TSNB has been widely used over the past decades as an anesthetic technique, not only to prevent persistent postoperative pain after thoracic surgery, but also to treat neuropathic pain disorders, such as complex regional pain syndrome, phantom limb pain, post-herpetic neuralgia, and ischemic vascular disease14,15,16,17. In recent studies, the role of TSNB has expanded to include different purposes other than pain practice. As an example, it can be applied to improve coronary microcirculation in rats with chronic heart failure. Sun and his colleagues reported that high thoracic sympathetic block improved myocardial capillary spasm and growth18. TSNB can also be applied as a predictive procedure for compensatory hyperhidrosis before sympathectomy in primary hyperhidrosis, based on the effect of sympathetic block on increasing skin perfusion and temperature through vasodilation at the anesthetized sites10,11,19,20. Miller et al.10 performed a temporary TSNB in 25 patients to predict whether compensatory hyperhidrosis would occur after sympathectomy in primary hyperhidrosis. All patients had temporary relief of primary hyperhidrosis after TSNB. Three patients had temporary compensatory hyperhidrosis after TSNB, and one of them experienced severe compensatory hyperhidrosis and did not proceed with sympathectomy. The remaining two patients experienced mild compensatory hyperhidrosis after TSNB and also had it after sympathectomy. Their results showed that temporary TSNB is a reversible and accurate procedure for determining compensatory hyperhidrosis after sympathectomy.
Over the past decades, there have been several approaches to blocking thoracic sympathetic nerve: the landmark-based approach, US-guided approach, CT-guided approach, fluoroscopically, and thoracoscopically10,11,12,13,21,22,23. A classic technique that does not use image guidance is a landmark-based approach that elicits a loss of resistance21. Other techniques include simple advancement over or under transverse process for 1 to 1.5 cm, using a nerve stimulator, pressure monitoring and X-ray direct vision24,25,26,27. Research examining a landmark-based approach TSNB found that the failure rate varies from 6.8 to 10%28,29,30. Like the landmark-based approach with the aid of X ray direct vision, TSNB can be conducted under imaging guidance, such as US-guidance, CT-guidance, and under fluoroscopy12,22,23. TSNB under fluoroscopy and the CT-guided approach results in inevitable radiation exposure and uncomfortable posture of the operator and patient during the procedures12. In addition, TSNB with the CT-guided approach is not practical in clinical practice. Under fluoroscopy, TSNB can be done by detecting bony surfaces as landmarks for introducing the needle for block; however, other structures such as vascular and soft tissue structures cannot be seen, which increase the risk of injuries of adjacent structures. Kim and his colleagues have reported that most patients (80%) achieved a temperature increase (≥ 1.5 °C) on the palm after TSNB under fluoroscopy at the T2 spinal level, which was superior to TSNB under the US-guided approach (20.0%)31. On the other hand, the US-guided approach is preferable over the previously mentioned approaches for checking the surrounding structures, including vascular and soft tissue structures, in detail to reduce complications32,33. A recent study by Kim and his colleagues reported that TSNB under the US-guided approach achieved a temperature increase (≥ 1.5 °C) between the ipsilateral and contralateral hands in 7 of 12 patients (58.3%), and minimized complications including pneumothorax12. It is true that the US-guided and CT-guided approaches are less invasive and that US-guided approach can be done at one’s bedside, while TSNB is done under thoracoscopy in the operating room.
From the perspective of accuracy and safety, thoracoscopic TSNB has the advantages of directly targeting the sympathetic nerve in our own eyes, leading to a success rate of approximately 100%10,11. Our results have shown that the mean temperature of the left and right palms following TSNB under thoracoscopy increased more than 1.5 °C in all patients. To further reduce the inconvenience to patients, we share here our experience of TSNB under local anesthesia with a 2-mm single incision not only to reduce invasiveness but also to enhance our accurateness during the surgical procedure. Even though we cannot directly compare our results with those of TSNB using other modalities, direct vision seems to be superior to imaging guidance. Our result has shown that pneumothorax occurred in 6 patients (n = 6/294). However, chest tube catheter drainage was not necessary, because pneumothorax was a result of not completely draining air from the chest cavity after TSNB. Only one patient developed hemothorax after TSNB, which was presumed to have occurred after removal of the trocar from the insertion site of the 2 mm surgical trocar. However, the patient was able to be discharged the next day after small-bore catheter drainage. Temporary ptosis occurred in 10 patients, which is probably caused by the block cranially extending into the sympathetic chain with the mixture injected at the T3 level. Our result has shown that TSNB under thoracoscopy is not inferior to the US-guided approach in terms of complications.
The advantages of thoracoscopic TSNB are the facts that the injection level is accurate, the injection is done under direct vision, and the procedure can be completed before the temperature change of the palm. On the other hand, thoracoscopic TSNB has several disadvantages. First, it is more invasive than the image-assisted procedure, as it requires a tiny skin incision. Second, if there is pleural adhesion, the procedure is difficult. Third, it is difficult for the patient to breathe during the procedure because it is performed under local anesthesia with the lung collapsed. Fourth, complications such as pneumothorax may occur after the procedure due to lung injury caused by thoracoscopic insertion. To predict the effect of sympathectomy for the treatment of hyperhidrosis and the occurrence of compensatory hyperhidrosis, it is recommended to show the same results after the predictive procedure. Therefore, considering the advantages and disadvantages of thoracoscopic TSNB, this modality was used considering accuracy more important than invasiveness to predict compensatory hyperhidrosis before sympathectomy in primary hyperhidrosis. However, if US-guided TSNB is not significantly different from thoracoscopic TSNB in terms of accuracy, it would be better to use US-guided manner.
The limitations of this study are the facts that it was a retrospective study, was conducted at a single institution, was not performed in patients with various diseases, and did not include a comparison with TSNB performed by other modalities. In conclusion, our experiences showed that TSNB using thoracoscopy was accurate, safe and feasible for blocking the thoracic sympathetic nerve in patients with severe primary hyperhidrosis. However, further studies are needed to compare these results with those of TSNB perfomed for other diseases and with the use of other modalities, US-guided or CT-guided manner, in the future.