Lung metastases are frequently removed with an Nd:YAG laser. The aim is to perform a non-anatomic resection of all intraoperatively palpable lung metastases completely in order to preserve the largest possible amount of healthy lung parenchyma. The surgeon can either work with a focusing handpiece or use a laser fiber of the so-called bare fiber with direct contact to the lung parenchyma. We currently use a 600 µm bare fiber for applications involving the lung parenchyma. Precise data on the local effect of the laser fiber on the lung parenchyma are not available, especially with regard to an increase in the laser energy. We want to study this question within the scope of an experimental model in pig lungs by means of systematic and reproducible tests. The lung lobes were removed from animals recently slaughtered in the abattoir and taken to the laboratory immediately, where the lobes were stored such that the surface of the lungs was parallel to the floor. A 600 µm bare fiber was attached to a mounting bracket vertically above the lung surface at a distance of either 0, 5, or 10 mm. This mounting bracket was in turn connected to a hydraulic feed motor. The feed motor is capable of moving the bare fiber forward across the lungs consistently at three different speeds (5 mm/s, 10 mm/s, or 20 mm/s). The bare fiber itself was connected to the diode-pumped Nd: YAG Laser LIMAX®
120 (Gebrüder Martin GmbH & Co KG, Tuttlingen, Germany). We carried out the tests using three different laser powers: 20 W, 60 W, and 120 W. The lung lesions caused by the laser in each of the lungs were resected and sent in for histological analysis. The exact size of the vaporization and coagulation zone was measured using the HE sections, and the respective mean values (with standard deviations) were ascertained. For all laser powers, the extent of the vaporization was greatest with a motion speed of 5 mm/s for the respective laser power: 756.4 ± 1.2 µm (20 W), 1411.0 ± 2.3 µm (60 W) and 2126.0 ± 1.4 µm (120 W). At the same time, the extent of the coagulation zone decreased with a consistent speed: 221.8 ± 2.9 µm (20 W), 324.9 ± 1.8 µm (60 W), and 450.5 ± 1.8 µm (120 W). With a consistent laser energy and increasing speed, we also saw a decrease in the size of the vaporization and of the coagulation zone. The same applies for an increasing distance of the bare fiber to the lung surface. The coagulation effect is the dominant effect here. At an operating speed of 5 mm/s and a maximum laser energy of 120, the 600 µm bare fiber exerts a maximum effect. With an increasing distance of the tip of the bare fiber to the lung surface, the coagulation effect is dominant. The effect of the laser decreases with increasing operating speeds.
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