General anesthesia along with epidural analgesia is commonly performed technique for surgeries associated with severe post-operative pain. Surgical procedures result in release of inflammatory mediators leading to delay in wound healing associated with longer hospital stay and financial burnout of caregivers. The usual analgesic regimen for postoperative pain is through intravenous route, sometimes limiting the doses of the drugs due to cumbersome side effects. Ultrasound guided regional blocks leads to more accurate placement of the local anesthetics and decreasing the incidence of complications associated with performing the block.

Erector spinae plane block (ESPB), an interfascial plane block which blocks both somatic and visceral nerves to provide analgesia. It was first introduced by Forero et al. in 2016 as a mode of analgesia in patients with thoracic neuropathic pain [1]. The site of action is the thoracic spinal nerves through the blockade of the ventral and the dorsal rami. This block is indicated for thoracic surgeries to upper abdominal surgeries.

In this study, we hypothesize that the ESP block with morphine as additive may provide superior analgesic efficacy due to its long duration of action as compared to dexmedetomidine.

Dexmedetomidine is a potent α2 agonist, emerging as an adjuvant to regional anesthesia and analgesia by prolonging and enhancing the analgesic effect of the regional blocks [10-12]. Morphine is the prototype opioid agonist, the analgesic action of morphine administered through epidural route results from binding to receptors µ, delta and kappa type of opioid receptors.

Study Design and Participants

The study was a randomized, double-blinded, comparative study where the patients and observers were blinded about the group. After obtaining the Institute Ethics Committee’s (IEC 2021/EC/2691) approval, written informed consent was taken from the patients of American Society of Anesthesiologists (ASA) physical status I and II, aged 18-65 years, who were scheduled for elective lumbar spine surgery under general anesthesia. Ninety patients were included in our study between January 2021 and July 2022. Those who refused to participate or those with known allergies to the study drugs, infection at the site of block, coagulopathy, significant cardiac, renal, neural and liver disease, obesity was excluded. The patients were randomized into two groups (45 each); group M and group D, using sealed opaque envelopes concealing the randomization number. To achieve blinding the drugs were loaded in similar syringes with equal total volumes by staff nurse who was not involved in the study.

All patients included in the study were thoroughly assessed preoperatively by history, physical examination, and laboratory investigations. At the preoperative visit, all patients were instructed on how to evaluate their own pain by using the 11-point Numeric Rating Scale (NRS) pain score, which ranges from ‘0’ (meaning no pain) to ‘10’ (meaning worst pain). On the day of surgery, patients were premedicated in the preoperative area with intravenous ranitidine 50 mg and metoclopramide 10 mg one hour prior to scheduled time of surgery. On coming to the operation theater standard ASA monitors were attached. Anesthesia was induced with midazolam 30 mcg/kg, fentanyl 2 mcg/kg and propofol 2 mg/kg, after checking adequate bag-mask ventilation muscle relaxant vecuronium 0.1 mg/kg was given. Trachea was intubated with adequate size armored endotracheal tube and secured after confirmation of position. Anesthesia was maintained using oxygen, air, and isoflurane at fresh gas flow of 3 l/min to maintain a MAC of 0.8-1.0% and volume-controlled ventilation. Patients were made prone and all pressure points were adequately padded. Muscle relaxant was repeated as per requirement.

Block Procedure

Both groups received the ESP block under all aseptic precautions placing patients in the prone position after general anesthesia. A high-frequency linear probe (13-6 MHz) was placed longitudinally in the paravertebral region at the lumbar level (L2) vertebra. A 22-G, Quincke spinal needle was introduced using the in-plane technique in a craniocaudal direction to make a contact with the transverse process. After hydro-dissecting the plane, group M received 0.25% bupivacaine 18 ml along with morphine 50 mcg/kg (total volume 20 ml) was injected below the ESM, just above the transverse process. Similarly, group D received 0.25% bupivacaine 18 ml along with dexmedetomidine 1 mcg/kg (total volume 20 ml) was injected below the ESM, just above the transverse process [Figure 1].

The local anesthetic was injected in 5 ml increments, with aspiration after every 5 ml to prevent inadvertent intravascular injection. Electrocardiogram, non-invasive blood pressure, end-tidal carbon dioxide and oxygen saturation were monitored intraoperatively and recorded at o min, 1 min, 3 min, 5 min, 10 min, 15 min, 20 min, 30 min, 1 h, 2 h, 3 h, 4 h, 6 h, 8 h, 12 h and 24 h. All the patients were extubated at the end of surgery; 0.1 mg/kg intravenous ondansetron was administered as anti-emetic prophylaxis, and 15 mg/kg intravenous paracetamol was administered intraoperatively to all patients. Patients were shifted to post-anesthesia care unit (PACU) and post-operative analgesia was assessed by Numeric Rating Scale (NRS) pain score and hemodynamic parameters were recorded at 1, 2, 4, 6, 8, 12, 18, and 24 hours, post-operatively. The time to first rescue analgesia (tramadol 1 mg/kg slow intravenous injection), the number of doses of rescue analgesic were recorded. Complications such as nausea, vomiting, urinary retention, motor weakness and respiratory problems were managed accordingly.

Statistical Analysis

The sample size was calculated using data from Kamel et al. [5] which used similar   interventions as   in    the    present study. The sample size was chosen so as to maintain the overall alpha error <0.05 and power (1-β) > 0.9 and to provide additional safety and tolerability data. We enrolled 45 patients in each group. The statistical analysis of data was performed using SPSS, version 23 IBM Corp. Data are presented as median (range), mean (SD), or frequencies as appropriate. Chi-square test was used for categorical variables and Student’s t-test for quantitative variables.

Figure 1: Ultrasound image of various structures seen while performing   Erector   spinae    plane   block

As per the CONSORT flow diagram, 101 patients were screened, 90 were eligible and were randomized (Figure 2). All randomized participants (n=90) received the allocated treatment (Group M: n=45, Group D: n=45). There were no statistically significant differences in demographic, anesthetic, and surgical characteristics of the two intervention groups (Table 1). The intraoperative variables of the time taken for surgery; hemodynamic parameters were compared between the two groups. The NRS score differed significantly between the two groups after 1 hour in postoperative period (p <0.05) (Table 2). The time for the first requirement for rescue analgesia was found to be significantly longer in group M (13.76 ± 2.577 hours) than in group D (7.20 ± 1.687 hours) (P < 0.05), as shown in Table 2. There was no significant difference between the groups in terms of hypotension (p = 0.078) and pruritus (p = 0.40) (Table 3). The patients in group M have more episodes of nausea and vomiting than the patients in group D which was significant (p < 0.05).

Figure 2: CONSORT flow diagram

Table 1: Demographic data and operative characteristics

Data are presented as the mean ± standard deviation (SD) or as the number of patients. p-value <0.05: significant.

Table 2: NRS score between two groups postoperatively, rescue analgesia time (hours)

Data are presented as the mean ± standard deviation (SD) or as the number of patients. p-value <0.05: significant.

Table 3: Postoperative complications

Data are presented as the number of patients. p-value <0.05: significant.

ESP block is given for postoperative analgesia in surgeries involving the posterior thorax, chest and abdomen. The mechanism of ESP block involves the spread of local anesthetic in a cephalad-to-caudal direction in the erector spinae plane [1-4]. It also enter the paravertebral space through the connective tissue complex attached to the transverse process, and then on through the intervertebral foramen, ultimately blocking the ventral and dorsal branches of the spinal nerve. According to the NRS scores after surgery, a significant difference was found between the group M and group D, the duration of analgesia was significantly prolonged in the group M compared to group D. In addition, the group M took a longer time to raise their first request for risqué analgesics compared to group D. Also, the post operative analgesic consumption was significantly lower in group M as compared to group D. However, there was significant difference in terms of postoperative nausea and vomiting being higher in group M that require treatment with ondansetron.

The mechanisms for analgesia with erector spinae block were assumed to have multidermatomal sensory blocks of the posterior, lateral, and anterior thoracic wall [1]. In general, the local anesthetic is injected between the transverse process of the vertebra and the erector spinae muscle fascia. After the injection the local anesthetic spreads caudally and cranially, thus covering a wide dermatomal area. The intention of ESPB is met when both the ventral and dorsal rami of the spinal nerves are impacted [6]. When ESPB is performed at L2, it has potential to cover sensory loss from T10 to L5 [7]. ESPB offers an advantage when compared to other interfascial plane blocks of the thorax and abdomen, such as transversus abdominis plane block, quadratus lumborum, pectoralis nerve block as it also provides visceral analgesia [4].

According to Jin Rao et al. [8] both   nalbuphine   and dexmedetomidine as adjuvant to ropivacaine were comparable in terms of the associated analgesia, sensory block duration, need for rescue analgesia and incidence of chronic pain in patients after video-assisted thoracoscopic lobectomy surgeries (VATLS). In another study, conducted by Jemal et al. [9] in which spinal morphine was compared to transversus abdominis plane (TAP) block for post-operative pain management in patients undergoing caesarean section under spinal anesthesia found that spinal morphine prolonged postoperative analgesia time, superior postoperative analgesia, and less postoperative opioid consumption compared to the TAP block.

Ultrasound-guided erector spinae block with general anesthesia is a safe and effective alternative mode of analgesia in patients undergoing lumbar spine surgery. Morphine as an adjuvant to bupivacaine provides prolonged duration of analgesia as compared to dexmedetomidine.

Limitations

In spite of calculating the sample size, the number of patients included in the study was too small to generalize the study outcomes. Sensorial evaluation of patients was not performed because blocks had been done under general anesthesia. The presence of local anesthetic drug at the site of surgery (when drug spread is in the same plane as surgical site) leads to difficulty in use of electrocautery. This is primarily due to the presence of fluid at the site of electrocautery which increases tissue conductance and thus decreases the function of electrocautery. The patients were followed only for a shorter period of time, i.e. only 24 hours.

Ultrasound-guided erector spinae block with general anesthesia is a safe and effective alternative mode of analgesia in patients undergoing lumbar spine surgery. Morphine as an adjuvant to bupivacaine provides prolonged duration of analgesia as compared to dexmedetomidine.

Limitations

In spite of calculating the sample size, the number of patients included in the study was too small to generalize the study outcomes. Sensorial evaluation of patients was not performed because blocks had been done under general anesthesia. The presence of local anesthetic drug at the site of surgery (when drug spread is in the same plane as surgical site) leads to difficulty in use of electrocautery. This is primarily due to the presence of fluid at the site of electrocautery which increases tissue conductance and thus decreases the function of electrocautery. The patients were followed only for a shorter period of time, i.e. only 24 hours.

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