First described in 2002, this technique uses RF energy to coagulate the liver resection margins.28 The cool tip probe and a 500 kHz generator produce 100 w of power and enable measurement of generator output, impedance, and tip temperature. The probe contains a 3 cm-exposed electrode, a thermocouple (to measure temperature and impedance), and two co-axial cannulate (through which chilled saline is circulated to prevent tissue boiling and cavitation adjacent to the needle). The generators used in RF thermal ablation are alternating electric current generators that operate in the radio frequency range 200 to 1200 kHz. It is the alternating current that causes thermal injury. The alternating current generator is similar to the electric generator that powers the surgical electric cautery. The primary difference is that, with RF, lower voltage and wattage are used to produce coagulative necrosis. If the tissue is heated too abruptly, as in cauterisation, charring occurs around the electrodes. This markedly limits the size of the thermal injury as a result of the increased resistance. As the ablated tissue dries out, the impedance rises until the electrical circuit is broken (Fig. 3).
In the Habib's technique, initially a line is made on the liver capsule with diathermy to mark the periphery of the tumour, as after RF, the parenchyma is hardened and indistinguishable from tumour. A second line is made 2 cm away from the first line using diathermy,
and RF is applied to the outer line. After the deepest tissue is coagulated, the probe is withdrawn and the cycle repeated. The point of entry of each probe should be 1 cm from the previous. Finally, the liver parenchyma is divided using a scalpel. The division line should be between the two lines so as to leave a 1 cm-resection margin. RF coagulation is applied from within the resection margin, if there is residual bleeding.
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