Ultrasound-Guided Erector Spinae Plane Block for Lumbar Spinal Stenosis Surgery

Background: In this retrospective observational study, we evaluated patients who underwent elective lumbar stenosis surgery between February 1, 2019, and April 1, 2019. Patients who underwent surgery for lumbar spinal stenosis under general anesthesia alone were compared with those who underwent general anesthesia combined with erector spinae plane block. Aims: We aimed to retrospectively evaluate whether erector spinae plane block reduced opioid consumption following surgery for spinal stenosis. Study Design: A retrospective observational study. Methods: We collected data on the pain scores, time for the first requirement for patient-controlled analgesia with tramadol, the cumulative patient-controlled analgesia dose, requirement for rescue analgesia, time to first stand up postoperatively and the incidence of postoperative nausea and vomiting. Results: Sixty patients were included in the study. The numerical rating scale’s pain scores were significantly lower in the erector spinae plane group at 1, 2, 4, 6, 12 and 24 hours than in the general anesthesia group. The cumulative dose of patient-controlled analgesia with tramadol was higher in the general anesthesia group than in the ESP group [212.0 (6.6) mg, vs. 107.3 (36.9 mg), (p <0.001)]. The time to first stand up after surgery was significantly longer in the general anesthesia group (p = 0.011). Conclusion: ESP block appear to be an effective method to relieve pain after lumbar surgery.


Introduction
Lumbar spinal stenosis surgery may be performed using different techniques and incurs a cost of approximately 1.65 billion dollars per year in the USA. It is a complicated surgical procedure that leads to significant postoperative pain and adequate analgesia requirement [1]. Lumbar spine surgery may lead to prolonged hospital stay with progression from acute to chronic pain [2]. Adequate postoperative pain relief is essential as patients may already be suffering from chronic pain [3]. Intravenous opioids may be used for postoperative pain relief; however, the relatively high dose required may lead to complications, including nausea, vomiting, respiratory depression, and delirium [4]. Surgeons do not prefer epidural anesthesia as it involves injection at the operative site [5].
The exact mechanism of action of the ESP block remains unclear. Spread of local anesthetics thorough ventral and dorsal rami of spinal nerves [6] [19] [20] or into the paravertebral space has been suggested. Recent cadaveric and magnetic resonance imaging studies also reported conflicting results [20] [21] [22]. Therefore, we aimed to retrospectively evaluate whether erector spinae plane block reduced opioid consumption following surgery for spinal stenosis.

Materials & Methods
Approval was obtained from Namık Kemal University ethics committee with the protocol number 2019.197.10.18, dated October 30, 2019. The study was conducted under the Consolidated Trial (CONSORT) statement and the Helsinki Declaration ( Figure 1).

Study Design
This retrospective observational study of a historical cohort was conducted in a university hospital. The ethics committee of the university approved the study design as a retrospective review of patient records. The medical records of patients who underwent lumbar spinal stenosis surgery between February 1, 2019, and April 1, 2019, were reviewed by a resident who was not involved with the study. Patients with American Society of Anesthesiologist (ASA) physical status I-II, aged 18-65, underwent elective lumbar spinal stenosis surgery and received patient-controlled analgesia (PCA) postoperative pain relief were included in the study. Patients with missing data were excluded from the study.
Lumbar spinal stenosis surgery is performed in our clinic by a single surgical team, and General Anesthesia (GA) is routinely carried out. Information about ESP block is provided to all patients with no contraindications for the procedure during the preoperative visit. The block is performed under GA just before the commencement of surgery after obtaining written informed consent. PCA with tramadol is prepared as part of the postoperative analgesia protocol regardless of the block's performance. Postoperative pain management is routinely followed up and documented in patients who receive PCA.
We collected demographic and surgical information, such as age, gender, height, weight, body mass index, surgery duration, and anesthesia. Clinical information such as the Visual Analog Score (VAS) in the Post-Anesthesia Care Unit (PACU), time to the first requirement for PCA, the total tramadol dose administered by PCA, the requirement for rescue analgesia, the time taken to stand up for the first time after the surgery, and the incidence of Postoperative Nausea and Vomiting (PONV) were obtained from patient records.

Patient Groups
We enrolled patients who underwent lumbar spinal stenosis surgery between February 1st, 2019, and April 1st, 2019. After reviewing archived files, patients who underwent GA were included in the "GA group"; patients who had GA combined with ESP block were included in the "ESP Group." All information was collected from patient records from the file archive of our clinic.

Anesthetic Technique
GA was administered to all the patients. The patients were monitored with 3-channel electrocardiography, non-invasive blood pressure, peripheral oxygen saturation, and Bi-Spectral index (BIS) in the operating room. After obtaining intravenous access, an infusion of normal saline was commenced. After 3 minutes of pre-oxygenation with 100% oxygen, anesthesia was induced intravenously with 2 -3 mg/kg of propofol, one mcg/kg of fentanyl, and 0.6 mg/kg of rocuronium. After ensuring adequate muscle relaxation, orotracheal intubation was carried out by an experienced anesthesiologist. Anesthesia was maintained with 1% -2% sevoflurane in 4 L of 40%:60% O 2 and air mixture. An infusion of remifentanil was commenced at 0.1 -2 mcg/kg/min after intubation until skin closure. Intravenous ondansetron, 4 mg was administered for PONV, and 20 mg tenoxicam was administered for preemptive analgesia. The concentrations of sevoflurane and remifentanil were set to a target BIS level between 40 and 60. Intravenous rocuronium was administered in a dose of 0.1 mg/kg to maintain adequate muscle relaxation. After skin closure, all anesthetic agents' administration was ceased, and neuromuscular blockade was reversed with 0.01 mg/kg atropine and 0.04 mg/kg neostigmine intravenously once the patient started breathing spontaneously.
Following successful extubation, patients were transferred to the Post-Anesthesia Care Unit (PACU) for continued monitoring. Supplemental oxygen was administered at 2 L/min through an oxygen mask for 20 -30 minutes. Patients with a nine or more score on the modified Aldrete score were discharged from the unit to the surgical ward after 30 minutes.

Application of Block
Patients were carefully placed in the prone position after induction of anesthesia, before the commencement of surgery. All necessary precautions were taken to avoid complications involving the prone position after anesthesia induction with continued orotracheal intubation. We used an ultrasound machine with a high-frequency (1 -8 MHz) convex probe. After aseptic preparation, the ultrasound probe was first placed in a cephalo-caudal orientation at the mean surgical level's spinous process. It was then moved laterally to one side by 3 cm. The sono-anatomic landmarks, including the erector spinae muscles and the transverse process at the block's predetermined level, were identified. A 100-mm 21-gauge needle was inserted using an in-plane technique in a cephalo-caudal direction under real-time ultrasound guidance. After confirming the position of the tip of the needle over the transverse process by hydrolocalization with 2 -3 ml isotonic saline solution, 20 ml 0.25% bupivacaine was injected. The spread of local anesthetic in a plane below the erector spinae muscle was visualized. The procedure was repeated on the contralateral side. The surgical procedure was commenced after the completion of the block. In patients who did not consent for the block, surgery was carried out under general anesthesia alone. None of our patients experienced any complications related to regional or general anesthesia.

Evaluation of Pain
Evaluation of postoperative pain was commenced in the PACU and continued in the surgical ward using the 11-point Numerical Rating Scale (NRS). The NRS is a segmented, numeric version of the visual analog scale with scores ranging from 0 to 10, with 0 representing "no pain" and ten indicating "the worst pain imaginable". Pain scores were recorded by one of the researchers at 30 min (in the PACU), and 1, 2, 4, 6, 12, and 24 hours postoperatively according to our postoperative pain management protocol.

Routine Analgesia Protocol and Rescue Analgesia
Intravenous PCA was administered to all patients with a solution of 3 mg/ml of tramadol (300 mg tramadol mixed in 100 ml isotonic saline). The bolus dose was set at 20 mg with a lockout period of 20 minutes, with no background infusion. PCA was commenced in the PACU and continued for at least 24 hours in the surgical ward. Rescue analgesia was administered as follows: 1 g paracetamol intravenously if the VAS score was four and above, and 50 mg meperidine intravenously if it persisted after 1 hour.

Outcome Measures
The study outcomes included the total postoperative tramadol consumption in the first 24 hours and the NRS scores in the PACU and at 1, 2, 4, 6, 12, and 24 hours postoperatively. The incidence of postoperative nausea and vomiting and the requirement of rescue analgesia were also evaluated.

Sample Size
The sample size was calculated using G*Power 3.1.9.3 for the Mac program based on previous studies found in the literature. A reduction in tramadol consumption by at least 30% in the 24-hour postoperative period was considered clinically significant. Assuming an alpha error = 0.05 with a power of 80%, we calculated a minimum sample size of 28 patients in each group.

Statistical Analysis
Descriptive data are presented as numbers and percentages for categorical variables; continuous variables are expressed as mean (SD) or median (IQR). The normality test was performed for continuous variables using the Kolmogorov Smirnov test. We analyzed data including age, gender, height, weight, BMI, duration of anesthesia and surgery, duration of stay in the PACU, time to the first dose of PCA, the total PCA dose, and the time taken to stand up for the first time after surgery. The Pearson Chi-square test was used to analyze categorical variables per data type and distribution. The independent samples t-test was used for normally distributed variables; the Mann Whitney U test was used for variables that were not normally distributed. All analyses were performed using R-3.6.0 (for Windows. The R-project for statistical computing) and Jamovi project (2018) Jamovi (Version 0.9.6.9) [Computer Software] (Retrieved from https://www.jamovi.org). A p-value of less than 0.05 was considered statistically significant.

Results
Patients who underwent elective lumbar stenosis surgery between February 1st, 2019, and April 1st, 2019 were enrolled in the study. We obtained records of 62 patients who met the inclusion criteria from the file archive. Two patients with missing data were excluded.
Comparing the demographic and clinical characteristics of patients in the ESP and the GA groups is presented in Table 1 and Table 2. Age, gender, weight, and BMI levels were similar between both groups (p > 0.05 for each, Table 1). Patients in the GA group were significantly taller than those in the ESP group (p = 0.029).  The duration of anesthesia (p = 0.036) and surgery and (p = 0.020) was significantly longer in patients in the GA compared to the ESP group. The Median VAS score in the PACU was higher in the GA group (p <0.001), and the median time for the first dose of PCA was less in the GA group (p <0.001). The mean cumulative PCA dose of tramadol was 212.0 (6.6) mg in the GA group compared to 107.3 (36.9) mg in the ESP group (p <0.001). The time to first stand up after surgery was significantly longer in the GA group (p = 0.011).
The VAS scores among patients in the ESP group were lower at 1, 2, 4, 6, and 12 hours compared to the GA group (Table 4). VAS scores according to groups are presented in Figure 2.

Discussion
This study evaluates the use of ultrasound-guided erector spinae plane block in providing postoperative analgesia after spine surgery. We found that the use of ultrasound-guided erector spinae plane block results in a significant reduction in postoperative opioid consumption and contributes significantly to pain relief. Spinal surgery is associated with significant postoperative pain. Optimization of postoperative pain management is an essential consideration for the anesthesiologist [23]. Appropriate postoperative pain management is also associated with fewer postoperative complications and reduced hospital stay length [24].
Reducing opioid-based analgesia requirement is recommended to provide adequate postoperative analgesia with fewer side effects, including postoperative nausea and vomiting, respiratory depression, and hypotension [25] [26].
ESP block is currently popular and is used in routine anesthetic practice for spine surgery, cholecystectomy, gastric hernia repair, mastectomy, thoracotomy, analgesia for rib fractures, and treatment herpes zoster pain [15]  We aimed to retrospectively evaluate whether ESP block reduced opioid consumption following surgery for spinal stenosis. We preferred to perform the block after induction of GA under ultrasound guidance before the commence-

Conclusion
The ESP block provides a practical postoperative analgesic effect for 24 hours in patients undergoing lumbar spinal stenosis surgery and reduced opioid consumption.