| Objective: To study whether Saline-Enhanced Radiofrequency Ablation of pulmonary tissue in rabbits could widen necrosis region .To observe the thermal distribution and histological change with the instillation of Saline constantly .Method: Twenty-four New Zealand White rabbits (4～6 months old, 3～3.5kg) were divided randomly into two groups: an RFA group (n=12) and a saline-enhanced RFA (SRFA)group (n=12). And each group was sacrificed at different time intervals after the procedure: procedure today (n=4), after 5 days (n=4), after 10 days (n=4). The rabbits was cannulaed in trachea and connected the animal respirator after the success of anesthesia by 864 mixture. After opening thoracic cavity , the RF electrode was inserted and opened 1cm active tip in the target area of pulmonary tissue which was far away from the vessels and bronchus. The setting temperature is 90℃and the setting power is 70w. When the temperature rose to the 90℃, the instrument maintained the power automatically and would accomplished the RFA procedure in 5 minutes.In the SRFA group, 0.5ml of 0.9% saline was infused slowly in the pulmonary tissue through the pinhole before RFA and 0.5ml of 0.9% saline was infused in the procedure at the speed of 0.01ml/s. To record the data of temperature and impedance at the different time. The two group rabbits were sacrificed at the different time. The lesion of the lung lobe was splitted and the Lesion size was measured by vernier caliper. Then histological change of the lesion was observed.Results: After splitting the lesion, we found that the dividing line between the lesion edge and normal tissue was obvious. In the centray of lesion, tissue was dark brown and fragile, which was surrounded by bleeding and congestion zones. After 5 days of the procedure, the bleeding and congestion zones had gotten little. After 10 days, the dividing line between the lesion edge and normal tissue changed vague.Surrounding tissue was becoming organized into granulation tissue, with an increase of fibroblasts. In the SRFA group, the mean diameter (12.0±0.7mm) at the day, the mean diameter(16.8±0.5mm) after 5 days and the mean diameter (16.3±0.7mm) after 10 days of RF lesions were greater than the mean diameters (9.4±0.8mm; 12.0±0.6mm; 12.0±0.6mm) of RFA group (p<0.05). During RFA, the temperature of SRFA group was low and rose slowly, but changed faster later. The temperature of every needl was not statistically significant (p>0.05). And the temperature of every needl in RFA group was also not statistically significant (p>0.05).The mean time which the RFA group spent on getting to the 90℃was 372.7±7.1s, and that mean time of SRFA was 371.8±9.1s.There was not statistically significant between them(p>0.05). In the beginning of RFA, the tissue impedance(90±12Ω) in the RFA group was greater than that(48±10Ω) in the SRFA group(p<0.05).what is more. In the RFA group, tissue impedance changed markedly (from 90Ωto 820Ω) during the procedure and frequently induced activation of the pulsing technique, whereas in the SRFA group, impedance showed no notable change (range, 45Ω-430Ω). Differences between the two groups in the duration of RF energy instillation before pulsing were statistically significant: 90±11vs. 181±28seconds(p<0.05). Histological examination of an acute lesion revealed a central charred zone with complete destruction of the parenchyma, including a small central cavity where tissue had been lost. Surrounding this were two zones of neosinophilic coagulative necrosis and a peripheral hemorrhagic rim.There was sharp cut-off between ablated lesions and normal lung. Outside this area, viable lung containing acute inflammatory cell infiltrate was present. After 10 days, there were many inflammatory cells and fibrous tissue in the lesion.Conclusion: Saline-enhanced RFA of pulmonary tissue in rabbits producs more exte- nsive coagulation necrosis than conventional RFA procedures, which can equilibrate the thermal distribution and diminish the tissue impedance. And the saline promote dissemination of energy and improve effection of RFA.
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