LITHOTRIPTER ENERGY SOURCE Dr. C S RATKAL M.S, M.Ch Professor & HOD of Urology Institute of NephroUrology Bangalore
The efficiency of the lithotrite is the most important requirement and size and flexibility are of secondary importance. • The urologist who treats patients suffering from urolithiasis thus requires an armamentarium of intracorporeal lithotripsy devices, each maximizing a different quality (e.g., size, flexibility, efficiency).
TYPES OF LITHOTRIPSY ENERGY SOURCES: EXTRACORPOREAL INTRACORPOREAL
INTRACORPOREAL LITHOTRIPSY • Four techniques are available for intracorporeal lithotripsy: • electrohydraulic lithotripsy (EHL), Flexible • laser lithotripsy , • ultrasonic lithotripsy, Rigid • and ballistic lithotripsy.
Electrohydraulic Lithotripsy.Mechanism The EHL probe is essentially an underwater spark plug composed of two concentric electrodes of different voltage polarities separated by insulation. When a current sufficient to overcome the insulative gap is applied, a spark is produced formation of a plasma channel and vaporization of the water hydraulic shockwave followed by formation of a cavitation bubble collapse of the cavitation bubble may be symmetrical , resulting in a strong secondary shockwave, or asymmetrical - leading to the formation of high-speed microjets
Technique of EHL The EHL fiber tip positioning Procedure- Firing time of probe 50 to 60secs Probe life
The major disadvantage of EHL is its • ureteral perforation. • retrograde propulsion of calculi and fragments • Danger to guide wire & baskets • Fragment size larger compared to laser
ADVANTAGES OF EHL • EHL will successfully fragment 90% in 90% of stones. • probe flexibility & size • least costly intracorporeal device.
Laser is an acronym for light amplification by stimulated emission of radiation Stimulation of Atom by external energy source ↓ electrons in excited state ↓ release of photons/ light energy it is coherent - all photons are in phase with one another, collimated- photons travel parallel to each other, and monochromatic- all photons have the same wavelength Laser Lithotripsy
named after the medium that generates their specific wavelength of light • first medium used was the ruby- continuous wave which generated lot of heat and hence not appropriate for clinical use • pulsed energy results in high-power density at the stone’s surface but little heat dissipation • The first widely available laser lithotrite was the pulsed-dye laser- cysteine and calcium oxalate monohydrate difficult to fragment, coumarin dye toxic agent with disposal as issue, eyewear made visualisation difficult.
The holmium laser is a solid-state laser system, wavelength of 2140 nm in the pulsed mode. absorbed superficially, which results in superficial cutting or ablation. The zone of thermal injury from 0.5 to 1.0 mm Mechanism of action- primarily through a photothermal mechanism that causes stone vaporization HOLMIUM LASER
begin with low-pulse energy with a pulse rate of 6 Hz & ENERGY 0.6J and increase pulse frequency in preference to increasing pulse energy as needed to speed fragmentation Move the laser fiber over the stone surface in a “painting” fashion, . The laser fiber should be kept at least 1 mm from the urothelium & 2mm from tip of the scope “SNOW-STORM EFFECT” FIBRE SIZE TECHNIQUE
Advantages- • transmit its energy through a flexible fiber, • fragment all stones regardless of composition • safely activated at a distance of 0.5 to 1 mm from the ureteral wall- one of the safest, most effective, and most versatile • significantly smaller fragment • Weakshockwave, which reduces the likelihood of retropulsion of the stone • Perforation & stricture rate is 1-2% • No protective eye wear required- 10 cm safe distance • Ready for use within a minute of turning on • Minimal maintenance
major disadvantage of the holmium laser is the initial high cost of the device and the cost of the laser fibers the smallest fiber in widespread use, the 200-μm fiber, impedes deflection of a flexible ureteroscope by up to 20 degrees. fracture of a laser fiber inside of an endoscope can result in a catastrophic failure of the scope Production of cyanide ??? • DISADVANTAGES OF HOLMIUM LASER
Rigid Lithotripters • Ballistic Lithotripsy. Ballistic lithotripsy relies on energy generated by the movement of a projectile • “Jackhammer” effect- Flexible objects preserve the momentum of the energy, but inflexible objects, such as a stone, fragment on impact.
Rigid Lithotripters • Swiss LithoClast, first ballistic lithotrite. The metal projectile in the handpiece is propelled by measured bursts of compressed air against the head of a metal probe at a frequency of 12 cycles per second. Utilises hospital central air supply or compressed air tank. • The electrokinetic lithotripter consists of a rheostat and a handset containing an electric coil that generates an electromagnetic field, which then vibrates the probe at 15 to 30 cycles/sec. • Stone Breaker(Rane)
Technique of ballistic lithotripsy: • Activate only when stone is in full view and probe is identified. • Fixation of stone in capacious ureter may be difficult. Use of basket or uretral occlusion balloon may be necessary. • Relatively atraumatic nature may allow avoidance of stent placement after URS.
Advantages- • Very effective with wide margin of safety. • Successful fragmentation of all compositions from 70%- 100% • Pin down the stone • Can be used with ultasonic device • significantly lower risk of ureteral perforation • no heat • Relatively low cost and low maintenance. • no disposable costs and • the probes have an extremely long life span
Disadvantages • Rigid in nature • relatively high rate of stone retropulsion • reduced efficiency with semirigid ureteroscope • bowing of the probe during lithotripsy results in significant power loss • Multiple passes into the ureter to retrieve caluli since fragments usually larger than 4mm size. • Water back-leak into handpiece
Components • Compressed air supply : 5-6 bar • Blast power: 3-4 bar • Operating mode :- single/ multiple pulse • Hand piece : 300-350gms • Probe – 0.8mm, 1.0, 1.2, 1.5, 2.0, 2.5mm. • Length – 425/620 mm • 1mm, 1.6mm, 3.2mm
2 recent improvements – A suction device connecting to the Lithoclast probe allows simultaneous evacuation of stone particles. Flexible nitinol probe allows use of the lithoclast through a flexible ureteroscope.
Ultrasonic Lithotripsy • ultrasound probe works by applying electrical energy to excite a piezoceramic plate in the ultrasound transducer . • plate resonates at a specific frequency and generates ultrasonic waves at a frequency of 23,000 to 25,000 Hz which causes the stone to break but causes minimal damage to the compliant urothelium. • ultrasonic lithotripsy is more efficient during PCNL, owing to the greater flow of irrigant. • Technique- Trap the stone between probe and urothelium. Dont push too hard to avoid perforation.
Adavantages of ultrasonic lithotripsy: • efficient combination of stone fragmentation and simultaneous fragment removal. • particularly useful for large ureteral stones as well as for steinstrasse • Minimal tissue damage • Disadvantages- • Rigid in nature & size of probe limiting factor • Retropulsion of stone • Stones vary in susceptibility to fragmentation with cystine, calcium oxalate monohydrate & uric acid being most resistant. • Other stone factors-size, density more important.
Combination of ballistic and ultrasonic lithotripsy Probes arranged coaxially Each modality activated seperately or coaxially LITHOCLAST ULTRA
In-vitro testing apparatus for a “hands free” testing approach to the evaluation of intracorporeal lithotrites.
Extracorporeal Shockwave lithotripsy • Methods & physical principles- • In extracorporeal SWL a source external to the patient’s bodygenerates a shockwave. Specifically, the energy source rapidly deposits pulses of energy into a fluid environment, which results in the generation of a shockwave • Uniqueness is shockwave focussing of weak, non-intrusive waves generated externally & transmitted through body which cause stone fragmentation by building sufficient strength only at target.
3 types of Generators • electrohydraulic (spark gap), • electromagnetic, • piezoelectric
Electrohydraulic ( spark gap generator) • High voltage to 2 electrodes placed 1mm apart (F1) ↓ • Explosive vaporization of water vapor ↓ • Spherically expanding shock waves focussed at the target (F2). • clear advantage- very effective ( unmodified HM3). • Disadvantages are the substantial pressure fluctuations from shock to shock and a relatively short electrode life.
Displacement of the electrode tip off of F1 can shift F2 off of the initial target.
ELECTROMAGNETIC GENERATOR • Generators produce either :- • Plane waves- focused by an acoustic lens or • Cylindrical waves- reflected by a parabolic reflector and transformed into a spherical waves
Mechanism- uses a water-filled shock tube containing two conducting plates separated by a thin insulating sheet. When an electrical current is sent through one or both of the conductors, a strong magnetic field is produced between the conductors, moving the plate against the water and thereby generating a “ Magnetic” pressure wave. These waves are focussed onto F2 by either acoustic lens or parabolic reflector.
Advantages of electromagnetic lithotripter • more controllable and reproducible • introduction of energy into the patient’s body over a large skin area, which may cause less pain. • a small focal point can be achieved with high-energy densities, which may increase its effectiveness in breaking stones. • deliver several hundred thousand shockwaves before servicing, thereby eliminating the need for frequent electrode replacement
Disadvantage:- the small focal region of high energy results in an increased rate of subcapsular hematoma formation, incidence ranging from 3% - 12%.
Figure 1 The original lens of the EM lithotripter was modified with an annular ring cut 14 mm deep (h) to its lower surface near the source and a corresponding uncut lens area-to total-lens area ratio of 60%. modified the acoustic lens of an EM lithotripter to produce a broader focal zone and an idealized pressure waveform more closely resembling that of the HM3 Source: Journal of Urology, The 2013; 190:1096-1101 (DOI:10.1016/j.juro.2013.02.074 )
Piezoelectric lithotripter • produces plane shockwaves with directly converging shockfronts • mosaic of small, polarized, polycrystalline, ceramic elements (barium titanate), stimulated by the application of a high-voltage pulse . • 300 to 3000 crystals are necessary for the generation of a sufficiently large shock pressure. • The piezoelectric elements are usually placed on the inside of a spherical dish to permit convergence of the shockfront. • The focus of the system is at the geometric center of the spherical dish.
Advantages – • Focusing accuracy • long service life • anesthetic-free treatment. Disadvantage – insufficient power it delivers, which hampers its ability to effectively break renal stones.
Conclusion • Holmium laser is versatile for all type of URS • Combination devices are very useful for PCNL & for bladder stones. • Most patients with uncomplicated kidney stones can best successfully treated with SWL. • Factors to consider when buying a lithotrpiter- number and nature of stone-related procedures performed to • maximize the utility and cost-effectiveness of the device