Erector spinae plane block versus wound infiltration for pain management in minimally invasive transforaminal lumbar interbody fusion: A randomized controlled trial

Introduction: Lumbar spine fusion surgery is one of the most commonly performed elective surgery in orthopaedic practice. This procedure is associated with significant pain because of muscle dissection, implantation, and longer surgical duration. Out of 179 different surgical procedures, spinal fusion surgery patients experienced the most severe postoperative pain on the first day of surgery(1). Postoperative pain is associated with increased analgesic requirement, delayed mobilisation, increased hospital stay and thereby increasing cross-infections(2). Effective pain control in the postoperative period is associated with early mobilisation, decreased deep vein thrombosis, and respiratory tract infections.

Currently, postoperative pain can be tackled in multiple ways, Intrathecal administration of opioids like morphine is technically challenging it is associated with adverse effects like dependency, pruritus, bradycardia, hypotension, respiratory depression, or arrest (dose-dependent)(3). The use of intravenous agents like NSAID (Non-steroid anti-inflammatory drug) is associated with systemic side effects and their analgesic effect remains inconclusive(4).

A new innovative approach to control pain is erector spinae plane block before surgery with the help of ultrasound by avoiding neurovascular structures in the vicinity. It has its own advantages like pain is tackled close to damaged tissue. Another procedure is to give wound infiltration at the end of surgery. Our primary goal in doing this study is to evaluate the analgesic needs between these two procedures and a control group.

Review of literature:

In 1993, H kehlet et al. introduced the idea of enhanced recovery after surgery (ERAS)(5), which aims to improve the patient’s recovery after surgery by minimizing discomfort during the postoperative phase. Pre-emptive analgesia, initially proposed by Crile in the early 1900s(6), is the practice of reducing postoperative pain by giving analgesics before surgical incisions. Later, Woolf, Wall(7), and others expanded on Crile’s hypothesis and proposed that analgesia might be attained by preventing cerebral and peripheral sensitization. Both peripheral and central nerves may become sensitized as a result of local tissue injury. By preventing sensitisation at the damaged muscle level will help to achieve early recovery.

The administration of a "high volume of diluted, long-acting local anesthetic" in tissue structures to produce analgesia is referred to as "local infiltration analgesia" (LIA). Local anesthetics inhibit nerve terminals’ voltage-gated sodium channels (8). By inhibiting the local inflammatory response to injury and preventing the transmission of pain signals from nociceptive afferents in the wound surface, application of LA (Local anesthetic) directly to wounds reduces the release of inflammatory mediators from neutrophils and reduces the formation of edema(9). Pleotropic effects of local anesthetics include neuroprotective, anti-hyperalgesia, and antioxidant qualities.

A long-acting local anesthetic with a lower risk for neurotoxicity and cardiotoxicity is ropivacaine (amino amide). Using the effects of peripheral vasoconstriction, ropivacaine (0.25–0.75%) reduces local blood flow at the injection site(10). In the first 48 hours following surgery, wound infiltration with ropivacaine may offer more effective analgesia during rest and activity, resulting in decreased mean arterial pressure, heart rate, and sufentanil intake, as well as a quicker recovery from surgery and a diminished stress reaction(11).

Pre-emptive analgesia with Erector spinae block (ESB) involves infiltration of local anesthetic between transverse process & erector spinae muscle fascia to block dorsal rami spinal nerves. ESB was first used by Forero et al., in 2016 for management of chronic thoracic neuropathic pain(12). The most likely main mechanism is a direct action of the local anesthetic on neuronal structures in the fascial plane, deep in the erector spinae muscles and surrounding tissue compartments, through physical distribution and diffusion. ESB blocks dorsal and ventral rami of spinal nerves providing analgesia. In a randomised controlled trial conducted by Bellantonio et al., ESB reduced intraoperative fentanyl consumption, lowered morphine consumption postoperatively, and higher satisfaction rate(13). In a retrospective study by Robert J. Owen et al., ESB reduces postoperative opioid consumption and length of hospital stay following spine fusion(14).

 Material and methods:

Study design: Prospective single-blinded randomized controlled trial

Patient Recruitment:

A total of 96 patients undergoing minimally invasive lumbar spine transforaminal interbody fusion (MITLIF) surgeries in the department of spine surgery, BLK Max Super specialty hospital will be included in the study over 6 months.

Inclusion criteria:

1. Age of patient 18 -80 years.

2. Patient undergoing elective MITLIF surgery not more than two levels.

3. Patients with American Society of Anaesthesiologists (ASA) physical status ≤ 3.

4. Patients who provide informed written consent for participation in the study.

Exclusion criteria:

1.Intradural pathologies.

2. Pathologies involving the cervical spine and thoracic spine.

3. Patients who have undergone a previous lumbar spine surgery.

4. Patient who underwent open lumbar spine fusion surgery.

5. Patients with American Society of Anaesthesiologists (ASA) physical status >3.

Grouping and blinding method:

All patients will be randomly assigned to one of three groups using computer-generated randomization with a 1:1 sequence ratio. The first group (Group E) will receive erector spinae block with ropivacaine before start of surgery. The second group (Group W) will receive wound infiltration at the end of surgery. The third group (Group C) will receive an equal volume of placebo. All groups will receive an i.v., PCA pump (patient-controlled analgesia) with fentanyl for post-operative pain control.

Aims and objectives:

1.To compare the amount of fentanyl requirement in i.v., PCA at the end of 24, and 48 hours among the three groups.

2. To compare the VAS (Visual analog score) scores at 3, 6, 12, 24, and 48 hours between the three groups.

3. To compare quality of sleep using Richards-Campbell sleep questionnaire

4. To Compare intraoperative opioid, muscle relaxant consumption, and operative time in all three groups

5. To assess and compare Oswestry Disability Index in all groups.

Treatment process:

Surgery will be performed under general anaesthesia in prone position. In group E patients will receive erector spinae plane block with a dose of 20ml of 0.4% ropivacaine injected at transverse process of L3 on either side before the start of surgery. Ropivacaine was injected in between transverse process and fascia covering over erector spinae muscle. In Group W patients will receive 20ml of 0.4% ropivacaine on either side of wound just before closure of wound. In group C patients will receive an equal volume of normal saline. All patients in three groups will be given a PCA pump with a loaded full dose of 10ml of 500mcg fentanyl mixed with 40ml of normal saline to make a total volume of 50ml. With each dose button pressed, patient will receive 25mcg/2.5ml of fentanyl. The locking period of PCA pump is 20 minutes.

Ethics Review: The study will be conducted after prior approval of the institutional Ethics committee.

where,

        |z1-α

= 1.645 for 5% level of significance

     |z1-β

= 0.84 for 80% power

      |σ1, σ2

= anticipated SD of the two populations

|δ

= minimum medically important difference between means to be detected

Sample size: The outcome of interest in present study is the difference in post-operative analgesia as measured primarily by the amount of fentanyl requirement (Objective 1). The article by Patel et al.(15) reported total opioid consumption 103.70 *±*13.34 mcg in ESPB group and 142.59 *±*40.91 in the control group. Thus, Ïƒ1 = 13.34 and Ïƒ2 = 40.91. The relevant sample size formula for this setup is as follows:

To be able to detect a difference of at least 20 mcg (δ = 20) with a power of 80% at a significance level of 5% (one-tail because the increase in fentanyl in the ESPB group can be safely ruled out), the minimum sample size comes is 29 per group as per the above-mentioned formula. Thus, taking a sample of 29 in each group with 10% attrition rate makes it 32 in each group. So, a total of 96 people studied in the present study.

 Data collection & statistical analysis plan:  The data will be computed on an excel sheet and SPSS (Chicago, IL, USA) software will be used for statistical analysis. The data will be presented as the mean ± standard deviation (mean ± SD) and frequency (percentage). The chi-square test will be used to analyse categorical variables, and Student’s t-test will be used to analyse continuous variables appropriately. P<0.05 will be considered statistically significant.

Expected Outcome:Erector spinae block is superior to wound infiltration and control group with respect to post operative pain management in minimally invasive transforaminal lumbar interbody fusion.