Version May 2024
INTRODUCTION — Electrohydraulic lithotripsy (EHL) is primarily used in the endoscopic fragmentation of bile [1-15] and pancreatic duct stones [5,16,17].
An advantage of EHL compared with other methods for treating difficult stones is that it is portable, rapid, efficient, and relatively inexpensive. EHL is typically used during peroral or percutaneous choledochoscopy or peroral pancreatoscopy. (See "Cholangioscopy and pancreatoscopy".)
EHL has also been used for treatment of urinary tract stones, a setting where it has largely been replaced by other methods to achieve stone fragmentation (particularly Holmium laser lithotripsy). Laser lithotripsy for bile duct stones has not been widely adopted, in part because of the costs and limited availability of equipment [18], but Holmium laser lithotripsy has been used successfully at various endoscopy centers, including ours, for the management of biliary and pancreatic stones [19]. (See "Laser lithotripsy for the treatment of bile duct stones".)
This topic review will focus on the technical aspects and efficacy of EHL in the management of bile duct and pancreatic duct stones. Other methods for treating bile and pancreatic duct stones, including laser lithotripsy, extracorporeal shock wave lithotripsy, and standard mechanical lithotripsy, are discussed separately. (See "Laser lithotripsy for the treatment of bile duct stones" and "Extracorporeal shock wave lithotripsy for pancreatic stones" and "Endoscopic management of bile duct stones".)
THEORETICAL BACKGROUND — The principle of electrohydraulic lithotripsy (EHL) is the creation of an electric high-voltage spark between two isolated electrodes located at the tip of a fiber. The electric sparks are delivered in short pulses that create an immediate expansion of the surrounding liquid, inducing a spherical shock wave. The shock wave oscillates, generating sufficient pressure to fragment the stone. In vitro studies using chalk to simulate a stone and a 3.3 Fr probe have demonstrated that short pulses of high peak pressure provided by a low capacity and a high voltage have a greater impact on fragmentation than the corresponding broader shock waves of lower peak pressure carrying the same energy [20]. Application of EHL is best achieved under direct visualization, since shock waves can also injure normal tissue.
EQUIPMENT AND TECHNIQUE — Most endoscopists use the peroral route to perform electrohydraulic lithotripsy (EHL) on bile duct stones [21], while the peroral or intraoperative approach is used for pancreatic duct stones [1-17]. The percutaneous approach is usually reserved for peripheral or pre-stricture intrahepatic stones. Percutaneous choledochoscopy and EHL can be used in patients after surgery that precludes reaching the bile duct perorally. EHL can also be performed laparoscopically or intraoperatively [13-15]. Intracorporeal lithotripsy can be used in conjunction with extracorporeal lithotripsy in patients with stones that are difficult to remove [3,4,6,8]. This approach increases the success rate and decreases the need for surgical intervention. (See "Cholangioscopy and pancreatoscopy" and "Percutaneous transhepatic cholangioscopy".)
We use a digital single-operator cholangioscope (SpyGlass DS, Boston Scientific Corporation, Natick, MA, USA), which uses a 10.5 Fr scope mini-endoscope (also known as a "daughter scope") that is passed through the accessory channel of a therapeutic duodenoscope. It is a digital endoscope with a 1.2 mm working channel for therapeutic intervention and use of accessories. In addition, it has a separate irrigation channel. A feature of this device is that it has four-way tip deflection, in contrast with standard choledochoscopes, which have two-way deflection. We have used this system for peroral treatment of biliary and pancreatic stones, and also percutaneously in patients after pancreatoduodenectomy who developed a biliojejunal anastomotic stricture and formed a stone proximal to it. (See "Cholangioscopy and pancreatoscopy".)
The EHL fiber measures approximately 1.9 to 3.3 Fr, or 0.66 to 1.1 mm. The available mini-endoscopes have a working channel of 1.2 mm. Thus, space around the EHL fiber within the channel is almost nonexistent when larger probes are used. As a result, great care must be taken when advancing the EHL fiber through the channel of the choledochoscope to avoid bending or breaking. Because the EHL fiber is rigid and can easily damage the inside aspect of the bending part of the mini-endoscope, it is best to attempt to straighten the mini-endoscope when advancing the EHL fiber. We lubricate the accessory channel of the mini-endoscope with liquid silicone before inserting the EHL fiber. The EHL fiber is not advanced into the bile duct unless the stone is well visualized. Once the EHL fiber is advanced, the mini-endoscope is usually pushed forward to achieve a "long" position, a maneuver that permits straightening of the bending portion of the mini-endoscope. Another useful tip is advancing the fiber while simultaneously pushing water through the channel. If the above steps fail to advance the fiber, pushing the mini-endoscope up into the proximal bile duct can facilitate fiber advancement.
Once outside the mini-endoscope, the EHL fiber tip can be seen both endoscopically and fluoroscopically (figure 1). Whenever possible, the EHL fiber is pushed against the center of the stone. An approach using a balloon to help center the fiber has been described, a technique performed without a choledochoscope. However, this technique is too risky since it can cause epithelial injury with potential secondary perforation. If there is no other option to center the fiber to the stone, we fire the probe tangentially, but avoid any contact with the bile duct wall. This may permit "chipping" of the stone, which may then allow for better accommodation against the probe. The tip of the fiber should be as close to the stone as possible. The stone can be touched if needed. However, touching the stone may reduce the functional lifespan of the probe itself. EHL is delivered according to a preset power wattage (usually in the range of 70 to 100 watts) via 1 to 2 seconds or continuous pulsations. We start at a power of 70 watts and increase it by 10 watts as needed to a maximum of 100 watts. Continuous saline irrigation into the bile duct is used to generate a fluid medium and magnify the EHL power (approximately 10-fold). The probe will not work unless it is in a fluid medium. Both the probe tip and stone surface need to be in an aqueous environment for fragmentation to occur. It also aids in flushing out debris and facilitates visualization. Another EHL generator (Autolith, Boston Scientific Corporation, Natick, MA, USA) is a computer-controlled generator that simplifies the settings of EHL such that watts are adjusted to preset power settings.
Once fragmentation of the stones is complete, the mini-endoscope is withdrawn and the stones are removed using standard methods (figure 1). EHL can also be successfully performed on stones located above a bile duct stricture or when, upon attempting stone removal with a basket, the basket-stone complex becomes impacted in the distal bile duct and cannot be removed or dislodged (image 1).
EFFICACY
Bile duct stones — The overall success rate for biliary electrohydraulic lithotripsy (EHL) exceeds 90 percent [1-15,22-25] when considering reports using varied routes to access the biliary tree and including reports in which EHL was used in conjunction with other methods such as extracorporeal lithotripsy [6,8]. The following studies illustrate the range of findings:
●One report focused on 65 of 108 patients with difficult stones who underwent EHL via peroral choledochoscopy [3]. Stone removal was successful in all patients except for one in whom the choledochoscope could not be introduced.
●Another report described the long-term experience in 55 patients with intrahepatic stones that were not accessible to routine endoscopic extraction [6]. Extracorporeal shock wave lithotripsy (ESWL) was used in 27, EHL in 12, and laser lithotripsy in 16. Stone fragmentation was achieved in 33, 42, and 75 percent, respectively. The success rate increased to more than 90 percent when the different methods were combined.
●A third study included 125 patients with common bile duct stones in whom conventional endoscopic treatment failed. EHL was used in 46 patients and ESWL was used in 79 patients [8]. ESWL could fragment stones in 68 patients and the bile duct was cleared of stones in 62 patients, for a success rate of 79 percent. EHL successfully fragmented and cleared the stones in 38 patients, for a success rate of 77 percent. When the treatment modalities were combined, the overall success rate was 94 percent.
●Another study described the use of EHL without cholangioscopy in a total of 19 patients with bile duct stones that could not be removed with standard methods [26]. The authors advanced a 3.0 F radio opaque EHL probe through a balloon catheter. EHL was performed under fluoroscopic guidance until the stone was fragmented small enough to be captured with a mechanical lithotripsy basket. The bile duct was cleared in 16 patients (84 percent). However, additional mechanical lithotripsy was required in 9 of the 16 patients. Complications included hemobilia in two, pancreatitis in one, and cholangitis in one. While this may be the only alternative in some patients, the overall success rate was lower than expected for standard EHL and not using direct endoscopic visualization may increase risk. Thus, we continue to recommend that EHL should be performed only under cholangioscopic guidance.
●A fifth study compared biliary stenting with EHL in 36 high-risk patients with retained common bile duct stones [27]. Nineteen patients underwent double pigtail stenting and 17 underwent EHL with an attempt at complete stone removal. Only 77 percent of the patients undergoing EHL achieved stone clearance, whereas the success rate of stent introduction was 95 percent. During follow-up, there was a significant increase in recurrent cholangitis and mortality due to recurrent cholangitis in the stent group compared with the EHL group (63 versus 8 percent and 21 versus 0 percent, respectively). This study further emphasizes that achieving complete stone clearance even in the high-risk patients is the better option [27].
●In a systematic review including 32 studies and 1969 patients, laser lithotripsy was associated with higher rates of complete ductal clearance compared with EHL and extra-corporeal shock wave lithotripsy (ESWL) (95 versus 88 and 85 percent, respectively) [28]. However, this review included studies using older EHL generators, and in our experience, the automated EHL generators perform better than older models and are comparable to holmium laser lithotripters.
EHL has also been compared with sequential biliary stenting for removing stones that could not be removed with conventional endoscopic treatments. In a retrospective study of 439 patients who underwent ERCP for stone removal, 43 failed conventional endoscopic therapy and were managed with sequential biliary stenting (36 patients) or with EHL (seven patients) [29]. Ductal clearance was achieved in 100 percent of EHL patients after an average of 1.3 procedures per patient. Of the patients in the sequential biliary stenting group, ductal clearance was accomplished in 86.1 percent after 2.8 procedures per patient. There were more complications in the stented group.
Pancreatic stones — EHL has also been used in the treatment of pancreatic stones [5,16,17,30]. In a retrospective study including 109 patients with pancreatic duct stones, rates of ductal clearance were not significantly different for EHL compared with laser lithotripsy (94 versus 100 percent) [30]. In addition, adverse events were not significantly different between groups.
Some reports have focused on patients with impacted stones in the setting of chronic calcific pancreatitis. One report, for example, included five patients who had failed extracorporeal shock wave lithotripsy and one patient who developed recurrent pancreatic stones after surgery [17]. Patients were treated with a total of nine intraductal EHL procedures. Complete or partial pancreatic duct clearance was achieved in all but one patient. The five patients in whom the duct was partially or completely cleared experienced complete relief of abdominal pain for at least six months. No complications were observed.
Fragmentation of an impacted pancreatic duct stone that failed ESWL has been reported [31]. The EHL probe was advanced to the stone housed in a balloon under fluoroscopic control without direct visualization. Although the intervention was successful, EHL should be performed under direct visualization to avoid ductal injury.
Other uses — EHL has been successfully used in patients with duodenal obstruction secondary to biliary stone, in patients with gallstone ileus, and in patients with stones after orthotopic liver transplantation [32-34].
ADVERSE EVENTS — The most serious adverse event associated with EHL is perforation of the bile duct, which can occur if the EHL probe touches the bile duct wall. However, perforation of the bile duct is rare. Perforation can also occur due to extreme elevation of the surface temperature of the stone and surrounding ductal tissues, which is usually caused by prolonged application of EHL. The overall risk is probably less than 1 percent; in our own experience with over 500 patients, we have not encountered any perforations. Bleeding can also occur from touching the wall of the bile duct with the probe. The overall risk is also probably less than 1 percent. We encountered two patients with self-limited bleeding among 43 treated patients.
Other risks are mostly related to endoscopic retrograde cholangiopancreatography. (See "Overview of endoscopic retrograde cholangiopancreatography (ERCP) in adults".)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Chronic pancreatitis and pancreatic exocrine insufficiency" and "Society guideline links: Biliary infection and obstruction".)
SUMMARY AND RECOMMENDATIONS
●Background – Electrohydraulic lithotripsy (EHL) is primarily used in the endoscopic fragmentation of difficult bile and pancreatic duct stones. (See 'Introduction' above.)
The principle of EHL is the creation of an electric high-voltage spark between two isolated electrodes located at the tip of a fiber. The electric sparks are delivered in short pulses that create an immediate expansion of the surrounding liquid, inducing a spherical shock wave. The shock wave oscillates, generating sufficient pressure to fragment the stone. (See 'Theoretical background' above.)
●Efficacy – The overall success rate for biliary EHL exceeds 90 percent when using varied routes to access the biliary tree and when using EHL in conjunction with other methods, such as extracorporeal lithotripsy. (See 'Efficacy' above.)
●Adverse events – The most serious adverse event associated with EHL is perforation of the bile duct; however, the risk of perforation is low (ie, approximately less than 1 percent). (See 'Adverse events' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Susana Escalante-Glorsky, MD, and Isaac Raijman, MD, who contributed to earlier versions of this topic review.
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