7 years (all patients stented during 1993 had died by 2001). Table 3 shows the change in IPSS by indication for intervention (symptoms, acute or chronic retention) cancer and dementia; these indications are not mutually exclusive. Patients treated for acute retention were asked to estimate their symptoms before the episode of retention.

image

Figure 3. The IPSS before and after stent insertion, and over time; the numbers of men in each group is shown.

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Table 3.  The change in IPSS by indication for intervention
StateNo.IPSS
BeforeAfterDecrease (Δ%)
Severe symptoms10520.68.711.9 (58)
Acute retention7719.67.911.7 (60)
Chronic retention3019.25.613.3 (71)
Cancer1723.49.513.9 (59)
Dementia2519.39.79.6 (50)

Of the 217 stents placed, 52 (24%) were removed, but eight of these men (4%) had their stents removed electively as they were no longer necessary (e.g. patients rendered fit again after coronary artery bypass grafting, so that TURP could once again be considered). Stents were removed for many different reasons, from worsening symptoms to migration. Several men had their stents removed because their prostates outgrew their stent; in these cases the middle lobe or bladder neck was then able to occlude the proximal aperture of the stent. In those men who had benefited from their intraprostatic stent, a longer stent was inserted (six patients).

Patients with high comorbidity have a risk of dying in the short term. Placing a foreign body in the urinary tract also has a finite lifetime before failure. Although there were several patients whose stents remained in place after >6 years it is important when considering the merits and demerits of a given treatment to know whether the stent is likely to fail within the patient's expected lifespan. Figure 4 shows a Kaplan–Meier survival curve for those patients who either died or whose stents failed. The implication is that stents may fail but the patient is more likely to die first.

image

Figure 4. Kaplan–Meier survival analysis of the stents in men living with intraprostatic stents (green open circles), compared with those men who died with their stents in situ (red closed circles; sample size 214).

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When evaluating management for BOO it is routine to assess maximum and average flow rates before and after treatment. Although this was begun in the present series it soon became clear that with men having this degree of comorbidity the logistics of obtaining flow rates were challenging for patients and staff alike. Furthermore, there seemed to be little correlation between the values that were obtained and the patients' symptom scores. Because these stents are readily visible using ultrasonography, in practice it is more helpful to assess the patient using a portable scanner to establish that the stent remains in a satisfactory position, that there is no large residual volume and obtain an IPSS. The relief of symptoms is more important to the patient than the velocity of his urinary stream.

There was a 10% rate of early acute urinary retention after insertion (Table 4); a few days of suprapubic catheterization resolved this in almost all the patients. Some of these men probably had transient difficulty with sphincter relaxation as a result of stent insertion, but it might also be a result of transient oedema or sphincter spasm induced by the insertion.

Table 4.  Complications
Complicationn (%)
Migration29 (13)
Retention (after procedure)21 (10)
Incontinence14 (6)
Infection13 (6)
Pain7 (3)
Bleeding6 (3)
Stone formation5 (2)
Occlusion3 (1)

Stents migrated in 29 (13%) of the men; migration did not always necessitate stent removal, as methods of in situ repositioning were developed. This was carried out on 33 occasions, again under local anaesthetic as a day-case or outpatient procedure.

UTI was a problem in only 13 men (6%), and significant stent encrustation or stone formation occurred in five patients (2%), one of whom needed a general anaesthetic for stent/stone removal. Many stents, when examined after prolonged insertion, had a bronze appearance (when new they are dull grey). When the removed stents were allowed to dry the bronze coating tended to come away from the stent as a fine powder; its composition has not been established. Significant epithelial in-growth occurred in four patients; later stents were manufactured with a much tighter coil to minimize this risk and it only became a problem in one patient who had been fitted with an ‘old’ type of stent.

Impaired continence was a problem in 14 patients (6%), in many cases probably as a result of unrestrained detrusor instability after prolonged obstruction; it often responded to anticholinergics. In two cases the lower end of the coil became distracted and directly impaired sphincter function, so that replacement of the stent was necessary in these men.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Authors

The high proportion of stents inserted by our unit (14%) is a reflection of our interest in the technique, which has led to referrals from elsewhere. The insertion of this stent is relatively easy and normally undertaken as an outpatient procedure under local urethral anaesthesia. Placing the stent is no more uncomfortable than flexible cystoscopy until the instillation of hot water into the urethra and bladder, which causes discomfort for 4–5 s. However, when men are forewarned of the ‘hot flush’ they tolerate it well; the whole procedure takes ≈20 min. Most men void immediately after the procedure and the outcome of stent placement, as judged by the ability to void (and often with a stream that the patient cannot believe), is immediately apparent.

Selecting patients for any procedure aims to ensure that the planned procedure is appropriate to the patient's condition and circumstances, so that there is the best possible chance of a satisfactory outcome. The men were chosen primarily for their willingness to have a surgical procedure but were at high surgical risk. This cohort of men obviously included many elderly men (mean age 80.2 years). As noted earlier, TURP can benefit patients aged > 80 years [1], but they have high morbidity from age alone. The comorbid disease states present were those of old age (as noted) and are not universal at this age but the prevalence is much greater.

Stents were placed in 25 (12%) patients with dementia, many of whom were deemed fit only for long-term catheterization but who soon demonstrated their ability to remove their catheters! Their symptom scores were estimated by their carers, who were mostly impressed that their charges instinctively knew when they had to find the toilet; others required regular toileting.

Seventeen patients with known prostatic carcinoma also had stents placed; most had extensive local disease causing obstruction. Tissue in-growth was not a problem in these cases. If patients need radiotherapy for prostatic cancer there should be uniform dosimetry to the gland, assuming opposing ports are used. Studies have shown that there is an 18% reduction in dose to the far side of a stent and 20% enhancement on the near side [21]. Using conventional multiport treatment protocols, this is not likely to cause any problems of uneven dosimetry.

Patient selection should not be based upon age and comorbidity alone. The failure rate of the stents is partly a result of possibly poor bladder function in these elderly men. Urodynamic tests in some men were used to assess detrusor activity before stent placement. In those with a urinary catheter, the bladder was filled with 500 mL of normal saline; if there was a sensory desire to void then it was considered that the bladder was suitable for this form of therapy. The number of stent failures has declined after using this simple protocol.

The complication rate with these stents is low at the present follow-up. Encrustation is rare, in-growth uncommon and migration relatively easy to rectify under local anaesthesia. The reason for the lack of encrustation on these stents is unknown. Possibly it is a result of the exceptional smoothness of the surface of the stent, the inert property of the alloy or the gentle massaging action of subtle movement within the prostatic urethra. Increasing prostate growth causing stent obstruction has been managed by replacement with a longer stent. No bladder stones have formed and two bladder tumours, presenting with haematuria, were diagnosed in patients with stent in situ. The stents allowed cystoscopic detection of these tumours but, once discovered, the management of these lesions required that the stents were removed to allow access with a resectoscope.

In our institution patients who undergo TURP have a mean hospital stay of 2.2 days; they are then followed by telephone interview 8–10 weeks afterward by a nurse practitioner. The total cost of TURP is ≈£1050 per patient and that of insertion of a prostatic stent ≈£1200. Because of our special interest in these stents, and their benefits and complications, we are undertaking long-term surveillance of the patients. The cost would be less if such protracted follow-up were simplified.

Long-term catheterization is sometimes considered as a simple and inexpensive option, but Booth et al.[22] showed that the cost of care for a patient with an indwelling catheter is at least £700/year. Most of the present stented patients who have had prolonged periods of catheterization remark on the freedom they feel in getting rid of the catheter. Furthermore, despite their comorbidity, several patients have been able to enjoy some sexual activity that would otherwise have been difficult.

The reduction in IPSS is immediate and similar to that after TURP; the present mean decrease was 12.1 points, and that in the National Prostatectomy study of 5361 patients in four health regions in the UK 12.9 points [23]. Furthermore, the stented patients were ≈10 years older than those undergoing TURP. Their bladders are unlikely to perform as well, as they are also older! The mean IPSS remained leqslant R: less-than-or-eq, slant10 during the follow-up. Patients sometimes report that they are aware of the presence of the stent for a 1–2 weeks; thereafter, they are usually unaware of it.

The Kaplan–Meier survival curve (Fig. 4) implies that a greater percentage of men die with their stents than outlive the usefulness of the stent, suggesting that generally the stents are well tolerated and have a reasonable life expectancy. They are less likely to produce severe side-effects compared with the benefit to the patient. They may be considered as ‘permanent’ stents in this elderly cohort of patients with significant comorbidity. Less than a quarter (23%) of stents were considered to have failed the patient, either through poor patient selection or where the stents caused unacceptable side-effects.

Over this study the important lessons were: (i) To slightly overestimate the length of the stent; a flexible cystoscope has a more direct course from bladder neck to sphincter than the stent when in situ. Also, a slightly overlong stent is not a major problem whereas one too short may obstruct; (ii) Try to clear any UTI before stenting (not always easy); (iii) Ensure that there is some detrusor function; (iv) Ensure that the patient and/or carer has an information sheet on what is being done and why. In particular they must appreciate that if they ever need a urinary catheter it should be inserted suprapubically (only a 12 F catheter will pass through the stent).

Three-quarters of patients stented can expect a satisfactory outcome. This is not as high as the satisfaction after TURP (of an audited sample of 800 patients in our unit, 92% declared that their outcome was as good as or better than their expectation). The difference is partly a result of having a foreign body within the prostatic urethra and partly caused by the age of the patient's bladder. However, as a safe option for the patient with high comorbidity, the thermo-expandable stent is a valuable addition to the therapeutic armoury.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Authors

The authors thank Mrs J Stone for her contribution to the data retrieval for this study. We also thank Mr R.P. Kulkarni for his advice and contribution of patients. Patient Information sheets are available from the Department of Urology, Ashford Hospital.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Authors

Authors

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Authors

M.J.A. Perry, BSc, FRCS, Specialist Registrar.

A.J. Roodhouse, RGN, BSc, Urology Nurse Practitioner.

A.B. Gidlow, RGN, RM, BSc, MSc, Urology Nurse Practitioner.

T.G. Spicer, BA, MBBS, DCH, General Practitioner.

B.W. Ellis, MB, FRCS, Consultant Urological Surgeon.

B.W. Ellis, Director of Surgery, Department of Urology, Ashford Hospital, London Road, Ashford, Middlesex. TW15 3AA, UK. e-mail: brian.ellis@dial.pipex.com