How is electrohydraulic lithotripsy (EHL) performed for common bile duct stones?

How Electrohydraulic Lithotripsy (EHL) is Performed for Bile Duct Stones

EHL for bile duct stones is performed under direct cholangioscopic visualization using single-operator cholangioscopy (SOC), where a high-voltage spark generates a shock wave that fragments stones through rapid thermal expansion of fluid, achieving 73-97% stone clearance rates when standard techniques fail. 1

Technical Mechanism

EHL works by generating a shock wave through rapid thermal expansion of fluid caused by a high-voltage electrical spark. This creates a subsequent hydraulic pressure wave that causes stone fragmentation. The delivery of this energy must be conducted under direct vision to ensure safety and precise targeting during fragmentation. 1

Procedural Approach

Equipment and Access

• Single-operator cholangioscopy (SOC) is the modern standard approach, using systems like SpyGlass (introduced 2006) or the newer SpyGlass DS digital platform (2015) 1
• The cholangioscope is passed through a duodenoscope during ERCP
• Earlier "mother-baby" systems required two operators and were technically challenging, limiting widespread use 1

Step-by-Step Technique

1. Initial ERCP with sphincterotomy - Standard endoscopic stone extraction techniques are attempted first (basket extraction, mechanical lithotripsy, endoscopic papillary balloon dilation)
2. Cholangioscope insertion - When standard techniques fail, the cholangioscope is advanced through the duodenoscope into the bile duct
3. Direct visualization - The stone is visualized directly under cholangioscopic guidance
4. EHL probe placement - The electrohydraulic probe is positioned against the stone under direct vision
5. Stone fragmentation - High-voltage sparks are delivered to fragment the stone
6. Fragment removal - Fragmented stones are then extracted using standard baskets or balloons

Clinical Indications

EHL is recommended when other endoscopic treatment options fail to achieve duct clearance, specifically after unsuccessful attempts with: 1

• Mechanical lithotripsy
• Endoscopic papillary balloon dilation with prior sphincterotomy
• Standard basket/balloon extraction

This represents a "difficult stone disease" scenario where advanced lithotripsy becomes necessary before considering more invasive options like percutaneous extraction or open surgery 1

Success Rates and Safety

• Stone clearance rates: 73-97% with SOC-guided EHL 1
• Most patients (76%) require only one ERCP session for complete clearance 2
• Cholangitis occurs in up to 9% of patients, necessitating prophylactic antibiotics 1
• Other complications are comparable to conventional ERCP 1

Important Clinical Considerations

Sedation Requirements

For complex procedures like cholangioscopy-assisted EHL, enhanced sedation with propofol or general anesthesia is strongly correlated with therapeutic success due to the lengthy and complex nature of the procedure 1. Standard conscious sedation may be inadequate.

Alternative Approaches

• Percutaneous transhepatic approach: EHL can be performed via transhepatic access when endoscopic approach fails or is not feasible 3, 4
• Direct peroral cholangioscopy: Ultra-slim upper endoscopes can be used as an alternative to the mother-baby system 5

Common Pitfalls

• Never perform EHL without direct visualization - blind instrumentation risks perforation and stricture formation 1
• Ensure adequate biliary drainage - incomplete drainage after stone manipulation increases cholangitis risk
• Consider prophylactic antibiotics - given the 9% cholangitis rate with cholangioscopy 1

Comparison to Laser Lithotripsy

While laser lithotripsy (LL) uses pulsed laser energy rather than electrical sparks, both achieve similar stone clearance rates (73-97%) and both require direct cholangioscopic visualization 1. The choice between EHL and LL depends primarily on equipment availability and operator experience.