Before 1980, the majority of patients with urolithiasis and nephrolithiasis needed surgery (Kerbl, Rehman, Landman, Lee, Sundaram, & Clayman, 2002; Soucie et al., 1994). Fortunately, percutaneous nephrolithotomy, ureteroscopic intrarenal surgery, laparoscopic surgery, and extracorporeal shock wave lithotripsy (SWL) now allow almost any calculus to be removed without open surgery. SWL refers to the use of high intensity pressure pulses, generated outside the body, to break up kidney stones (Chaussy, Brendel, & Schmiedt, 1980; Loske, 2007). It has become the standard treatment for the majority of patients and an alternative in the management of gallbladder stones, pancreatic concrements, and salivary gland stones. Even though initial studies concluded that shock waves had no damaging effect on renal tissue, later several authors reported that shock waves may cause tissue trauma (Evan, Willis, Connors, McAteer, & Lingeman, 1991; Evan, Willis, & Lingeman, 2003 Willis et al., 1999). Fortunately, techniques and devices are still evolving and improvements to increase stone fragmentation efficiency and reduce tissue trauma are being constantly sought.
Key Terms in this Chapter
Lithotripter: A device to perform SWL, composed of a shock wave generator, a focusing unit, an imaging system, a coupling device, and a patient treatment table.
Focal Zone: Volume in which the pressure at any point is equal to or higher than 50% of the maximum peak positive pressure.
Dual-Pulse Shock Waves: Shock waves generated with a dual-head lithotripter. Dual-pulse shock waves are not necessarily equivalent to tandem shock waves.
Shock Wave: Mechanical wave of high amplitude that arises when any elastic medium is subjected to a rapid compression.
Tandem Shock Wave: Consecutive shock waves having a delay of up to several hundred microseconds, used in SWL to enhance cavitation bubble collapse and, as a result, increase fragmentation efficiency.
Acoustic Cavitation: Growth and collapse of vapor bubbles because of a fast change of positive pressure into tensile stress, produced by a shock wave.
Rise Time: Time needed for the pressure peak to rise from 10% to 90% of its final value.
Peak Negative Pressure: Maximum pressure amplitude of the negative pulse of a shock wave, that is, the difference between the minimum pressure and the ambient pressure.
Fragmentation Coefficient: For in vitro kidney stone fragmentation, the fragmentation coefficient is defined as FC = (Wi – Wf)100/Wi. In this equation, Wi and Wf stand for the weights of the initial (intact) stone and final stone fragments.
Peak Positive Pressure: Maximum pressure amplitude of the positive pulse of a shock wave, that is, the difference between the maximum pressure and the ambient pressure.