Ultrasound-guided thoracic paravertebral block for percutaneous kyphoplasty: A prospective non-randomized comparative study

Introduction Kyphoplasty for osteoporotic vertebral compression fractures was short but painful. The purpose of the current study was to investigate the effects and safety of ultrasound-guided thoracic paravertebral block in patients undergoing percutaneous kyphoplasty (PKP). Methods A prospective study of 195 patients with thoracic compression fracture undergoing PKP was conducted. The patients were non-randomly assigned to receive an ultrasound-guided thoracic paravertebral block (Group P, n=96) and local in�ltration anesthesia (Group L, n=99), and were compared along with intraoperative parameters and anesthetic effects. Visual analog scale (VAS) of pain, systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were measured at pre-anesthesia (T0), post-anesthesia (T1), trocar insertion (T2), balloon dilatation (T3), cement injection (T4) and post-operation (T5). Results The anesthesia time was signi�cantly longer in group P than in group L. There were no signi�cant differences in the epidemiological data, operation time, blood loss, hospitalization time complications and costs between the two groups. The additional analgesics rate was signi�cantly lower in group P than in group L. The investigators’ satisfaction scores, patients’ anesthesia satisfaction scores and intention rate of re-administration anesthesia were signi�cantly higher in group P than in group L. Intraoperative VAS score (T1-T4) was signi�cantly lower in group P than in group L. There was no signi�cant difference in VAS scores (T0 and T5), SBP, DBP and HR between these two groups. Conclusion Ultrasound - guided thoracic paravertebral block achieved more effective analgesia in comparison to local in�ltration groups in patients undergoing percutaneous kyphoplasty.


Introduction
With the aging of the population, annual incidence of osteoporosis and its associated fractures is prevalent.Osteoporotic vertebral compression fracture (OVCF) can affect a patient's quality of life, which have become an important health issue [1].Many patients with OVCF have recently undergone percutaneous kyphoplasty (PKP) with good clinical and radiological results [2].
The procedure of PKP is short but painful especially during trocar insertion, balloon dilatation and cement injection.Different anesthetic techniques have been proposed to control pain during kyphoplasty, but all have limitations.General anesthesia adds its own risks for elderly patients and prevents clinical assessment of bone cement leakage during the procedure [3].Although monitored sedative analgesia is a safe and feasible method for PKP, which can be hazardous, especially with the patient in the prone position, as conventional systemic opioid administration entails the potential risk of respiratory depression [4].Local anaesthesia for PKP is effective, well tolerated and easy to use.However, some patients with local anesthesia have severe pain and restlessness during surgery and cannot cooperate with the doctor to complete the operation [5].Thoracic epidural block has a high failure rate and the risk of severe complications such as epidural abscess and spinal hematoma [6].
Thoracic paravertebral block (TPVB) has been studied as a possible alternative to provide high quality analgesia and great advantages for many types of surgery [7-10].Meanwhile, perioperative pain of PKP is also dominated by these nerves passing through the thoracic paravertebral space.Thus, TPVB may be effective for PKP.However, no study has evaluated the TPVB for PKP in patients with OVCF.Therefore, the aim of our present study was to investigate the clinical effect and safety of the ultrasound-guided thoracic paravertebral block (USG-TPVB) for PKP in patients undergoing OVCF.

Study design
Ethical approval for this prospective, non-randomized study was provided by the Ethics Committee of the authors' institute.Patients were given su cient explanation of the study goals and signed a consent form.Inclusion criteria were as follows: 1) elderly (>60 years), 2) MR con rmed fresh single-segment compression fracture between T8 to T12, 3) minor injury or no history of trauma without neurological de cit, 4) the constant ache and fatigue in thoracic vertebrae that can signi cantly affect daily life, 5) being diagnosed with osteoporosis according to T value of bone density test less than -2.5 using dualenergy x-ray absorptiometry(DXA).The excluding criteria were as follows: 1) symptoms of neurological de cits, 2) clinical or imaging evidence of metastatic bone tumor or multiple myeloma, 3) asymptomatic fractures, 4) systemic or local infections and severe bleeding disorders.
From January 2015 to August 2017, 290 consecutive patients received PKP for thoracic OVCF.Following a comprehensive explanation of this study and expected bene ts and risks, fty four patients refused to consent to the study.After applying exclusion criteria, we analyzed 195 patients received USG-TPVB (group P, n = 96) and local in ltration anesthesia (group L, n = 99).The differences between local in ltration anesthesia and USG-TPVB were explained to all patients before surgery, and the anesthetic methods were selected according to patient preference.The clinical characteristics of the 195 patients were summarized in Table 1.
Preoperatively, standard clinical examination and evaluation including the medical history, physical examination of percussion pain, and assessment of pain intensity [visual pain analogue scale (VAS)] were performed.Additionally, X-rays of the relevant spinal region in two planes, computed tomography (CT) scan and magnetic resonance imaging (MRI) (T1w and T2w sequences including fat suppression sequences) and bone density measurement (DXA) were carried out.

Anesthesia procedures
Standard electrocardiogram, non-invasive blood pressure and pulse oximetric oxygen saturation (SpO 2 ) monitorization processes were performed for all patients.Each patient had brief preoperative teaching to rate their pain on the VAS scale (VAS of 0 as no pain and 10 as maximal pain).Furthermore the patients were also noti ed that they could receive additional analgesia in a severe pain event.TPVB and local anesthesia were performed by two experienced attending anesthesiologists.
In group P, after placing the patient in the prone position, the attending anesthesiologist discerned the puncture site using a linear 2-to 5-MHz ultrasound scanning probe (SonoSite S-Nerve, Bothell, Wash), which were placed parallel to the rib.The transverse process, transverse ligament of rib and pleura was carefully distinguished on the ultrasound image (Fig. 1).Needle insertion point was con rmed at approximately 40 mm from the midline by ultrasound.After local anesthesia with 1% lidocaine 5 ml, an 8cm, 18-gauge needle (Peridural Catheter set; B. Braun, Melsungen, Germany) was inserted from lateral to medial under real-time ultrasound monitoring using an in-plane technique.Keep the needle body in the ultrasonic eld of view and guide the needle tip along the intercostal approach into the thoracic paravertebral space.After a negative aspiration test for blood, cerebrospinal uid, or air, 10 ml of 0.5% ropivacaine was injected into the thoracic paravertebral space slowly.The pleura was seen being pressed ventrally during local anesthetic injection.We performed single blocks with 10 ml of 0.5% ropivacaine at the fracture vertebra.An independent observer tested the block by loss of pain sensation in the sensory distribution of the ipsilateral and contralateral vertebral dermatomes 10 mins after block performance.An additional local in ltration anesthesia in the form of 10 mL of 0.5% ropivacaine hydrochloride was required preoperatively when failed USG-TPVB.
Group L was treated with local in ltration anesthesia.The patient was in a prone position.The puncture target point was located by the C-arm X-ray.5 mL of 1% lidocaine hydrochloride was used to in ltrate the skin, subcutaneous tissue, and part of the thoracic muscles.10 mL of 0.5% ropivacaine hydrochloride was injected around the pedicular insertion point.
VAS score more than four indicated an inadequate block.An additional analgesia in the form of dexmedetomidine intravenous injection 0.05mg was required until the VAS for pain score was four or less.

Surgical procedures
All operations were carried out by the same surgical team using the same technique.The manual lordotic manoeuvre was rst performed to correct kyphosis.A 1cm skin incision was made laterally to the desired entry point of the pedicle percutaneously.A trocar (Shandong Guanlong Medicial utensils Co., Ltd., Jinan City, Shandong Province, China) in a cannula was inserted into pedicle at the fractured vertebra through a unipedicular approach as a working channel.After removing the trocar, a balloon was placed into the working channel and slowly in ated to create a low-pressure cavity for cement injection.In ation continued until the balloon pressure up to 300 psi.Then the balloon was de ated and removed, and polymethyl methacrylate (PMMA) cement was injected into the fractured body through the cannula under continuous uoroscopic monitoring (Fig. 2).The cement insertion was considered complete when it reached the posterior third of the vertebral body or had a potential tendency of cortical, epidural, and anterior venous cement leakage.
Student t or Wilcoxon signed rank tests were used to compare measurements between the two groups.Repeated measures variance analysis was used to compare measurements of HR, DP and SBP from T0 to T5. Nominal variables (sex, fracture distribution, additional analgesia rate, and intention rate of readministration anesthesia ) were presented as number (percent) and compared by means of the Chisquare test.A two-sided p value of <0.05 was considered to show a statistically signi cant difference.

Results
No signi cant between-group differences were detected in the patients' sex, age, the distribution of fracture, T-score, height, weight, injury time operation time, blood loss, hospitalization time and cost (Table 1).The anesthesia time was signi cantly longer in group P than in group L (23.73±4.20 min vs. 6.31±2.14min, P<0.05) (Table 1).There was no failed block or need for additional local in ltration anesthesia in this study.
There was no signi cant difference in pain VAS scores (T0 and T5) between two groups (Tables 2).

Discussion
This study showed that ultrasound-guided thoracic paravertebral block provided more effective analgesia in comparison to the local in ltration anesthesia in patients underwent PKP.
Osteoporosis is a progressive, systemic disease and the most common cause of vertebral fractures.OVCF can cause debilitating back pain, functional decline, depression, disability in elderly populations [1].Minimally invasive augmentation techniques such as PKP have become prominent in OVCF treatments [2,   11, 12].However, the issue of pain during this period has not yet been completely solved.
The anesthetic method for PKP usually includes local anesthesia, sedative analgesia, and general anesthesia.Although general anaesthesia for PKP provides has been proven to be effective, elderly patients may increase the risk of anaesthesia-related cardiopulmonary complications.In addition, intraoperative neurological symptoms may not be discovered in a timely manner [3, 13].Sedative analgesia with opioids and benzodiazepines, which controls the patient's anxiety and pain without the need for an intervention to maintain respiratory and cardiac function, may be appropriate for elderly patients with increased general anaesthesia risk.However, the use of sedatives in elderly patients in the prone position may carry the potential for opioid-induced respiratory depression [4, 14].Although subarachnoid and thoracic epidural anesthesia may be effective for PKP, these anesthesia methods are often associated with a high failure rate and complications such as epidural hematoma, infection, hypotension and urinary retention [3, 15].Local anesthesia can keep patients awake during operation.Surgeons discover neurological symptoms in time to avoid nerve damage.Furthermore, the use of local anesthesia avoids the potential complications of sedative and general anesthesia.However, the local anesthetic often results in a painful response, discomfort, anxiety and agitation, and not be well coordinated with the doctor to complete the operation [5, 16, 17].Therefore, it's necessary to nd an alternative anesthesia method for these patients undergoing PKP.However, the method for determining if the patient would receive paravertebral blocks or local anesthesia in ltration preoperative is still controversial.Several studies proposed to predict the amount of postoperative analgesics in patients by measuring the sensitivity of preoperative patients to pain, anxiety, pain threshold, pain tolanrance threshold [18][19][20][21] .Thus, studies on the indication of paravertebral blocks and local in ltration anesthesia for PKP will be included in our future work.
Thoracic paravertebral space is a wedge-shaped region on both sides of the vertebrae.Each thoracic paravertebral space contains adipose tissue, spinal nerves (intercostal nerves), dorsal branches of the spinal nerves, abdominal branches of the spinal nerves, tra c branches, sympathetic trunks, and intercostal vessels [22] .Therefore, injection of a local anesthetic into the gap can block the sensory nerve, motor nerve, and sympathetic nerves passing through the gap, thereby achieving anesthesia effect [23] .The wedge-shaped bottom of the thoracic paravertebral space is lled with loose connective tissue.Local anesthetics can spread superior and inferior along this gap (Fig. 4).So, a single dose of local anesthetic can receive multiple segments of anesthesia [24] [25] .TPVB has been studied as a possible alternative to provide high quality analgesia and great advantages in breast surgery, thoracic and upper abdominal surgery, thoracic myofascial pain syndrome, pain caused by cervical spondylosis, zoster-associated pain, etc [7-10].Meanwhile, perioperative pain of PKP is also dominated by these nerves passing through the thoracic paravertebral space.Therefore, we applied thoracic paravertebral nerve block for PKP.
According to the results of this study, intraoperative pain tolerance and satisfaction of patients with thoracic paravertebral nerve block were signi cantly better than the local anesthesia group.
Although there are no studies in the literature which compared paravertebral block and local in ltration in PKP, there are studies which compared paravertebral block and local in ltration in breast surgery, thorax surgery, mastectomy, percutaneous nephrolithotomy and laparoscopic cholecystectomy [26][27][28][29][30][31] .A study reported the effectiveness of TPVB in reducing postoperative opioid consumption, pain score, and opioidrelated side effects [26,29,31] .However, some studies showed that TPVB did not have any advantages over wound side in ltration [27,28,30] .In our study, dynamic VAS scores and additional analgesia rate in group P were lower than those in group L.
Numerous techniques were applied for TPVB in the literature.Landmark technique (loss of resistance technique) has a high failure rate and complications [32] .Although Nerve stimulator-guided technique can improve the failure rate, the incidence of nerve injury was high when the effectiveness of neurostimulation is affected [33,34] .Several authors also recommend implementations accompanied by ultrasound to reduce the risk of complications [7,8,35,36] .Compared with the X-ray, ultrasound can reduce the radiation damage of both doctors and patients.At the same time, ultrasound can be dynamically multi-planar and multi-angle observation, and the doctor can be instructed to adjust the puncture path in time during the puncture process to reach a satisfactory puncture point.The pleura, lungs, blood vessels and other tissues can be clearly distinguished by ultrasound to choose the appropriate puncture path and avoid the iatrogenic injury during the puncture.
Of course, ultrasound-guided thoracic paravertebral nerve block has puncture failure, pleural, pulmonary, vascular and nerve injury complications [37][38][39][40] .The most important way to improve the safety of the puncture is to use "in-plane technology" to see the entire needle and the needle tip to prevent iatrogenic injury [41] .It is also possible to gently twitch the needle under ultrasound monitoring and observe the movement of the needle to con rm the position of the needle.When the needle reaches the target point, a small amount of local anesthetic can be injected to observe the diffusion of the liquid to con rm the position of the needle tip.When the local anesthetic was injected, the weak echo group can be formed on the outside of the pleura under ultrasound to push down the pleura [41] .Due to limited range of thoracic paraspinal nerve block, sympathetic nerve suppression is mild.Furthermore, the incidence of complications such as oxygen desaturation, respiratory depression, hypotension, hypertension, bradycardia, tachycardia were low.In this study, we applied TPVB with USG by achieving real-time imaging, and we did not encounter any complications such as atelectasis, pneumonia, pneumothorax, hemothorax, epidural injection, spinal anesthesia, Horner syndrome.
In conclusion, ultrasound guided thoracic paravertebral nerve block achieved more effective analgesia by reducing intraoperative pain VAS scores and opioid consumption in comparison to local in ltration analgesia for patients undergoing percutaneous kyphoplasty.Schematic drawings of thoracic paravertebral space.The paravertebral space with approaching needle and surrounding vertebral body, transverse process, and spinous process.The aorta, thoracic duct,

Figure 3 Time
Figure 3