Death of the Safety Guidewire

Introduction

Guidewires were initially developed for endovascular application and were adopted for endoscopic use in urology in the 1980s. ¹ The safety guidewire has since represented a significant part of endourologic percutaneous and ureteroscopic procedures, serving to maintain access to the upper urinary tract throughout the procedure should primary access to the kidney be lost or ureteral perforation/transection occur. Regardless of the complication, the safety guidewire ensured the ability to place either a nephrostomy tube or a ureteral stent at the end of a percutaneous or ureteroscopic procedure.

Recent advances in endoscopic percutaneous nephrostomy with the routine establishment of a “through-and-through” flank incision to urethral meatus guidewire along with the availability of smaller flexible ureteroscopes and current iterations of ureteral access sheaths ² have changed this paradigm, reducing guidewire usage during percutaneous or ureteroscopic procedures to one or none, respectively. ^{3 –7} Herein, we trace the historical development of the safety guidewire concept, review recent advances in technologies that have obsoleted the safety guidewire, and evaluate recent data suggesting that continued use of a safety guidewire during percutaneous or ureteroscopic procedures may, in today's environment, be counterproductive.

History of the Safety Guidewire

Clayman and associates first described the use of a “safety” guidewire in 1983 when reporting the feasibility of balloon dilation of a nephrostomy tract in an era where dilation was traditionally performed with rigid dilators over the initially placed guidewire. ⁸ Repeated aggressive dilation with metal or fascial dilators over a guidewire, although necessary to accommodate the 24 French⁺ (F) rigid nephroscopes, was commonly associated with injury to the upper urinary tract; perforation rates of 4%, stricture rates of as much as 8%, and ureteral reimplantation requirement in 3% of cases were reported in large ureteroscopy series at the time. ^9,10 Not uncommonly, the guidewire would be kinked and, thus, rendered unusable, creating a difficult situation. Hence, the practice evolved of placing two guidewires into the collecting system and deeming one the “working” guidewire for passage of dilators and the other a “safety” guidewire to be used only if there was a problem during the procedure (e.g., loss of renal access, sheath placed short of the collecting system, etc.) and to place the nephrostomy tube at the end of the case. ⁸

Soon thereafter, in the first published manual on endourology in 1984, Clayman and colleagues formally outlined the appropriate use of a 0.035–0.038 inch Bentson or Newton wire for use as a safety guidewire; it was first inserted in a retrograde manner and, subsequently, left in place for nephroscopic retrieval to establish “through-and-through” access from the flank to the urethral meatus. The safety guidewire, which was left adjacent to the endoscope and sutured to the skin, was separate from the “working” guidewire over which the balloon catheter and Amplatz sheath were placed. The “working” guidewire would be subsequently removed after either the Amplatz sheath or the endoscope was positioned in the collecting system. Over the safety guidewire, a ureteral stent or nephroureteral catheter could easily be passed at the end of the procedure regardless of any injury to the pelvis or ureter. ^8,11

Over the next two decades, use of the safety guidewire was repeatedly validated in the endourologic literature both for percutaneous nephrolithotomy (PCNL) and ureteroscopy. Retrograde safety guidewire and catheter placement allowed for other benefits to PCNL aside from stent placement, such as preventing stones from falling into the ureter during PCNL procedures. ¹¹ The use of the safety guidewire in ureteroscopy dates to 1987, when Ekman and colleagues reported its deployment in patients undergoing ureteroscopic stone removal. They reported several distinct advantages to its use, such as straightening, stabilization, and ease of navigation through edematous portions of the ureter. ¹²

In 2001, Kumar and associates ¹³ also recommended use of the safety guidewire during therapeutic ureteroscopy. After both a “working” guidewire and safety guidewire were inserted through a dual-lumen catheter, the flexible ureteroscope was passed over the “working” guidewire. Removal of the “working” guidewire with the safety guidewire left in place allowed for instrumentation through the working channel of the ureteroscope. They did, however, not recommend use of the safety guidewire during diagnostic procedures, as the safety guidewire did have the potential to alter diagnostic findings especially in cases of lateralizing idiopathic hematuria. In addition, they noted that presence of the safety guidewire occasionally made introduction of the ureteroscope over the “working” guidewire more difficult. ¹³ However, considering the numerous advantages, placement of a safety guidewire for both PCNL and ureteroscopic procedure was considered standard of care according to the 2007 edition of Campbell-Walsh Urology. ¹⁴

Advancements in Cystoscopy and Ureteroscopy

Since the advent of the 12F rigid rod lens ureteroscope for accessing the distal ureter, ¹⁵ endoscopes in urology have undergone significant reduction in size and expansion of their functional capabilities. By the 1990's, using fiber optic lens technology, semirigid ureteroscopes had been reduced in size to 7.2F with two 2.1F instrument channels, as well as two inches of flexibility at the tip of the device; this allowed for ureteroscopic lithotripsy in both male and female patients extending to the renal pelvis and on occasions into the upper pole of the kidney. ¹⁶ Further reduction in size down to a 6.9F tip semirigid ureteroscope soon followed. ¹⁷ With these smaller endoscopes, as documented by Stoller and colleagues, there was no longer any need to routinely dilate the ureter, thereby precluding the potential for tearing the ureter that was associated with the use of balloon and sequential ureteral dilators. ^15,18

The first clinical report of flexible ureteroscopy was in 1964 by Marshall. ¹⁹ These early prototype flexible ureteroscopes had neither instrument channels nor a deflection mechanism; they could only be used for diagnostic purposes, most commonly during open procedure. ^20,21 Over the past 50 years, flexible ureteroscopes have advanced to the point that they can routinely access the proximal portion of the ureter, the renal pelvis, and the vast majority of calices in almost all patients. ²⁰ With deflection angles of 275° and the replacement of fiber optic with digital viewing technology, today's flexible ureteroscopes provide an astounding view of the interior of the ureter and collecting system along with single or dual working channels for therapeutic procedures. ^{15,20 –22} In addition, given their typical 7-10F size, their passage up the ureter no longer requires routine ureteral dilation. ²²

Overall, the reduction in ureteroscope (both rigid and flexible) size over the years has greatly reduced ureteroscopic complications. ^23,24 Indeed, in a series of 1000 ureteroscopies at the Mayo Clinic reported in 2006, the overall complication rate was 1.9% with a 0.2% rate of ureteral strictures, ²⁵ a more than threefold decrease from the 6.6% complication rate reported from the same institution in 1988. ²⁶

Today's Ureteral Access Sheaths

The first ureteral access sheaths were developed in the early 1970s to aid in the passage of nondeflecting passive ureteroscopes and then later in overcoming difficult ureteroscopic access. ^{27 –29} However, these earlier sheaths were cumbersome to deploy, and thus, did not gain general acceptance. It took 30 years before the ureteral access sheath was revisited. Using newer and more hydrophilic material that could not kink, these sheaths, ranging in size from 11 to 16F and in differing lengths to reach the distal, mid, or proximal ureter, began to be commonly used. ²⁹ The ureteral access sheath and its obturator are passed over a stiff guidewire (e.g., Amplatz Super Stiff™); in most cases, this would be a “working” guidewire with a safety guidewire left outside the sheath for use should a ureteral perforation or partial transection occur. With the access sheath in place, a ureteroscope could be passed as many times as the surgeon desired without any shear trauma to the urothelium; use of the ureteral access sheath appeared to also facilitate the basketing and removal of small stone fragments, aid in stent placement, decrease case time, and potentially increase the longevity of the flexible ureteroscope. ^30,31

In 2001, Kourambas and coworkers reported on the advantages of using a 12/14F (inner diameter/outer diameter) ureteral access sheath during ureteroscopy. They noted that it reduced operative times and costs and often allowed for dilation of the ureter without preplacement of a ureteral stent or the need for intraoperative balloon dilation. ²⁹ Rehman and colleagues demonstrated reduced intrarenal pressures and less intravasation of irrigant when an access sheath was used for ureteroscopy in a cadaveric model. ³² Increased irrigation pressures without a concurrent rise in intrarenal pressure may also aid in clearing out stone debris in difficult to reach calices, thereby improving stone clearance rates. ³⁰

Despite their advantages, there have been concerns of operative complications and ureteral injury associated with ureteral access sheath usage. Lallas and colleagues, working with a porcine model, found a reduction in ureteral blood flow with ureteral access sheath use; the reduction in blood flow was directly proportional to the diameter of the sheath. However, over time the blood flow returned to normal and subsequent histopathologic analysis showed no evidence of injury 72 h after each procedure, suggesting that the transient decrease in flow was not detrimental. ³³

Traxer and colleagues reported a 46.5% rate of ureteral injury after access sheath placement in a series of 359 patients from two institutions; however, their classification system included minor ureteral petechiae within the scope of “injury.” In addition, they did not report on stricture rates and long-term complications in these patients. They also routinely used a safety guidewire alongside the access sheaths, which increases the force required for insertion ³⁴ and may contribute to an increased injury rate. ³⁵ In contrast, another study by Traxer and colleagues in 2015 using data from the Clinical Research Office of the Endourologic Society URS Global Study consortium of 2239 patients found no difference in stone-free rates or ureteral damage and bleeding in those treated with or without a ureteral access sheath; the same study actually found a reduced incidence of postoperative infectious complications with ureteral access sheath use. ³⁶ With regards to the concern of ureteral stricture formation, Barbour and Raman found no association between access sheath use and ipsilateral hydronephrosis in their series of 324 ureteroscopies. ³⁷ Delvecchio and colleagues found only one ureteral stricture in a series of 71 patients, in which a ureteral access sheath was used and placed over a guidewire, ³⁸ which is comparable with reported 0%–4% rates of postureteroscopy strictures among patients in whom no ureteral access sheath was used. ³⁹

Ureteral access sheath placement also facilitates endoscopically guided access during PCNL, a technique that allows for direct visualization of nephrostomy needle placement into the collecting system. Use of a ureteral access sheath aids in securing a “through-and-through” guidewire, subsequent tract dilation, and placement of the 30F Amplatz sheath into the collecting system for this technique. ^30,40 Indeed, the development of today's ureteral access sheaths, in part, obviated the need for the safety guidewire as it greatly facilitated reintroduction of the ureteroscope and provided an easy system for placement of a ureteral stent at the end of the procedure.

Demise of the Safety Guidewire

As the use of the safety guidewire was being obsoleted by the ureteral access sheath, reports began appearing of effective ureteroscopy without any guidewire in place. All of the following reports focus specifically on ureteroscopic stone removal and not PCNL. In 2006, Johnson and colleagues reported on 227 “wireless” ureteroscopies, both diagnostic and therapeutic; it should be noted, however, that 2% of their ureteroscopies were for the purposes of assisting PCNL. ⁴¹ Following on this work was that of Patel and colleagues, who reported a 2.6% overall complication rate in a series of 268 ureteroscopies without a safety guidewire, among which there were no perforations or avulsions. ⁴²

Dickstein and colleagues ⁴ presented a series of 306 ureteroscopies by a single surgeon, of which 270 (89%) were uncomplicated and no safety guidewire was used. Among these, there were no cases of ureteral perforation or avulsion, lost access, or need for a postoperative nephrostomy tube. In the remaining 11% of cases, a safety guidewire was used because of an encrusted stent, aberrant anatomy, stricture, or an impacted ureteral stone. ⁴

In 2013, Ulvik and colleagues retrospectively analyzed ureteroscopic stone removals performed at two different academic hospitals in Norway, one in which a safety guidewire was used 96% of the time and another where it was used only 1% of the time. They found no differences in ability to enter the ureter, gaining access to the stone, or deploying a ureteral stent between the two hospitals. In addition, there was a higher stone-free status and lower complication rate at the hospital that rarely used the safety guidewire. ⁶

Disadvantages of the Safety Guidewire

Although the foregoing studies show that the safety guidewire can be eliminated without compromising ureteroscopy, recent studies have begun to question whether the safety guidewire is indeed an impediment to ureteroscopy. To wit, Eandi and colleagues, ³ in an ex vivo porcine study, measured the amount of force required to introduce a ureteroscope into a ureter alongside a safety guidewire. They found that the safety guidewire significantly increased the amount of force required to introduce either a semirigid or a flexible ureteroscope. ³ Taking this into the clinical realm, in a randomized crossover study, Ulvik and colleagues measured the force required for movement of a 8.5F semirigid ureteroscope with and without a Nitinol safety guidewire in place in 40 patients undergoing endoscopic treatment for stones in the renal pelvis; both insertion and retraction forces were measured at four separate locations along the upper urinary tract. They found a statistically significant 52%–113% increase in the advancement and retraction force required to move the ureteroscope when the safety guidewire was in place across all locations of the upper urinary tract. ⁷

Conclusions

The safety guidewire served an important function in providing for safer percutaneous and ureteroscopic procedures during the initial score of endourologic history. However, the decrease in the size of today's ureteroscopes coupled with the advent of effective ureteral access sheaths and the evolution of endoscopic percutaneous renal access has largely eliminated the need for the safety guidewire in both ureteroscopic and percutaneous procedures. Indeed, what was once a “help” may now be more of a “hindrance,” as recent studies have shown that the safety guidewire increases the resistance to passage of the ureteroscope.