Determination of temperature elevation in tissue during the application of the harmonic scalpel

The temperature elevation in tissue during the application of the harmonic scalpel (UltraCision, operating frequency 55 kHz; Ethicon Endo-Surgery, Norderstedt, Germany) was determined using thermocouples of a specific design. In experiments with and without perfusion, two different scalpel blades were applied to three different kinds of pig tissue (lung parenchyma, tongue, parotid gland) in various configurations. Temperature elevations by more than 40 degrees C were found at 1 mm distance from the blade, whereas at distances of more than 5 mm, perfusion removed the heat very efficiently. The differences in the heating potential of the two blades were small and, at a distance of 2 mm, the temperature elevation did not exceed 6 degrees C at all. In histological investigations, the damaged area between blade and parenchyma was determined. No morphologic indications of thermal damage were found at a distance of more than 2 mm. It is concluded that, during application of the harmonic scalpel, a safety margin of 3 mm from sensitive structures should be kept.