Ultrasonic lithotripsy and soft tissue

Abstract

It has been suggested that ultrasonic lithotripsy causes soft tissue damage by cavitation processes, by DNA alterations at subcavitational ultrasound levels, by thermic and mechanical trauma from the probe and from metal fragments splintered off the sonotrode. These issues were investigated in vitro and in vivo in the leporine bladder. Ultrasound intensity levels measured at the tips of sonotrodes never exceeded the cavitation threshold, so that cavitation processes are not involved in ultrasonic lithotripsy. The incidence of sister chromatid exchange in growing human lymphocytes was not altered, so that mutagenic effects appear unlikely. Thermic damage by the sonotrode is reliably prevented by irrigation cooling with 20 ml/min saline (20°C); higher flow rates are necessary for adequate vision in clinical practice. In spite of vibration amplitudes of up to 50 μ, the sonotrode causes only mucosal abrasion and submucosal hemorrhage; lesions of deeper layers of the bladder wall were never observed. Metal fragments are splintered off the sonotrode and nephroscope by contact, and this can largely be prevented by teflon coating of the wands. The fragments were washed out of leporine bladders within 24 h when instilled into the bladder cavity, and within 7 days when rubbed into the mucosa. In conclusion, significant soft tissue damage by ultrasonic lithotripsy was not observed. This corresponds to clinical experience with technique in 518 kidneys.