Comparison of local tissue damage: monopolar cutter versus Nd:YAG laser for lung parenchyma resection. An experimental study.

Objectives: Lung metastases are non-anatomically resected while sparing as much parenchyma as possible. For this purpose, a few surgeons use the Nd:YAG Laser LIMAX 120, whereas the majority of surgeons use a monopolar cutter like the MAXIUM. The aim of this experimental study was to investigate which instrument causes less lung-tissue damage at the same power output.

Methods: These experiments were conducted on left lungs (n = 6) taken from freshly slaughtered pigs. The laser and the monopolar cutter were fixed in a hydraulic mover. The laser was focused at a distance of 3 cm to the lung tissue and the monopolar cutter was fixed in pressure-free contact with the lung surface. Both instruments were manoeuvred at a speed of 5, 10 and 20 mm/s in a straight line at an output of 100 watts over the lung surface. The lung lesions that ensued were then examined macro- and microscopically. The same procedures were repeated at a distance of 1 cm creating parallel lesions in order to analyse the lung tissue in between the lesions for thermal damage. In addition, two implanted capsules in the lung tissue simulating a lung nodule were resected with either the laser or the monopolar cutter. The resection surfaces were then examined by magnetic resonance imaging and histology for tissue damage. Finally, we created a 2-cm wide mark on the lung surface to test the resection capacity of both instruments within 1 min.

Results: The laser created sharply delineated lesions with a vaporization and coagulation zone without thermal damage of the surrounding lung tissue. With lowering the working speed, each zone was extended. At a working speed of 10 mm/s, the mean vaporization depth using the laser was 1.74 ± 0.1 mm and the mean coagulation depth was 1.55 ± 0.09 mm. At the same working speed, the monopolar cutter demonstrated a greater cutting effect (mean vaporization depth 2.7 ± 0.11 mm; P < 0.001) without leaving much coagulation on the resection surface (mean coagulation depth 1.25 ± 0.1 mm; P = 0.002). In contrast to the laser, the monopolar cutter caused thermal damage of the adjacent lung tissue. The adjacent tissue injury was detected in histological examination as well as in the MRI findings. Adjacent lung tissue after lung metastasectomy using the monopolar cutter was hyper-intensive in T2-weighted MR imaging, indicating a severe tissue damage. No significant changes in signal intensity were observed in T2-weighted imaging of the adjacent lung tissue after using the laser for lung resection. One minute of laser applied at a 100-watt output penetrated a lung surface area of 3.8 ± 0.4 cm(2) compared with 4.8 ± 0.6 cm(2) of surface after application of the monopolar cutter (P = 0.001).

Conclusions: The monopolar cutter possesses indeed a greater cutting capacity than the laser, but it also causes more adjacent tissue injury. Thus, laser resection might be preferred for lung metastasectomy.