With the wide application of high-resolution thin-slice CT examination, more and more pulmonary nodules have been found, including early NSCLC. Studies confirm that IA stage NSCLC has the similar long-term survival rates of lobectomy and thoracoscopic anatomical segmentectomy [1–3]. Segmental lung resection has the advantages of preserving more normal lung tissue and causing less trauma. Therefore, segmental lung resection is not only a reasonable choice for patients with poor lung functionbut also an effective surgical method for patients with stage IA lung cancer. However, thoracoscopic assisted segmental lung resection presents some technical challenges, among which the determination of the intersegmental plane is one of the most complex operations. On one hand, inaccurate determination of the intersegmental plane may lead to insufficient resection scope, resulting in residual lung tissue of the target segment, inadequate resection margin, and even residual lesions. On the other hand, excessive resection scope may lead to unnecessary resection of normal lung tissue. At the same time, the inaccurate determination of the intersegmental plane can also lead to the injury of the intersegmental vein, air leakage, poor lung inflation, and other problems. Therefore, the determination of intersegmental plane is the key step of anatomic segmental lung resection.
There are several methods used to determine the intersegmental plane[5]. Bronchial occlusion and vascular occlusion are the two main methods. The most commonly used bronchial method is the dilatation and collapse method, which is to cut off the target bronchi and dilate the lung, so that the remaining lung expands and the target lung collapses to determine the intersegmental plane. However, the presence of Kohn holes causes the target lung to expand along with the remaining lung. As a result, this method is inadequate in determining the intersegmental plane accurately. At present, the improved dilatation collapse method is more commonly used. After the target bronchus was cut off, the whole lung was inflated by double-lung ventilation, and then the whole lung was inflated by single-lung ventilation. When the remaining lungs collapsed naturally while the target lung was still inflated, the intersegmental plane could be presented. In addition, we can also reserve a slide node on the target segment bronchiand ligature the bronchi after the whole lung expands, and wait for the appearance of the dilatation-collapse interface between the target segment and the remaining lungs[6]. Furthermore, the intersegmental plane can also be determined by selective bronchial ventilation through the target segment, such as inserting butterfly needle into the target segment bronchus and ventilating into it[7], and positioning bronchoscope to the target segment bronchus for high-frequency ventilation[8]. All of the above methods are based on the bronchial ventilation. Due to the influence of Kohn hole, the appearance of intersegmental plane is not accurate enough, and the operation of selective bronchial ventilation method is complicated. Still, there are bronchial dye injection methods, such as ICG[9], methylene blue and so on. But the operation is also complex, and the fluorescent dyes need special equipment and are difficult to use. Based on the pulmonary circulation, the pulmonary artery of the target segment is severed in advance, and then ICG is injected via peripheral vein. After a few seconds, the lung tissues outside the target segment show green fluorescence, and the intersegmental plane is clearly visible. However, the duration of the appearance of the intersegmental plane is relatively short. In addition, patients who smoke heavily may have poor visibility in the intersegmental plane after ICG injection[10].
The arterial ligation method is also based on pulmonary circulation. this method was first reported by Iwata in 2013[11]. It is speculated that the principle of intersegmental plane presentation is as follows: when the target segment artery is blocked, pure oxygen is used to dilate the lung. And single lung ventilation is performed again. The oxygen in the lung tissues of the target segment cannot be taken away by the blood in the pulmonary circulation and the tissues continue to expand, and the rest of lungs collapse, resulting in the intersegmental plane (Fig. 1a). Therefore, we hypothesized that simultaneous dissection of the target artery and vein might be more effective[12]. Recently, Fu et al.[13] confirmed the feasibility of this method through more cases. This method is in good agreement with the intersegmental plane determined by bronchial occlusion and vascular occlusion. Considering that both the arterial ligation method and ICG method are based on the principle of pulmonary circulation, we compared the intersegmental planes determined by the two methods. And the results showed that the two methods are highly consistent. In the traditional improved dilatation and collapse method, the bronchus, arteries and veins are separated in advance. Therefore, it is reasonable to speculate that the appearance of intersegmental plane in the improved dilatation and collapse method is also due to pulmonary circulation, rather than the principle of bronchial ventilation alone. Of course, this hypothesis needs further testing. The advantages of the arterial ligation method are that it is simpler than the traditional improved dilatation and collapse method, that the intersegmental plane is more durable than the ICG method, and that no special equipment is required.
Admittedly, there are shortcomings in this study. First, only common lung segments were selected in the study with a small number of cases. Secondly, the effectiveness of this method in patients with COPD needs further validation. Finally, as the traditional dilatation and collapse method, the arterial ligation method also requires the intraoperative cooperation of the anesthesiologist.
In conclusion, the arterial ligation method can successfully identify the intersegmental plane, and it results are consistent with the that of the ICG method. And the arterial ligation method is simpler than other methods. Therefore, it is worth popularizing and applying. The principle of arterial dissection may be that oxygen in alveoli cannot disperse into blood after the pulmonary circulation in target tissues is interrupted, which needs further study to clarify.