Transversus Thoracis Muscle Plane Block in Paediatric Patients Who Underwent Minimally Invasive Closure of Transthoracic Ventricular Septal Defect: A Retrospective Study

Objective Minimally invasive closure of transthoracic ventricular septal defect (VSD) has been widely used in paediatric patients. This retrospective study aimed to explore the use of transversus thoracis muscle plane block (TTMPB) in the minimally invasive closure of transthoracic VSD in paediatric patients. Methods From September 28, 2017, to July 25, 2022, a total of 119 paediatric patients scheduled for minimally invasive transthoracic VSD closure were considered for inclusion. Results In total, 110 patients were included in the final analysis. Perioperative fentanyl consumption of the TTMPB group was not different from that of the non-TTMPB group (5.90 ± 1.32 μg/kg vs. 6.25 ± 1.74 μg/kg, p = 0.473). Both the time to extubation and postanesthesia care unit (PACU) stay were significantly shorter in the TTMPB group than in the non-TTMPB group (10.94 ± 10.31 min vs. 35.03 ± 23.52 min for extubation, and 42.55 ± 16.83 min vs. 59.98 ± 27.94 min for PACU stay, both p < 0.001). Furthermore, the postoperative paediatric intensive care unit (PICU) stay in the TTMPB group was significantly shorter than in the non-TTMPB group (1.04 ± 0.28 d vs. 1.34 ± 1.05 d, p = 0.005). Multivariate analysis demonstrated that TTMPB was significantly associated with shorter time to extubation (p < 0.001) and PACU stay (p = 0.001) but not postoperative PICU stay (p = 0.094). Discussion. This study showed that TTMPB was a beneficial and safe regional anaesthesia technique for paediatric patients who underwent minimally invasive closure of transthoracic VSD, although prospective randomized controlled trials are needed to confirm the results.


Introduction
With the development of surgical technology and various devices, minimally invasive closure of the transthoracic ventricular septal defect (VSD) has been widely used in paediatric patients [1,2]. Minimally invasive closure of transthoracic VSD was proven safe with excellent rates of closure [1,3]. Although this surgery procedure leaves a small puncture on the anterior chest wall, postoperative pain management remains a challenge in paediatric patients [4,5].
Pain management plays a critical role in the postoperative recovery of cardiac surgical patients [6]. Opioid-based postoperative pain management is the main strategy for cardiac surgery. However, opioids are associated with some well-known complications like nausea, vomiting, and respiratory depression. Multimodal opioid-sparing approaches, including regional anaesthesia techniques, show benefts and are encouraged [6,7]. Ultrasound-guided transversus thoracis muscle plane block (TTMPB) is a relatively newly developed regional anaesthesia technique [8]. It has shown benefts in open cardiac surgery in paediatric patients [9,10]. However, few studies have explored the efcacy of TTMPB in paediatric patients who underwent minimally invasive closure of the transthoracic VSD.
Terefore, this retrospective study aimed to explore the use of TTMPB in the minimally invasive closure of transthoracic VSD in paediatric patients.

Ethical.
Tis study was approved by the Ethics Committee of the Second Afliated Hospital of the Guangzhou University of Chinese Medicine (chairperson: Prof. Yun Han, approval number: ZF2022-201-01) and was conducted in accordance with the Declaration of Helsinki. Due to the retrospective nature of the study and the use of anonymized data, the requirement for informed consent was waived by the ethics committee. It was registered in the Chinese Clinical Trial Registry at https://www.chictr.org (registration date: July 25, 2022; registration number: ChiCTR2200062147).

Sample Size.
Considering the scarcity of studies on TTMPB in minimally invasive closure of transthoracic VSD and due to the retrospective nature of this study, all paediatric patients scheduled for minimally invasive closure of transthoracic VSD in the medical centre were considered.
From September 28, 2017, the minimally invasive closure of transthoracic VSD was started in our centre. Te TTMPB will start to be performed in the surgery if there was no contradiction at our medical centre on December 23, 2020. Terefore, we divided the patients into two groups: those who underwent TTMPB were assigned to the TTMPB group, while the others were assigned to the non-TTMPB group.

Patients.
From September 28, 2017 (when the surgery started in our centre) to July 25, 2022, a total of 119 paediatric patients scheduled for minimally invasive transthoracic VSD closure were considered for inclusion. Te exclusion criteria were as follows: (1) transfer to open surgery; (2) transfer to the paediatric intensive care unit (PICU) with intubation after surgery; (3) transfer to interventional closure of VSD by percutaneous puncture; and (4) severe pulmonary hypertension.
Demographic data, such as sex, age, weight, duration of anaesthesia, duration of surgery, and time to extubation, were retrieved from medical records. Complications related to TTMPB were also retrieved from the records.
Fifteen minutes before the end of the surgery, the patients were intravenously infused with fentanyl (0.5-1 μg/kg) as an analgesic. Te patients were then transferred to the postanesthesia care unit (PACU) at the end of surgery. Te modifed Aldrete scoring system was used as discharge criteria [11]. Te patients were assessed every 15 min and transferred to the PICU for further observation if the scores were >12.

Te TTMPB Procedure.
A linear probe (L11-3, iE33, Philips, Te Netherlands) was used to guide the procedure after anaesthesia induction and intubation. Te probe was inserted into a sterile sheath and positioned one centimetre lateral to the sternum in a parasagittal manner for the purpose of counting ribs. At the intercostal space between the fourth and ffth ribs beside the edge of the sternum, a 20G 50 mm block needle was placed using the in-plane technique. When the tip of the needle reached the interfacial plane between the transverse thoracic and inner intercostal muscles (Figure 1(a)), 1 ml of saline water was injected to confrm the location through hydrodissection. Subsequently, 1.5 mg/kg (0.30%) ropivacaine was recommended to be injected on each side (no more than 150 mg) in our medical centre (Figure 1(b)). Te TTMPB procedure was performed before the start of the surgery.

Te Puncture of Surgery.
After all the anaesthesia-related procedures were completed, the child was in the supine position. Te position, size, and edges of the VSD and aortic valve were evaluated by transoesophageal echocardiography. A 2-4 cm incision was located in front of the lower end of the sternum for perimembranous VSD or in front of the middle sternum for subarterial VSD. In perimembranous VSD, the mediastinum was entered through the lower part of the sternum. In subarterial VSD, the skin incision was pulled to the left, and the mediastinum was entered through the third intercostal space on the left edge of the sternum.

Outcomes and Defnition.
Te perioperative opioid consumption and the postoperative 24 h rescue analgesia were calculated. Te time to extubation, PACU stay, and postoperative PICU stay were also retrieved from medical records.
Te perioperative opioids were all the opioids consumed from the anaesthesia induction to the end of surgery. Te postoperative rescue analgesia was calculated from the end of surgery.

Statistical
Analysis. Qualitative data are presented as percentage/composition ratios. Quantitative data are presented as the mean ± standard deviation. Te Kolmogorov−Smirnov test was used to test the normality of the quantitative data. Te Levene's test was used to test the equality of variance. Depending on the distribution and equality, an independent t-test or Mann−Whitney test was used to compare diferences. Multiple linear regression was used to do the multivariate analysis. A general linear model (GLM) was also used to assess diferences in heart rate and blood pressure between the TTMPB and non-TTMPB groups at each time point. Te response variable was the diference in the heart rate and blood pressure variation with two factors: group (the intervention) and time (before and after TTMPB). Te interaction (group × time) was evaluated to determine if the efects were diferent between TTMPB and non-TTMPB over time. Two-tailedp values of <0.05 were considered signifcant. Statistical analyses were performed with SPSS software (version 22.0; IBM Corporation, Armonk, NY).  Furthermore, the postoperative PICU stay in the TTMPB group was signifcantly shorter than in the non-TTMPB group (1.04 ± 0.28 days vs. 1.34 ± 1.05 days, p � 0.005, Table 1).

Results of Multivariate Analysis.
Te signifcant diferences in age between the two groups might afect the results, including the time to extubation, PACU, and the postoperative PICU stay. Terefore, we did multivariate analysis through multiple linear regression. Te results demonstrated that TTMPB was signifcantly associated with less time to extubation (B � −22.40, p < 0.001), PACU (B � −15.07, p � 0.001), but not postoperative PICU stay (B � −0.27, p � 0.094).

Results of Repeated Measurements
. Te blood pressure changed over time (p = 0.034 for systolic pressure, p = 0.018 for diastolic pressure; Figure 2), there were no signifcant diferences between the TTMPB and non-TTMPB groups through GLM analysis (p = 0.063 for systolic pressure, p = 0.065 for diastolic pressure; Figure 2). However, the heart rate changed over time with the diference between the TTMPB and non-TTMPB (all p < 0.001, Figure 3).

Discussion
Tis study showed that TTMPB could signifcantly shorten the time to extubation and PACU stay in paediatric patients who underwent minimally invasive closure of the transthoracic VSD. Te heart rate was more stable in the TTMPB group than in the non-TTMPB group.
TTMPB could provide satisfactory pain control because the asteria chest wall was blocked for sensory block distribution between T2-T6 [12]. A canine cadaver study also suggested that a single injection of TTMPB under ultrasound guidance could provide staining of three to four intercostal nerves [13]. Terefore, TTMPB has been found to be efective in several types of pain management, including post-thoracotomy pain syndrome and breast surgery [14,15]. Furthermore, because TTMPB is superfcial and ultrasound-guided, it is safe and easy to perform [16]. A previous study demonstrated that only a few self-limiting complications occurred in ultrasound-guided TTMPB, though future studies are required to confrm the results [17]. Compared to paravertebral and epidural analgesia, which are used for anterior chest wall analgesia and require lateral positioning, TTMPB is performed in the supine position. Te unchanged position after anaesthesia induction might shorten the total anaesthesia time and provide hemodynamic stability. Te present results demonstrated that heart rate was more stable in the TTMPB group than in the non-TTMPB group. Based on the block range of the anterior chest wall, the application and efects of TTMPB in open cardiac surgery with a median sternotomy were explored [18]. In comparison with open cardiac surgery, the present study demonstrated that TTMPB also showed benefcial efects in the minimally invasive closure of transthoracic VSD.
VSD is one of the most common congenital heart diseases in paediatric patients. With the advancement of transcatheter techniques and surgical development, minimally invasive closure of transthoracic VSD has been widely used in China [1,19]. Although this minimally invasive procedure leaves a smaller puncture on the chest surface than the conventional median sternotomy incision, postoperative recovery remains challenging. As a newly developed regional anaesthesia technique, TTMPB was found to provide good perioperative analgesia to promote postoperative recovery in both adult and paediatric open cardiac surgery [9,20,21]. It has been shown that in children undergoing cardiac surgery through a median sternotomy, TTMPB can signifcantly decrease perioperative fentanyl consumption and reduce postoperative pain intensity [22]. Considering paediatric patients who undergo minimally invasive transthoracic VSD closure, the present study also suggested that TTMPB could signifcantly shorten the time to extubation and the PACU stay. However, TTMPB did not reduce the postoperative 24 h rescue analgesia requirement. It might be attributed to the limited duration of action of local anaesthetics.
As an important component of multimodal anaesthesia in cardiac surgery, regional anaesthesia has been used widely in cardiac surgery [23]. However, regional anaesthesia techniques showed limited impact on major clinical outcomes, though they can efectively treat pain [24,25]. With the development of minimally invasive cardiac surgery, the incisions also move toward being smaller. Te multimodal anaesthetic techniques which help with pain control and postoperative recovery in minimally invasive cardiac surgery [26]. To the best of our knowledge, this study flls the gap in exploring TTMPB in paediatric patients who undergo minimally invasive closure of transthoracic VSD.
However, there are several limitations to this study. First, it was a retrospective study that included a limited size of paediatric patients. Te sample number in previous studies that explored TTMPB performed in open cardiac surgery was no more than 100 [18,22]. Demographic characteristics were not comparable between the TTMPB and non-TTMPB groups. Tough multivariate analysis was used, the results need to be confrmed in future randomized controlled trials. Second, TTMPB was performed under general anaesthesia, and dermatomal block could not be assessed. Although all TTMPB were performed under ultrasonic guidance by the same anesthesiologist, the actual block range of the intercostal nerves was unknown in the present study. Tird, patient-controlled analgesia was not used for minimally invasive closure of the transthoracic VSD in our medical centre. Fourth, this study only analysed the postoperative 24 h period of rescue analgesia but not pain scores due to its retrospective nature and the fact that the included patients were paediatric. Moreover, the pain scores in postoperative periods, including PACU and PICU stays, were also lacking. Terefore, the efects of TTMPB on pain cannot be generalisable beyond 24 h.
In conclusion, this retrospective study showed that TTMPB was a benefcial and safe regional anaesthesia technique for paediatric patients who underwent minimally invasive transcatheter device closure of the VSD, although prospective randomized controlled trials are needed to confrm the results.

Data Availability
Te datasets used and analysed during the current study are available from the corresponding author on reasonable request.  Blood Pressure (mmHg) Figure 2: Blood pressure at diferent time points. T1, 10 min before TTMPB; T2, skin incision; T3, 1 h after surgery; T4, end of surgery. For systolic pressure: p � 0.034 over time change, p � 0.063 between the two groups, p � 0.549 for interaction; for diastolic pressure: p � 0.018 over time change, p � 0.065 between the two groups, p � 0.915 for interaction; TTMPB: transversus thoracis muscle plane block.