Identification of the intersegmental plane by arterial ligation method during thoracoscopic segmentectomy

Pulmonary lobectomy is the standard surgical procedure for early-stage lung cancer, further supported in 1995 by the Lung Cancer Study Group’s randomized trial [11]. Recently, several studies have demonstrated that segmentectomy can achieve equivalent short-term surgical results and long-term oncological outcomes for patients with early-stage NSCLC compared to lobectomy [4, 5, 12]. Furthermore, compared with lobectomy, segmentectomy offers the advantage of preserving whole lung function [13, 14]. Therefore, segmentectomy is not only a reasonable choice for patients with poor lung function but also a curative surgery for patients with stage IA lung cancer. However, segmentectomy is considered technically challenging, preventing its widespread application.

Determining the intersegmental plane is one of the most critical steps of segmentectomy. Inaccurate identification of the intersegmental plane may lead to excessive resection of the parenchyma, insufficient surgical margin, and even residue of the lesions. This condition can also increase postoperative complications, such as air leakage, atelectasis, and hemoptysis. Therefore, several techniques have been proposed to identify the intersegmental plane accurately [8, 15,16,17,18,19,20].

The conventional inflation-deflation technique identifies the intersegmental plane by inflating the target segment and deflating the preserved segment, with the disadvantage of limiting the thoracic operating space. Therefore, the modified inflation-deflation technique was more commonly used [15]. However, the inflation-deflation line may be unclear and inaccurate because of the collateral ventilation via the Kohn pores, the Lambert canals, and the direct airway anastomosis [7]. Alternatively, the resected segment inflation technique can be used to determine intersegmental planes, which selectively inflates the target segment through bronchial jet ventilation [16], air injection into the target bronchus using a butterfly needle [17], or bronchial ligation with a slip knot before whole lung deflation [18]. Due to collateral ventilation, these methods share the same potential limitation of inaccurate intersegmental planes. The staining technique by bronchial injection of dyes, such as methylene blue or ICG, has also been used to identify intersegmental planes [19, 20]. This method can not only make the intersegmental line appear on the lung surface but also make the lung parenchyma of the target segment stained. However, a potential problem with this approach is that the dye can spread into adjacent segments through the Kohn pores.

The near-infrared fluorescence mapping with intravenous ICG has become an innovative technique, which can provide a clear view of the segment borders [8, 21]. This method is based on differential blood flow between the resected segment and the residual segment caused by the severing of the target segmental artery. The advantage of the ICG fluorescence method is that it does not require intraoperative lung re-inflation and thereby doesn’t affect maneuver space during video-assisted thoracic surgery. Additionally, another diffusion-based method is the arterial-ligation technique proposed by Iwata et al. [9], in which only the pulmonary artery was ligated before lung inflation, without ligation of the bronchus and the vein. Recently, Fu et al. [10] showed that the arterial-ligation method is feasible and effective in identifying the intersegmental plan compared to the modified inflation-deflation method. To further validate the feasibility and effectiveness, we compared the arterial ligation method with the ICG fluorescence method. Our results suggested that the intersegmental plane determined by the arterial ligation method is comparable to the ICG fluorescence method. Moreover, we found that this approach is helpful for subsegmental resection and combined subsegmental resections, as shown in others [9, 10, 22]. Notably, the arterial ligation method is much more convenient than those above. However, it takes a longer time to wait for the appearance of the intersegmental plane compared to the ICG fluorescence method. The major problem with the arterial ligation method is difficulty determining the intersegmental plane in patients with severe emphysema [10]. In our study, the intersegmental planes were successfully identified in all patients, as none of the included patients had severe emphysema.

The mechanism for identifying the intersegmental plane using this method was explained by Iwata et al. [9] from the perspective of gas exchange. The oxygen in the alveoli of the resected segment cannot enter the bloodstream through the gas exchange because of arterial ligation. In contrast, the oxygen in the residual segments can be taken away by blood flow. Thus, an inflation-deflation line appears between the resected segment and residual segments. Based on this theoretical basis, we can speculate that severing both the arteries and veins of the target segment would be more favorable for the appearance of the inflation-deflation line. In the study by Fu and colleagues [10], it was shown that the waiting time for the arterial ligation method was a little longer than that for the inflation-deflation technique. However, this mechanism has not been experimentally confirmed. If this is true, the waiting time for the appearance of the intersegmental plane will vary when the lung is inflated with different gases, which needs to be verified in future studies.

In conclusion, the arterial ligation method can accurately identify the intersegmental plane during the segmentectomy, a simple and effective alternative to other methods. However, the underlying mechanism remains to be further experimentally confirmed.

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