Ultrasound-Assisted Transverse Process Line Guidance Versus Palpation for Neuraxial Blocks: A Randomized Trial on First-Attempt Efficacy

INTRODUCTION

Thoraco-Lumbar neuraxial block is a common technique used for regional anaesthesia and analgesia during abdominal, pelvic, and lower extremity surgeries. Traditionally, this procedure relies on identifying intervertebral spaces through palpation of surface anatomical landmarks. However, in patients with challenging anatomy, obesity, or spinal deformities, achieving successful needle placement can be difficult. Unanticipated difficulties often lead to multiple attempts and failed blocks.

Ultrasound guidance has emerged as a valuable tool to improve the success rate and safety of neuraxial blocks. By visualizing relevant anatomy and needle trajectory, ultrasound can enhance accuracy. However, the optimal ultrasound scanning approach and needle insertion technique are still under debate. The conventional method of scanning the spine and the neuraxial structures involves the placement of an ultrasound probe, scanning from lateral to medial in paramedian sagittal planes to identify the transverse process, the articular processes, the laminae, the spinous process, and the underlying structures. Various probe manipulations are required to correctly identify the interspinous space where the needle has to be placed and advanced to reach the neuraxial structures. This is technically challenging and often time‑consuming for anaesthesia practitioners and trainees who are not well trained in the use of ultrasound. Moreover, real‑time ultrasound needle guidance requires two operators. Therefore, many still rely on the surface landmarks combined with the loss of resistance or the free flow of cerebrospinal fluid techniques for performing central neuraxial blocks.

One of the proposed methods is to use the transverse process line (TPL) as a landmark for identifying the intervertebral space and the midline. The TPL is a horizontal line that connects the tips of the transverse processes of the lower thoracic and lumbar vertebrae on the ultrasound image. The TPL can be easily identified in most patients, regardless of their body habitus. The TPL can also serve as a guide for the needle insertion angle and direction, as the needle should be aligned parallel to the TPL and advanced in a cephalad direction.[1]

The aim of this study is to evaluate the feasibility and efficacy of ultrasound assisted TPL as a guide for lower thoracic and lumbar neuraxial blocks. This study hypothesizes that this technique will lead to a higher success rate of first-attempt needle placement compared to traditional palpation methods. We also anticipate that the of ultrasound assisted TPL technique will reduce the overall number of attempts needed for successful block placement.

           AIM

The aim of this study is to assess the efficacy of ultrasound-assisted TPL guidance compared to the traditional palpatory method in achieving first-attempt success in lower thoracic and lumbar neuraxial blocks.

 PRIMARY OBJECTIVE

The primary objective of this randomized controlled trial is to compare the first-attempt success rates of lower thoracic and lumbar neuraxial blocks performed using ultrasound-assisted TPL guidance versus those performed using the traditional palpation method.

SECONDARY OBJECTIVES:

The secondary objectives of the study are designed to further explore the implications of using ultrasound assistance for neuraxial blocks beyond the primary measure of first-attempt success rate. These include:

1)     Number of Attempts: This refers to the total number of times the needle is inserted through the skin with the intention of reaching the neuraxial space. Each new penetration of the skin after withdrawal of the needle constitutes a new attempt.

2)     Number of Needle Redirections: This denotes the number of times the direction or angle of the needle is adjusted while it remains under the skin, in an attempt to correctly position it within the neuraxial space.

3) To identify association between depth of neuraxial space and depth of transverse process.

METHODOLOGY

Study Design

This will be a prospective, randomized, controlled trial. The patients undergoing lower thoracic and lumbar neuraxial blockade for surgical anaesthesia or pain management at our institution will be included over a 12-month period.

Study Setting

The study will be conducted in the Department of Anesthesiology, Pain Medicine and Critical Care, All India Institute of Medical Sciences New Delhi.

Study Population

The study population will consist of adult patients who are scheduled for elective surgery under lower thoracic and lumbar neuraxial block.

Inclusion Criteria:

1.     Adult patients (age ≥ 18 years)

2.     Patients scheduled for lower abdominal, pelvic, and lower extremity surgeries under lower thoracic and lumbar neuraxial block.

3.     Patients of American Society of Anesthesiologists (ASA) status 1 or 2

4.     BMI < 35kg/m2

Exclusion Criteria:

1. Refusal by Patients
2. Previous thoracic or lumbar spine injury
3. Existing spine deformity
4. Known allergy to local anaesthetics.
5. Local site infection
6. Bleeding diathesis

  Sample Size Calculation

The study by Pakpiron, J et al demonstrated a first-pass success rate of 35.4% with palpation technique and 68.8 % with ultrasound guidance.[4] The sample size is calculated to test the hypothesis that ultrasound assisted transverse process line guidance is superior to palpatory method for first attempt success during central neuraxial block with the superiority margin (δs) set at 0.05. It is thereby estimated that a sample size of 80 (40 patients per study group) will provide 80% power to demonstrate the difference in first attempt success rate between the two techniques with an α error of 0.05 and taking into consideration 10% drop out rate.

Recruitment and Consent

Patients meeting the inclusion criteria will be approached by the research team during pre-operative assessment. The research team will explain the study’s purpose, procedures, potential risks, and benefits in detail. Written informed consent will be obtained from all participants before inclusion in the study.

Randomization and Blinding

Participants will be randomly assigned to one of two groups: the ultrasound assisted TPL guidance group (Group U) or the traditional palpation method group (Group P). Randomization will be done using computer-generated random numbers to ensure equal allocation. Blinding will not be possible due to the nature of the procedure.

Study Procedure

After shifting the patient inside the operating room, patient monitoring will be done as per ASA standards. Baseline values of pulse rate, non-invasive blood pressure (NIBP), oxygen saturation will be recorded. Intravenous line will be secured with an appropriate size cannula.

 Ultrasound-Assisted TPL Guidance Technique (Group U)

1. Preparation:  Patients will be positioned in sitting position. The ultrasound machine with a low-frequency curvilinear probe (2-5 MHz) will be prepared, and the skin sanitized.

2. Ultrasound Scanning: The probe will be positioned in a parasagittal plane approximately 4-5 cm from the midline to visualize the shadow of the kidney. It will then be shifted cranially to capture the acoustic shadow cast by the 12th rib. Subsequently, the probe will be moved medially along the 12th rib to locate the T12 transverse process (the "trident sign"). Measurements will be taken to determine the depth of the transverse process from the skin and its proximity to the midline.

3. Marking: A horizontal line will be drawn from the identified transverse process towards the midline, marking the needle insertion point based on the intersection with the midline.

4. Needle Insertion: Under sterile conditions, the neuraxial block needle will be inserted at the marked point, with slight cephalad angulation, aiming for the epidural or subarachnoid space as clinically indicated.

Failure: In case of failure in three attempts, senior experienced anaesthesiologists will be

called for help and will be noted.

 Landmark Identification for the traditional palpatory method (Group P )

Using palpation, landmarks such as the iliac crest and spinous processes are identified to determine the appropriate interspinous space for needle insertion.

Needle Insertion: The needle is inserted using the loss of resistance technique or feeling for the epidural space without ultrasound guidance. The anaesthesiologist uses tactile feedback to guide the needle to the intended space. In case of spinal anaesthesia, needle is inserted in the intervertebral space till free flow of cerebrospinal fluid (CSF) is observed.

 Parameters Measured

1. Demographic Data: Age, gender, weight, height, body mass index (BMI), and clinical indication for the neuraxial block.

2. Procedural Data:

a.      Type of neuraxial block – epidural or intrathecal

b.     Depth of the transverse process from the skin in cm [ST]

c.      Needle insertion depth to achieve neuraxial space in cm [SN]

d.     Difference (SN-ST) in mm.

e.      Number of attempts to successful block placement.

f.      Number of redirections at the same entry point.

g.     Duration of the procedure (time from skin puncture to successful block confirmation).

 3.     Outcomes:

a.      Primary: Comparison of first attempt success rate between the groups U and P

b.     Secondary:

i.     Comparison of both groups in terms of:-

-        Number of needle insertions sites

-        Number of needle redirections at one insertion point

-        Duration of procedure

ii.     To find association between depth of neuraxial space and depth of transverse process.

 Data Collection

Data will be collected using a standardized proforma and entered to a secure electronic database. The proforma will include sections for each of the parameters listed above, with additional space for notes on any unexpected findings or procedural deviations.

Data Analysis

SPSS version 23 (IBM Corp., Chicago, IL, USA) will be used for data analysis. The normality of the data will be checked using Kolmogorov-Smirnov and Shapiro-Wilk tests of normality. Data will be represented as Mean ± Standard deviation or in frequencies. Qualitative data will be compared by applying Chi square or Fisher test wherever necessary. Quantitative data will be compared by Student t test. P value of < 0.05 will be considered as significant variable.

Institutional Ethics Committee Clearance

The study would be done once the ethical committee passes the proposal.

REFERENCES:

1. Santhosh SA, Bhoi D, Thangavel K, Soni L. Ultrasound-assisted transverse process line as a guide for performing lumbar neuraxial block. Saudi J Anaesth. 2023 Jan-Mar;17(1):133-5. doi: 10.4103/sja.sja_462_22. Epub 2023 Jan 2. PMID: 37032682; PMCID: PMC10077786.

 2. Perlas A, Chaparro LE, Chin KJ. Lumbar Neuraxial Ultrasound for Spinal and Epidural Anesthesia: A Systematic Review and Meta-Analysis. Reg Anesth Pain Med. 2016;41(2):251-60. DOI: 10.1097/AAP.0000000000000184.

 3. Karmakar MK, Li X, Kwok WH, Ho AM, Ngan Kee WD. Sonoanatomy relevant for ultrasound-guided central neuraxial blocks via the paramedian approach in the lumbar region. Br J Radiol. 2012 Jul;85(e262-e269). DOI: 10.1259/bjr/93508121.

 4 Pakpirom J, Thatsanapornsathit K, Kovitwanawong N, Petsakul S, Benjhawaleemas P, Narunart K, Boonchuduang S, Karmakar MK. Real-time ultrasound-guided versus anatomic landmark-based thoracic epidural placement: a prospective, randomized, superiority trial. BMC Anesthesiol. 2022;22:198. doi: 10.1186/s12871-022-01730-5.