Extracorporeal shock wave lithotripsy (ESWL) is a non-invasive method in which high intensity sound waves (shock waves) are generated outside of the patient body and then focused on the stone within the kidney or ureter.

The focal point of the shock wave is fixed, and the patient is moved so that the stone (imaged by fluoroscopy or ultrasound) rests at the focal point (F2 for electro hydraulic Lithotripters). The urologist controls three parameters; number of shock waves administered on the ESWL, the shock wave repetition rate of the Lithotripter, and the voltage (or energy) of the shock wave generator of the ESWL.

The process of stone comminution is monitored by imaging, and treatment is terminated when it is judged that residual fragments are small enough to be voided in the urine or grasped and removed using transurethral or Percutaneous probes. A variety of factors are weighed in determining a treatment protocol, including the number, size, location and suspected composition of the stones, the age and health of the patient, and the type of lithotripter being used. Most ESWL patients are treated as outpatients. 

As a rule stones between 4mm to 20mm are best treated with ESWL.  For stones between 20-30mm, ESWL is still the first line treatment unless factors of stone composition, location, or renal anatomy shift the balance toward invasive but definite treatment modalities (PCNL or RIRS).  Stones grater than 30mm should be primarily treated by PCNL, unless specific indications for RIRS are present (i.e. bleeding diathesis, obesity, etc).