Beijing Tsinghua Chang Gung Hospital

The present study aimed to examine the relationship of irrigation velocity, operator duty cycle (ODC), and intrarenal temperature during extracorporeal shockwave lithotripsy with a superpulse fiber thulium laser. Calcium oxalate monohydrate stones were implanted in the renal pelvis of fresh pig kidneys. Puncture technology was used to place a temperature probe accurately in the renal parenchyma about 2 mm away from the stone. To simulate the temperature at which a human body is exposed, that is, 37°C, the experiment was executed in an equilibrated laboratory at a constant temperature of 25°C with 60% humidity. The power of the laser varied between 10W and 30W; that of the irrigation varied from 10 to 30 ml/min. The time that the laser was applied was set at 120 s. Changes in the temperature were recorded online. A direct proportionality of temperature in the kidney to the rate of irrigation has been reported between 10 W and 30 W laser powers. The percentage ratio of the rate of irrigation and power in the laser is 1:1, which can keep the temperature in the kidney at a safe level. More specifically, at a laser power of 20 W and irrigation of 10 ml/min, the temperature inside the kidney increases sharply with the increase in ODC. By decreasing the ratio of ODC, the increase of temperature inside the kidney can be brought to a great reduction. The ratio of laser power to that of irrigation speed should be 1:1; hence, damage or injury to kidney tissue can be efficiently prevented from thermal changes.