Comparison of the local effects of a 600-μm bare fibre at high laser power on lung parenchyma: Nd:YAG laser 1320 vs. 1064 nm.

Lung metastases are often resected non-anatomically with a laser using a diode-pumped Nd:YAG laser at a wavelength of 1320 nm with a laser output of up to 60 W. Usually the removal of lesions is carried out in contact mode by means of a bare fibre. We compared the local effects of an Nd:YAG laser at a wavelength of 1064 nm with those at a wavelength of 1320 nm using a 600-μm bare fibre in contact mode in an experimental model. The investigations were carried out on porcine lungs freshly withdrawn at the abattoir. The 600-μm laser fibre was fixed vertically in contact with the lung surface on a fibre holder. The fibre holder was connected to a feeding device that advances the laser fibre at constant speeds (5, 10 or 20 mm/s). In each case, two laser powers were examined: 20 and 60 W. The lung lesions produced by the laser fibre were excised for histological examination. After haematoxylin-eosin staining, the depth of the vaporisation and coagulation zones (in μm) from the laser cuts was measured. For each setting, an average value was calculated. The individual groups were compared for significance using a non-parametric Mann-Whitney U test (p < 0.05). At a low speed of the bare fibre of 5 mm/s and a laser output of 20 W, the average depth of the vaporisation zone was 858 ± 3.3 μm (λ = 1064 nm) compared to 766.0 ± 7.5 μm (λ = 1320 nm) (p < 0.01). Upon faster movement (20 mm/s), the extension of the vaporisation zone decreased to 320.3 ± 7.1 μm (λ = 1064 nm). The depth of the vaporisation zone increased significantly at 60 W, both at λ = 1064 and 1320 nm with 1517.0 ± 1.7 μm and 1414.0 ± 4.9 μm, respectively. The extent of the coagulation zone was significantly smaller at 20 W and the low speed of 5 mm/s, namely, 200.4 ± 3.7 μm (λ = 1064 nm) and 224.1 ± 2.8 μm (1320-nm laser). Upon faster movement of the laser fibre at the same output, the extent of the coagulation zone decreased in both groups. At a laser power of 60 W, the extent of the coagulation zone was significantly less with the 1064-nm laser (110.3 ± 2.4 μm) than with the 1320-nm laser (324.8 ± 1.9 μm; p < 0.001). When the laser fibre moves more rapidly, the extent of the coagulation zone decreases further. The Nd:YAG laser with a wavelength of 1320 nm still has the optimal ratio of cutting and coagulation capacity on the resection surface. With the 1064-nm Nd:YAG laser, a higher cutting capacity is associated with a decrease of the coagulation capacity.