FormalPara Key Summary Points

The relative merits of thoracoscopy-guided thoracic paravertebral block (TTPB) and ultrasound-guided thoracic paravertebral block (UTPB) remain unclear

We compared the application of TTPB and UTPB in terms of surgical difficulty of the block, success rate, and analgesic effect after thoracoscopic lung cancer radical surgery

When compared with UTPB, TTPB is simpler and more convenient, takes less time, has a higher success rate of the first puncture, wider block segments, and a better analgesic effect

TTPB can effectively reduce the pain after thoracoscopic radical resection in lung cancer

Introduction

Compared with traditional open thoracotomy, thoracoscopic minimally invasive surgery has many advantages. It requires a small incision, causes minimal trauma and less pain, and allows faster recovery [1]. Therefore, thoracoscopic minimally invasive surgery has become the main surgical approach for thoracic surgery [2]. Postoperative pain in thoracic surgery is primarily due to chest wall incision and catheter stimulation. Even though thoracoscopic minimally invasive surgery has alleviated surgical trauma and pain, postoperative pain is severe, which increases postoperative complications and even affects postoperative recovery [3].

Owing to the advancement and popularization of ultrasound visualization technology, the application of ultrasound-guided thoracic paravertebral block (UTPB) in postoperative analgesia after thoracic surgery has garnered considerable attention [4, 5]. Thoracic paravertebral block (TPB) is a technique used to make percutaneous puncture to inject local anesthetics (LAs) into the paravertebral space, producing an effect similar to unilateral epidural block [6, 7]. Nevertheless, UTPB has limited surgical space and requires high blocking techniques, which reduces the success rate. In previous studies, researchers have confirmed a novel technique for TPB, named thoracoscopy-guided thoracic paravertebral block (TTPB) (Fig. 1) [8, 9]. This technique is easy to perform and can effectively reduce postoperative pain.

Fig. 1
figure 1

Range of action of the TTPB in the horizontal plane. The brown area represents paravertebral space and spread range of the LAs. The arrow indicates the site and direction of the thoracic paravertebral block for needle insertion [9]

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However, no comparative study has been performed on the application of TTPB and UTPB in postoperative analgesia in thoracic surgery. Hence, in this study, we aim to compare the application of TTPB and UTPB in terms of surgical simplicity, surgical time, success rate of the first puncture, and analgesic effect after thoracoscopic lung cancer radical surgery.

Methods

Study Design and Population

This is a single-center, prospective, single-blind, randomized, clinical trial. The study obtained approval from the Ethics Committee of the Lihuili Hospital Affiliated of Ningbo University (Approval No. KY2021PJ002). This study is registered with the Chinese Clinical Trial Registry (ChiCTR2300072005). The date of first registration is 31 May 2023. This study was performed in accordance with the Helsinki Declaration of 1964 and its later amendments. Study methods and results reported in adherence to the Consolidated Standards of Reporting Trials (CONSORT) statement. In total, 80 patients undergoing thoracoscopic radical surgery for lung cancer were enrolled between June 2023 and September 2023 at the affiliated Lihuili Hospital of Ningbo University. Informed consent was obtained from all patients. The inclusion criteria for patients were as follows: aged between 20 and 70 years, American Society of Anesthesiologists physical status grade I–III, and scheduled to undergo thoracoscopic radical surgery for lung cancer. The exclusion criteria were as follows: patient refusal of thoracoscopic surgery; abnormal coagulation functions; history of spinal deformities, fractures, trauma, surgery, or thoracic aortic aneurysm; severe pleural adhesions; unplanned second surgery after surgery; allergies to LAs; intraoperative pathological confirmation of benign or in situ tumor; failure to achieve proper block; mismatched criteria; or requested withdrawal during the study. The surgery and anesthesia procedures were performed by the same experienced team.

Randomization and Blinding

Participants were randomly divided into the TTPB group and UTPB group in a ratio of 1:1. Randomization sequences were generated by a computer, and the sequences were hidden in opaque sealed envelopes. A dedicated nurse informed the anesthesiologist and surgeon of the grouping results. Anesthesiologists or surgeons performed UTPB or TTPB according to the patients’ group. The nurses, surgeons, and anesthesiologists did not participate in the follow-up, data collection, or analysis. Patients and other investigators were blinded to the grouping.

Anesthesia Procedure

All patients received total intravenous anesthesia. Rapid intravenous anesthesia was induced with 0.05 mg/kg midazolam, 0.3 μg/kg sufentanil, 1.5–2 mg/kg propofol, and 0.9 mg/kg rocuronium. After oral tracheal intubation, the bronchial occlusive catheter was inserted and positioned using a fiberoptic bronchoscope. The ventilator was connected to supply intermittent positive pressure ventilation, with tidal volumes of 8 mL/kg during two-lung ventilation and 6 mL/kg during one-lung ventilation. The respiratory rate was set at 10–12 times/min and the pressure was maintained at the end-expiratory carbon dioxide (PETCO2) between 35 and 40 cmH2O during the surgery. The intraoperative anesthesia was maintained at 6–8 mg kg−1 h−1 propofol, 0.1–0.3 μg kg−1 min−1 remifentanil via micropump injection, and 0.15 mg per kg body weight (kg·0.5 h) rocuronium via a single injection.

Surgical Procedure

The patient underwent a three-port thoracoscopic radical resection of lung cancer via lobectomy or segmental resection. The surgical incisions were made in the fourth intercostal space between the midline of the clavicle and the anterior axillary line, the seventh intercostal space of the middle axillary line, and the seventh intercostal space between the line of the subscapular angle and the posterior axillary line. Following the pathological confirmation of a malignant tumor during surgery, lymph node dissection was performed on the hilum of the lung. A No. 26 drainage tube was routinely placed post surgery.

Analgesia Methods

Before the chest was closed, the injection needle with an extension tube was vertically inserted into the parietal pleura between the fifth and sixth thoracic vertebrae and 1 cm beside the vertebrae through the chest cavity under the direct visual guidance of thoracoscopy, with a depth of approximately 0.5 cm under parietal pleura in the TTPB group. Subsequently, 20 mL of 0.375% ropivacaine was injected (Fig. 2) [8, 9]. The TTPB surgery was performed by the surgeon.

Fig. 2
figure 2

TTPB between the fifth and sixth thoracic vertebrae. The white raised area indicates the diffusion of local anesthetics in the paravertebral space. The black solid line represents the thoracic vertebrae, and the black dashed line represents the intercostal space

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Patients in the UTPB group were positioned laterally at the end of surgery. A 5–2 MHz lower frequency convex probe (Sonosite rC60x, FUJIFILM Sonosite, Bothell, WA, USA) was positioned parallel to the fifth intercostal space to view the transverse process and paravertebral space. A 22-gauge needle (80 mm, Stimuplex D, B. Braun, Germany) was inserted using the in-plane technique. Once the needle reached the paravertebral space, 3 mL of normal saline was first injected. When the downward displacement of the parietal pleura was observed, 20 mL of 0.375% ropivacaine was injected into the paravertebral space [10]. The UTPB surgery was performed by the anesthesiologist.

Towards the end of the surgery, all patients of the two groups were connected to a patient-controlled intravenous analgesia (PCIA) pump, which supplied sufentanil at a dose of 1.5 μg kg−1 (diluted to 100 mL with normal saline). The parameters were set as a continuous dose of 2 mL/h, a bolus dose of 1.5 mL, and a locking time of 15 min. When the VAS score was greater than five or the pain became intolerable, 40 mg of parecoxib was injected intramuscularly.

Data Collection

Primary outcomes

The primary outcomes were the surgical time of TPB and the success rate of the first puncture. The surgical time for a block in the UTPB group was considered from the placement of the ultrasound probe on the chest wall to the completion of the drug injection. The surgical time for the block of the TTPB group started when the needle holder entered the chest cavity and the medication injection was completed. The first needle that directly reached the paravertebral space was considered the success of the first puncture.

Secondary Outcomes

The range of blocked segments was determined using acupuncture 2 h post operation. The VAS scores (rest and coughing) at 2, 6, 12, 24, and 48 h post operation were found. The incidence of postoperative adverse reactions, such as bilateral block, nausea, vomiting, drowsiness, respiratory depression, and atelectasis, were recorded.

Sample Size

Pilot testing indicated that the success rate of the first puncture was 80% in the UTPB group and 100% in the TTPB group. Using the MedSci Sample Size Tools at a power of 0.8 with 0.05 alpha, we found that 35 patients were required in each group. Therefore, considering a potential 10% rate of missing data or dropouts, 40 patients were included in each group.

Statistical Analysis

Data were analyzed using the SPSS version 23.0 software (IBM Corp. Armonk, NY, USA). Continuous variables conforming to normal distribution are expressed as mean ± standard deviation. The differences between the two groups were determined using Student’s t test. For the intragroup comparison of data, a repeated-measures analysis was performed. Variables with a skewed distribution are presented as medians (quartiles) and were compared using the Kruskal–Wallis H test. Categorical data are presented as numbers (percentages). Differences in the categorical data between the two groups were determined using Fisher’s exact test or the chi-square (χ2) test. A P value of less than 0.05 was considered statistically significant.

Results

Baseline Characteristics and Perioperative Details of Patients

In total, 80 patients were included in this study and randomly divided into the TTPB and UTPB groups. One patient in the UTPB group was confirmed to have a benign tumor via intraoperative pathology, whereas one patient in the TTPB group had severe thoracic adhesions during surgery. Therefore, these two patients were excluded from the study. Thus, 78 patients were finally included in the study, and the surgery and research process were successfully performed, as shown in the CONSORT flow diagram (Fig. 3). No significant difference was found in terms of the baseline characteristics and perioperative details between the two groups (P > 0.05, Table 1).

Fig. 3
figure 3

CONSORT flow diagram for the trial

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Table 1 Comparison of baseline characteristics and perioperative details between two groups
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Primary Outcomes

The surgical time of TPB in the TTPB group was significantly shorter than that in the UTPB group (2.2 ± 0.3 vs. 5.7 ± 1.7 min, t = − 12.411, P < 0.001).

There were nine patients in the UTPB group in whom the anesthesiologist failed to reach the paravertebral space during the first puncture and needed to adjust the needle direction and angle twice or multiple times. The success rate of the first puncture was 76.9%, which was significantly lower than that of the TTPB group’s 100% (χ2 = 8.309, P < 0.001).

Secondary Outcomes

The TTPB group showed a significantly larger sensory block segment than the UTPB group (6.5 ± 1.2 vs. 5.1 ± 1.3 levels, t = − 5.306, P < 0.001).

The VAS scores during rest and coughing at 12 h, 24 h, and 48 h were significantly higher than those at 2 h and 6 h post operation in the UTPB group (P < 0.001). The VAS scores during rest and coughing at 48 h post operation were significantly higher than those at 2 h, 6 h, 12 h, and 24 h post operation in the TTPB group (P < 0.001). The VAS scores were significantly lower during rest and coughing at 12 h and 24 h post operation in the TTPB group than in the UTPB group (rest: 2.5 ± 0.4 vs. 3.4 ± 0.6, t = 7.325, P < 0.001; 2.5 ± 0.5 vs. 3.5 ± 0.6, t = 7.885, P < 0.001; coughing: 3.4 ± 0.6 vs. 4.2 ± 0.7, t = 5.057, P < 0.001; 3.4 ± 0.6 vs. 4.2 ± 0.8, t = 4.625, P < 0.001, respectively). No significant difference was found in VAS scores during rest and coughing between the two groups at 2 h, 6 h, and 48 h post operation (P > 0.05, Table 2).

Table 2 Comparison of VAS scores between two groups
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Both groups of patients did not show bilateral block. No significant difference was found in terms of adverse reactions, such as bilateral block, nausea, vomiting, drowsiness, respiratory depression, and atelectasis, between the two groups (P > 0.05, Table 3).

Table 3 Comparison of adverse reactions after surgery between two groups
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Discussion

The popularization of the fast-track surgery concept and the advancements in minimally invasive technology have established thoracoscopic minimally invasive surgery as the primary approach in thoracic surgery [11]. Although thoracoscopic minimally invasive surgery reduces surgical trauma, patients still experience severe postoperative pain, which seriously affects postoperative recovery [3]. Thoracic surgery, including various degrees of lobectomy, contributes to a decrease in postoperative lung function reserve in patients. Additionally, the presence of severe postoperative pain often discourages patients from taking deep breaths and actively coughing. These factors can collectively contribute to postoperative pulmonary complications [12]. Implementing comprehensive postoperative analgesia is beneficial for patients as it allows them to cough and expel phlegm at an early stage. It also improves lung function, reduces the occurrence of postoperative pulmonary complications, and supports overall postoperative recovery [13,14,15].

Recently, with the continuous advancements in ultrasound imaging technology and the promotion of ultrasound visualization in the perioperative period, UTPB has become a primary approach for postoperative analgesia in thoracic surgery [5]. The thoracic paravertebral space, resembling a wedge-shaped structure in the horizontal plane, encompasses the spinal nerve, intercostal nerve, and sympathetic nerve chain within the intervertebral foramen. UTPB involves percutaneous puncture under ultrasound guidance, with LAs injected into the thoracic paravertebral space. The LAs not only diffuse horizontally at the injection site but also diffuse into multiple segments both upward and downward in three-dimensional space. Consequently, they can simultaneously block nerves in multiple segments of the paravertebral space, producing an effect similar to unilateral epidural block. This effectively reduces postoperative incision pain, catheter irritation pain, and visceral pain [16]. TPB can also prevent hypotension due to thoracic epidural analgesia, which is increasingly used in clinical practice [6, 17]. However, UTPB demands proficiency in ultrasound application and block technology and is susceptible to obstruction by bony structures such as transverse processes and the scapula, which limits surgical space and reduces the success rate.

In previous studies, researchers have verified a novel technique for TPB, known as TTPB [8, 9, 18]. This technique involves a complete exposure of the thoracic vertebrae, paravertebral space, and intercostal space under the field of thoracoscopy. LAs are directly injected into the paravertebral space beneath the parietal pleura under thoracoscopic guidance. This approach allows for the visualization of LA diffusing in the paravertebral space across multiple segments above and below the injection site. Previous studies have confirmed the efficacy and safety of TTPB. TTPB is simple and convenient, which can effectively reduce the postoperative pain of esophageal cancer and promote postoperative recovery [8]. In another study, researchers found that combining TTPB with PCIA can effectively alleviate postoperative pain, reduce adverse reactions, and promote postoperative recovery in patients undergoing single-port thoracoscopic wedge resection of the lung [9]. The TTPB procedure is simple, and LAs can be visualized while they are injected into the thoracic paravertebral space and spread in multiple spaces. As a relatively new TPB technique, it is unclear whether it is different from the commonly used UTPB in terms of analgesic effects. Therefore, we aimed to compare these two types of thoracic paravertebral block techniques in terms of block success rate, surgical time, block efficacy, and scope. We provide a comprehensive basis for TTPB in postoperative analgesia of thoracic surgery.

The success rate of the block is a crucial factor affecting its effectiveness and can be affected by various factors such as block difficulty, technical proficiency, surgical space, and imaging level [19]. In this study, there were nine patients in the UTPB group in whom the anesthesiologist failed to reach the paravertebral space during the first puncture and required adjustments to the needle direction and angle two or multiple times. The success rate of the first puncture was 70%, which was significantly lower than the 100% observed in the TTPB group. This can be attributed to the need for the puncture needle to avoid bone structures, such as transverse or articular processes under the ultrasound field, to reach or approach the paravertebral space [20]. Additionally, the inner edge of the scapula obstructs the puncture needle, resulting in a narrow puncture space. UTPB also has high requirements for ultrasound imaging and ultrasound-guided puncture techniques, especially in the case of obesity. These factors contribute to a reduced success rate of the first puncture in UTPB reaching the thoracic paravertebral space [16]. The success rate of the selected experienced doctors implementing the procedure was 70% in this study; the success rate might therefore be lower if doctors are not proficient enough. The thoracic paravertebral space is completely exposed during thoracoscopy. The puncture needle is guided by thoracoscopy through an intrathoracic approach, passing through the parietal pleura to reach the thoracic paravertebral space. The TTPB procedure is extremely simple and convenient, not limited by the proficiency of operators or imaging conditions, resulting in a 100% success rate.

In this study, the time required for TPB was significantly shorter for the TTPB group than the UTPB group, indicating that TTPB procedures are simpler and more convenient. Several primary reasons contribute to this difference. Firstly, the thoracic paravertebral space is completely exposed during thoracoscopy, allowing the puncture needle to rapidly reach the blocking site without the requirement for additional disinfection and sterile drapes, thereby saving a lot of time. Secondly, factors affecting the success rate of UTPB, as discussed earlier, also lead to longer block surgical times. Additionally, some patients may require two or more needle injections to reach the paravertebral space, further increasing the surgical time. Thirdly, sufficient time is required to completely expose the thoracic paravertebral space and form a clear puncture path under ultrasound guidance, particularly in the case of patients with obesity. The timing for the UTPB group in this study started with the placement of the ultrasound probe on the chest wall. If the total blocking surgical time was combined with the disinfection of the puncture site, laying sterile wipes, and applying sterile covers on the ultrasound probe, the time would be longer. This further indicates the simplicity and convenience of the TTPB procedure.

The blocking range of TPB typically spans approximately 4–8 segments and is influenced by factors such as the volume of LAs and the accurate injection of LAs into the thoracic paravertebral space [21, 22]. In this study, the block range in the UTPB group was 5.1 ± 1.3 levels, which is consistent with the results of previous studies [7, 23]. However, the block range was significantly larger in the TTPB group than in the UTPB group. This difference may occur because TTPB can ensure the accurate injection of all LAs into the thoracic paravertebral space. Under thoracoscopy, the effective diffusion of the drug solution in the paravertebral space of multiple segments can be viewed. The primary way to confirm the success of UTPB is to move the pleura downward during injection. However, as a result of limitations in ultrasound technology, operator ultrasound skills, and blocking techniques, the puncture needle tip in UTPB may reach only the lateral paravertebral space or even the more lateral intercostal space. Although the observation of pleural downward movement may still occur, LAs might spread more into the intercostal space, resulting in an insufficient effective volume of the drug solution injected into the thoracic paravertebral space. Therefore, this can lead to a smaller effective plane of UTPB.

Many studies have reported that the duration of a single injection of TPB is 6–12 h [7, 23, 24]. The VAS scores of the UTPB group at 12 h, 24 h, and 48 h post surgery were significantly higher than those at 2 h and 6 h after the surgery. This suggests that the time effect of UTPB lasts more than 6 h, but less than 12 h, which is consistent with the results of previous studies [24]. The VAS score was significantly higher at 48 h post surgery than at other time points in the TTPB group. Furthermore, the VAS scores were significantly lower at 12 h and 24 h post surgery in the TTPB group than in the UTPB group. This indicates that the blocking effect of TTPB persists 12 h after surgery, indicating that the time effect of TTPB may exceed 12 h, possibly reaching 24 h, which is consistent with previous studies [8, 9]. This can occur because thoracoscopy ensures that LAs are completely injected into the paravertebral space and they are absorbed slowly. However, UTPB can inject part of the drug solution into the intercostal space only by pleural downward movement, which cannot ensure that all LAs are injected into the paravertebral space. Therefore, LAs in the paravertebral space are absorbed faster and the blocking effect is shorter.

The absence of significant differences in postoperative adverse reactions between the two groups suggests that TTPB is a safer procedure. The inner side of the thoracic paravertebral space is connected to the spinal canal through the intervertebral foramen, allowing LAs to spread into the spinal canal and result in an epidural block. Particularly, local anesthetics can be effectively injected into the thoracic paravertebral region during TTPB, with a higher possibility of the intraspinal block. However, no epidural block was observed in this study, further suggesting that TTPB has high safety.

This study has many limitations that should be addressed. We only observed the pain score at several fixed postoperative time points, without conducting a comprehensive and comparative examination of the duration of the two types of TPB techniques. Additionally, we only used needle prick pain sensation to judge the block range and did not use imaging methods to observe the diffusion of LAs in the thoracic paravertebral space from the three-dimensional levels. Currently, the research on TTPB primarily focuses on its analgesic effects, with limited exploration into the underlying principles of the block or the diffusion range of LAs. Therefore, in future studies, we aim to determine the mechanism of TTPB from a three-dimensional perspective through staining or contrast agents.

Conclusions

When compared with UTPB, TTPB is simpler and more convenient, takes less time, achieves a higher success rate on the first puncture, affects wider block segments, and has a longer action time. Therefore, it can be used to alleviate pain after thoracoscopic lung cancer radical surgery.