Bloodless Partial Nephrectomy Through Application of Non-Focused High-Intensity Ultrasound

Abstract

The goal of this study was to evaluate the hemostatic ability of a new interstitial applicator composed of a planar ultrasonic transducer with a reflector, during partial nephrectomy in a porcine model. The new applicator was designed to make effective use of all the acoustic energy to coagulate the renal tissue . Placement of the reflector opposite the transducer allows use of all the acoustic energy for coagulation. Despite the low transmission frequency, it is possible to work at a relatively weak intensity, with the aid of the reflector. As a result, intense cooling of the transducer is no longer needed. The transducer functions at a frequency of 3.78 MHz. A movable brass plate was mounted to the applicator, parallel to the transducer, to reflect energy that was not absorbed during ultrasound wave transmission. Additionally, the plate served to immobilize the kidney during the treatment. Our methodology was to expose the kidneys of 9 pigs through abdominal laparotomy. An initial series of experiments on 5 pigs allowed exposure conditions to be selected. Thermocouples were implanted in the kidneys after exposure at 15, 20, and 25 mm from the renal capsule surface. The remaining 4 pigs underwent ultrasound treatment with the applicator before a bilateral lower pole partial nephrectomy. The treatment consisted of juxtaposing elementary lesions (made at an intensity of 26 W/cm2 for 50 seconds) circumferentially in a subhilar location. The hemostatic efficacy was evaluated just after the shots and during the 30 minutes that followed the sectioning of the kidney’s lower pole. In the event of persistent bleeding, an it was possible form an elementary lesion opposite the insufficiently treated zone. For an exposure duration of 50 seconds at 26 W/cm2, the lesions obtained covered the total thickness of the kidney, which varied between 22 and 36 mm. The temperatures observed within the treated tissues were 62°, 59°, and 58°C at 15, 20 and 25 mm respectively from the kidney surface. The system with the reflector allowed uniform temperatures to be obtained through the complete thickness of the kidney. By applying between 6 and 9 elementary lesions, all partial nephrectomies were performed without hemorrhagic problems, except for one partial nephrectomy (1 of 8 kidneys; 12.5%) for which a central artery could not be controlled. In conclusion, our ultrasound applicator is an excellent hemostatic tool allowing effective coagulation of a highly vascularized organ such as the kidney. The experiment will be repeated for a longitudinal study in order to better verify the persistence of hemostasis. The possibility of adapting this applicator ergonomically as well as the possibility to utilize it for laparoscopy is presently under investigation.