An animal model for assessment of heat distribution and neural damage around the endo shears coagulation device-applications for laparoscopic nerve-sparing surgery.

BACKGROUND AND PURPOSE Current urologic laparoscopic procedures include preservation of locoregional nerve fibers. The use of electrical coagulation is limited because of tissue conductance of current and heat production. While ultrasonic coagulation does not use electricity, heat is still produced. We designed an animal model to characterize the heat spread around ultrasonic devices and assess whether it is neurodestructive. MATERIALS AND METHODS 10 rats were anesthetized; their skin was reflected, exposing the muscles. An ultrasonic probe was introduced into the tissue, and coagulation was performed for 10 seconds. Tissue temperature was measured using four thermocouples, at distances of 4, 8, 12, and 16 mm from the probes and in a circumferential manner. Thermal mapping of the probes was performed with an infrared camera. Further, four rats were anesthetized; the skin above their inner thighs was reflected bilaterally exposing the "nervus ischiadicus." Coagulation was performed in varying distances from the nerve on one side while the other served as control. One week later, the animals were sacrificed, and the nerves were obtained. Silver staining was used to assess the vitality of the axons. RESULTS In distances of 4 to 8 mm from the device, temperatures as high as 81°C were recorded, and silver staining showed severe axonal damage. CONCLUSIONS Although ultrasonic coagulation is efficient, local heat production may reach neurodestructive levels with a typical tissue distribution pattern. These features should be addressed during laparoscopic dissection and when considering nerve-sparing procedures.