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| REVIEW ARTICLE |
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| Year : 2020 | Volume
: 31
| Issue : 6 | Page : 253-257 |
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Risk factors of morbidity and mortality after flexible ureteroscopic lithotripsy
Te-Yen Chuang1, Ming-Hong Kao1, Po-Cheng Chen1, Chung-Cheng Wang2
1 Department of Urology, College of Medicine, En Chu Kong Hospital, National Taiwan University, New Taipei City, Taiwan
2 Department of Urology, College of Medicine, En Chu Kong Hospital, National Taiwan University, New Taipei City; Department of Biomedical Engineering, Chung Yuan Christian University, Chung-li, Taoyuan City, Taiwan
| Date of Submission | 11-Jun-2020 |
| Date of Decision | 31-Aug-2020 |
| Date of Acceptance | 08-Oct-2020 |
| Date of Web Publication | 26-Dec-2020 |
Correspondence Address:
Chung-Cheng Wang
Department of Urology, En Chu Kong Hospital, 399, Fuxing Road, Sanxia District, New Taipei City
Taiwan
 Source of Support: None, Conflict of Interest: None  | 3 |
DOI: 10.4103/UROS.UROS_85_20
The use of the flexible ureteroscope for treating renal and ureteral calculi has rapidly increased in the last decade. Although the use of the flexible ureteroscope by experienced surgeons has excellent outcomes and safety profiles, several studies have reported many surgical complications with its use. We conducted a narrative review of the published literature sourced from PubMed. We used a combination of three keywords: “ureteroscope,” “morbidity,” and “urolithiasis,” with or without the additional keywords of “infection,” “mortality,” “hematoma,” and “ureteral injury.” Infection, bleeding, and ureteral injury are the main complications. We analyzed the possible causes of morbidity and death after the use of a flexible ureteroscope. Finally, we propose recommendations to prevent these complications.
Keywords: Flexible ureteroscopy, morbidity, mortality, risk factor, urolithiasis
How to cite this article:
Chuang TY, Kao MH, Chen PC, Wang CC. Risk factors of morbidity and mortality after flexible ureteroscopic lithotripsy. Urol Sci 2020;31:253-7 |
| Introduction | |  |
With the advances in technology, flexible ureteroscopy (URS) has been considered as an alternative for managing proximal ureteral stones and renal stones. Major technological progress has been achieved for retrograde intrarenal surgery. The 2020 European Association of Urology Urolithiasis Guidelines suggest that technical improvements, including endoscope miniaturization, an improved deflection mechanism, enhanced optical quality and tools, and introduction of disposables, have led to increased use of URS for both renal and ureteral stones.[1] The 2016 American Urology Association guideline for the surgical management of stones notes that flexible URS has high overall success rates, with low morbidity and complications for the removal of proximal ureteral stones <2 cm in diameter. Treatment failure and retreatment rates are higher in the proximal ureter for semi-rigid URS than those in the flexible URS. Thus, clinicians performing URS for proximal ureteral stones should have a flexible URS available.[2]
Recent evidence suggests that URS in the hands of experienced surgeons has an excellent safety profile, with stone-free rates and treatment efficiency superior to shock wave lithotripsy for large ureteral and nonstaghorn renal stones.[3] However, with the increasing use of flexible URS, several studies have reported the possible morbidities and mortality during and after flexible URS. Identifying these risk factors is essential for endo-urologists performing flexible URS. In this review, we summarize the possible complications and risk factors of these complications and propose preventive methods to decrease the occurrence of these events.
| Risk Factors for Bleeding after Flexible Ureteroscopic Lithotripsy | | |
Bleeding, infection, and ureteral injury are three main complications after semi-rigid and flexible URS. In 2012, Bai et al. reported that 11 patients (0.4%) developed a subcapsular renal hematoma after semi-rigid URS using a holmium:Yttrium-aluminum-garnet (Ho:YAG) laser. Patients who developed a perirenal hematoma had larger stones, more severe hydronephrosis, longer operation duration (41 vs. 33 min, P < 0.001), and higher perfusion pressure for hydraulic irrigation (P < 0.001) than patients who did not develop a perirenal hematoma.[4] In 2013, Chiu et al. identified 4 (0.36%) of 1114 patients who were diagnosed with subcapsular hematoma after URS.[5] All four patients had the triad of loin pain, fever, and a significant hemoglobin drop necessitating a blood transfusion. Large obstructive proximal ureteral stones and thin renal cortex were risk factors of a postoperative perirenal hematoma.[5] In 2016, Kao and Wang retrospectively analyzed 45 patients undergoing flexible URS and found that 4 (8.9%) patients with lower body mass index, chronic kidney disease, and a thinner renal cortex had a higher risk of developing a perirenal hematoma.[6] They proposed that during flexible URS, high irrigation pressure to maintain adequate vision may be associated with postoperative bleeding.
Another report by Baş et al. showed that the incidence of bleeding after flexible URS was 25 (1.59%) among 1571 procedures.[7] Interestingly, five patients receiving anticoagulant treatment and six patients with bleeding diathesis had no bleeding complication. Turna et al. also found that patients with and without anticoagulation had similar hemorrhagic or thromboembolic adverse events.[8] Thus, flexible URS remains the only potential surgical alternative for renal stones in patients on anticoagulant therapy, which is a contraindication to other minimally invasive treatment options (e.g., percutaneous nephrolithotomy or extracorporeal shock wave lithotripsy).
| Risk Factors of Infection after Flexible Ureteroscopy Lithotripsy | | |
Postoperative infectious complications are the most common and serious complications for patients after flexible URS. According to past studies, postoperative urinary tract infection (UTI) was defined as a body temperature higher than 38°C in association with pyuria or bacteria (or both), without any other focal infection site. In addition, other diagnostic criteria included flank pain, costovertebral angle tenderness, radiological or ultrasound findings (nephritis, perirenal abscess, or hydronephrosis), and suspicious laboratory testing results such as high white blood cell counts and C-reactive protein.
Recently, a systematic review and meta-analysis based on 12,357 patients from 16 studies showed that female sex (odds ratio [OR] = 1.82, 95% confidence interval [CI]: 1.78–2.23), diabetes mellitus (OR = 1.40, 95% CI: 1.07–1.85), positive urine culture before operation (OR = 2.18, 95% CI: 1.34–3.57), operation duration (OR: 1.03, 95% CI: 1.01–1.04), and preoperative ureteric stent placement (OR = 1.91, 95% CI: 1.26–2.91) were risk factors for infection after semirigid URS or flexible URS.[9] Of these patients, 1660 in four retrospective studies underwent flexible URS only. Four studies have shown that in the multivariate analysis, the risk factors for symptomatic UTI were diabetes mellitus, preoperative serum CRP level, female sex, stone burden, operation duration, and preoperative UTI.
However, there were different findings from other study groups. In one retrospective study of 1571 procedures, only stone size, stone number, and presence of congenital renal abnormalities were factors affecting complications after flexible URS.[9] In addition, Ozgor et al. analyzed the risk factors for infectious complications in 463 patients undergoing flexible URS. Multivariate regression analysis showed that operation time >60 min, presence of a renal abnormality, and age <40 years were predictive factors for infection complications.[10] One retrospective study of 316 procedures revealed that previous ureteral stenting had no association with postoperative complications.[11] Among all risk factors, operation duration has been considered a “comprehensive factor” because many factors such as stone burden, stone location, renal structure, and surgeon experience may affect the operation duration.[9] Longer operation time means longer irrigation time, which may lead to more bacteria being flushed into the upper urinary tract and more severe infectious complications. Although there is no consensus on the upper threshold of operation duration, Moses et al. demonstrated that operative time >120 min results in higher unplanned returns to the hospital for infections (89.5% versus 32.6%, P < 0.001).[12]
| Risk Factors of Ureteral Injury after Flexible Ureteroscopy Lithotripsy | | |
Ureteral injuries in association with ureteral stricture were common complications after flexible URS. In 2013, Traxer and Thomas developed a novel grading system of ureteral wall injury.[13] The Traxer ureteral injury scale consists of the following: 0 for no ureteral lesion or only mucosal petechiae, 1 for mucosal erosion or mucosal flap without smooth muscle injury, 2 for an injury that involves the mucosa and smooth muscle but not the adventitia, 3 for full-thickness ureteral perforation, and 4 for ureteral avulsion with loss of ureteral continuity. High-grade injuries (2–4 on the scale) had significantly more ureteral strictures than low-grade injuries (0–1 on the scale).
In a prospective study, investigating the association between injuries caused by the use of a ureteral access sheath (UAS) and the formation of ureteral strictures, the application of the Traxer scale indicated that 46 (12.5%) patients had high-grade ureteral injuries and persistent postoperative hydronephrosis. These injuries, due to ureteral strictures, were not associated with a short stent duration (P = 0.11) or older age (P = 0.17).[14] Thus, a long stent duration of more than 3 months is not suggested as a feature indicative of severe ureteral injury.
The ureteral avulsion is the most devastating complication after flexible URS. A search of the Manufacturer and User Facility Device Experience database revealed some potentially novel mechanisms for this rare complication. Surgeons should be aware of dangerous situations, including locked deflection of a flexible URS, bunching of the distal bending rubber in a flexible URS, scabbard avulsion, and stone basketing.[15]
| Risk Factors of Mortality after Flexible Ureteroscopic Lithotripsy | | |
In 2011, Watson et al. reported one death due to urosepsis after bilateral semi-rigid URS for bilateral ureteral stones.[16] In 2016, Kao and Wang reported one (2.2%) death in a series of 45 patients who underwent initial flexible URS. A 67-year-old woman had underlying diabetes mellitus, hypertension, and chronic stage V kidney disease. She did not stop aspirin before flexible URS, and she underwent an emergency nephrectomy for a massive, progressively increasing hematoma due to unstable hemodynamic conditions after flexible URS for the removal of one 2.0 cm renal stone in her left kidney. She died 2 weeks after the nephrectomy due to urosepsis and multiple organ failure despite vigorous resuscitation.[6] In 2016, Cindolo et al. disclosed that six patients died after RIRS in which the causes of mortality were urosepsis in four patients, anesthesia in one patient, and a hemorrhagic complication in one patient.[17] To prevent future complications, they recommended some best practices including the following: (1) operate only on patients with sterile urine, (2) always place a UAS, (3) always irrigate with caution and check the continuous fluid outflow, (4) do not exceed an operative time of 120 min (60 min for children), and (5) carefully monitor patients in the early postoperative phase. They found that physicians were occasionally tempted to overdo for their patients, sometimes skipping safety rules with an inevitable increase in risks.
| How to Prevent Complications During Flexible Ureteroscopic Lithotripsy | | |
A comprehensive preoperative evaluation and planning are necessary to reduce postoperative complications. Physicians should explain the benefits and risks of flexible URS in detail to the patients and their families before the operation. For patients with a high risk of morbidity or mortality, prophylactic broad-spectrum antibiotics, intravenous fluids, good serum glucose control, upper urinary tract diversion (e.g., nephrostomy drainage), and limited operation time should be taken into consideration. During the operation, if any unstable hemodynamic changes are noted, the operation should be stopped immediately. Depending on the patient's clinical condition, the intensive care unit would be appropriate for critically unstable patients.
The surgical principles and standard operative procedures should be obeyed. Flexible URS can be performed under general anesthesia or spinal anesthesia. All procedures must be monitored with intraoperative fluoroscopy. Whether patients routinely underwent ureteral stent placement 7–14 days before flexible URS depends on the surgeon's experience. Patients were placed in the lithotomy position. Diagnostic semi-rigid URS was performed first. One or two hydrophilic safety guide wires were placed into the upper ureteral tract. A 12–16 Fr UAS was inserted into the ureteral orifice with the aid of fluoroscopy and cystoscopy. Next, the flexible URS was inserted with the aid of a continuous normal saline pumping system, with a pumping pressure of <200 cmH2O. If the video images were clear, the pumping pressure could be decreased depending on the surgeon's judgment. The stone was disintegrated using a Ho:YAG laser coupled to a 200 μm laser fiber. Different power and pulse settings can be adjusted to achieve quick stone fragmentation. At the end of the procedure, the ureter is inspected for possible lesions ureteroscopically and fluoroscopically, with the administration of contrast media. A double J ureteral catheter is inserted for 1 week to 3 months, depending on the grade of ureteral injury and stone burden.
A UAS is suggested to be used in all patients undergoing flexible URS. The common reasons for using a UAS are to facilitate multiple entries of a flexible URS into the upper urinary tract, to lower the intrapelvic pressure, to protect the ureteroscope, and to protect the ureter when extracting stone fragments.[18] High intrarenal pressure can result in forcing bacteria in the urinary tract into the bloodstream, which may cause systemic infection. Traxer et al. investigated the differences in treatment outcomes and complications for the removal of renal stones by flexible URS, either with or without the use of a UAS.[19] They demonstrated a significant decrease in infection-related complications when a UAS was used, with a decrease of 28.6% for fever, 18.6% for UTI, and 4.3% for sepsis versus 39.1% for fever, 23.9% for UTI, and 15.2% for sepsis in the non-UAS group.
The benefits of using a UAS have been demonstrated by several in vitro studies. Using a cadaver model, Rehman et al. found that the 12F or 14F access sheath was provided for maximum flow of the irrigant with an irrigation pressure of 200 cmH2O while maintaining a low intrarenal pelvic pressure of <20 cmH2O.[20] In addition, the length of the UAS is an important factor in reducing the intrarenal pressure. When the tip of the UAS and the ureteroscope are in proximity to one another, high inflow and outflow and low pressure can be achieved. Using an in vitro anatomic model into which a pressure transducer was incorporated, Ng et al. showed that a ureteral access catheter placed inside or alongside the UAS provides the high flow rates without a rise in the intrarenal pressure.[21] Recently, to prove this hypothesis, Zhu et al. developed a novel suctioning UAS and compared it with traditional UAS. Suctioning UAS had a lower incidence of fever (5.5% vs. 13.9%; P = 0.009) and urosepsis (1.8% vs. 6.7%; P = 0.03).[22] Furthermore, Deng et al. designed a patented intelligent system to facilitate flexible URS that included an irrigating and suctioning platform and a UAS with a pressure-sensitive tip.[23] This design enabled precise regulation of the infusion flow and control of the vacuum suctioning by computerized real-time recording and monitoring of renal pelvis pressure. The significant benefit was the fact that the actual renal pelvis pressure of all 90 patients could be controlled to <20 mmHg, with clear operative visualization. Thus, no Clavien Dindo III-V complications were noted.
The quality of video images with flexible URS is another important but easily ignored factor for the prevention of complications. In the case of unclear vision during an operation, the pressure of the endoscopic irrigation pump or manual pumping system can be increased for better vision. Such an increase can cause high intrarenal pressure of over 40 cmH2O and may result in pyelovenous or pyelolymphatic backflow.[24] An interesting in vitro comparison conducted by Talso et al. showed that the image quality of digital URS was rated better than that of fiber optic URS.[25] Another ex vivo assessment and cost analysis by Hennessey et al. showed that, compared to reusable, flexible URS, single-use disposable, digital flexible URS might provide cost savings for hospitals and better image quality for physicians.[26] The image quality of reusable, flexible URS instruments gradually decreases over time and with the number of repair episodes. Thus, single-use disposable URS may be a better choice for preventing complications and be a more cost-effective option in the future.
Recently, Komeya et al. developed a nomogram to predict perioperative complications after flexible URS using five independent predictors. These predictors included age, female sex, stone volume, Hounsfield units, and narrow ureter diameter.[27] A narrow ureter was considered when there was an insertion of UAS only to the ureter, but no renal pelvis. This model could be used to alert physicians to patients who are at high risk of complications. This knowledge would allow the physician to take extra care with preoperative preparation and to be extra vigilant with these patients.
Finally, practice makes perfect. It is estimated that a surgeon should perform 50 or more flexible URS procedures to achieve surgical competence.[28] Simulators such as virtual reality, cadaveric, and artificial models and animal models are widely and effectively used to master the first steps of the learning curve quickly. Recently, the K-Box (Porgès-Coloplast, Humlebæk Denmark), a new simulation model for flexible URS, has been proven a valid, easy-to-use training model for initiating new endoscopists to flexible URS.[29] In addition, Avicenna Roboflex (Glendale Heights, Illinois, USA), a new robotic system, has been introduced for assisting with flexible URS. It has shown good outcomes for stone-free rate and safety, with significant improvements in ergonomics.[30] Thus, considering ethical and safety standards, simulators of flexible URS should be used by every beginner.
| Conclusion | | |
Flexible URS and its associated accessories have rapidly evolved in the last two decades. Flexible URS has become a viable alternative to shock wave lithotripsy or percutaneous nephrolithotomy. With the rapidly increasing use of flexible URS, several risk factors for complications such as bleeding, infection, and ureteral injury have been identified. The development of flexible URS skills in a simulator, comprehensive patient evaluation, and preoperative planning and preparation, following the standard operative safety procedures, and closely monitoring the patient during and after flexible URS are the key recommendations for flexible URS.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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