Approval from the Ethics Committee of Animal Care of East Attica County was obtained before commencement of this study. Fourteen white male pigs with an average weight of 26 kg were divided in two groups, the RFA-group, and the control (C) group.
Anesthesia protocol
A single dose of prophylactic cefamandole was given preoperatively. Induction to anesthesia was managed by administration of pentothal 8 mg/kg, pancuronium 0.15 mg/kg and fentanyl 17.5 μg/kg. Under general anesthesia the animals were placed in the supine position, intubated with a double-lumen endotracheal tube, and mechanically ventilated. Two large-bore vein catheters were placed for intravenous fluid and drug administration. Maintenance to anesthesia was managed by administering of pentothal at 3.5 mg/kg/h, pancuronium at 0.07 mg/kg every 20 minutes and fentanyl at 15 μg/kg/hr iv. The animals were placed on the right lateral decubitus position. Their vital signs were closely monitored during the operative procedure.
RFA Device
For the RFA group a Radionics Cooltip Radio Frequency System (Radionics Inc., Burlington, MA) consisting of a radiofrequency generator, a peristaltic perfusion pump, grounding pads, and the appropriate electrodes was used. The electrodes were single-shaft, 15 cm long, with a 2 cm exposure tip. The mode was set to "manual" and the timer was off.
Surgical Technique
For the RFA-group, after collapsing the left lung, a mini lateral thoracotomy was performed. After entering the thoracic cavity a small rib retractor was placed, and the lingula of the lung was retracted with a non-crashing clamp. The RFA needle electrode was inserted in the pulmonary parenchyma and the radiofrequency generator was activated by gradually increasing the output to maximum. At the end of the session a spherical zone of coagulative necrosis with a radius of 2 cm was achieved. A series of such overlapping spheres of thermal coagulation were created along the intended line of wedge resection, one next to the other, for completing the plane of resection. Following this, a lung tissue of 4 cm in diameter was divided along the ablated zone by using surgical scissors. After removal of the lung specimen, a 1 cm coagulated zone was left behind along the resection margin to ensure the sealing of blood vessels and terminal bronchial structures.
In cases of minor bleeding at the site of lung resection or air leak after lung expansion, the lung was re-excluded from ventilation, the cut surfaces were approached and additional RFA was applied with the tissue compressed together to enhance the ablation effect. Finally the lung was tested under water for air leakage with application of 20 cm H2O intrabronchial pressure. Covering it with parietal pleura or any other aerostatic or hemostatic technique did not reinforce the cut surface of the divided lung. With regard to the C-group, following thoracotomy the lung parenchyma of the lingula was grasped with a lung retraction clamp and pulled away. A concave, oblique, non-crashing clamp was placed proximally to the pulmonary lateral edge thus creating a 4 cm in diameter lung tissue specimen. The lung tissue peripheral to the clamp was cut with scissors and the pulmonary parenchyma left was repaired with a double row suture using prolene 4-0.
In both groups, before thoracotomy closure a small caliber chest tube was placed two interpleural spaces below the thoracotomy incision and put under gentle suction until completion of chest closure. After skin closure the chest tube was removed and a chest x-ray was done 4 hours after, for pneumothorax exclusion. All the animals were successfully extubated and after having a chest x-ray, they were transferred to their facilities.
Specimen collection
Two tissue specimens were collected from the resected pulmonary parenchyma in both groups. One specimen was collected from the pulmonary healthy tissue before the procedure and the second one near the radiofrequency ablation line immediately after resection. The specimens were sent for TNF and MDA analysis. Samples were frozen at -70°C to prevent further loss of MDA and new sample oxidation. They were also protected from light to prevent photoxidation.