Performance of regional anaesthesia under ultrasound guidance has gained popularity worldwide because of the easily performed procedure, confirmation of landmarks and deposition of local anaesthetic at correct place. Studies have shown that placement of epidural needle using LOR technique can be inaccurate in upto 30% of lumbar epidural blocks. The reason is because of high variability in distance between the skin and epidural space and the anatomical structures that can hinder appropriate identification of epidural place. According to a study done by Chin KJ et al. in patients with difficult surface anatomical landmarks showed the success of performing central neuraxial blockade was twice after a pre-procedural ultrasound as compared to manual palpation. According to a study done by Park SK et al. and Geng J et al., the ultrasound guided CSE anaesthesia technique provide increased precision and efficacy of performing central neuraxial blocks in elderly patients. The most common complaint of epidural block with or without catheter insertion is inadequate pain relief. The rate of failed epidurals range from 1.5 to 20% depending on the experience of the anaesthetist and/or the institution. In a study done by Bo Qu et al, it was found that ultrasound assisted CSE anaesthesia increases first-pass and first-attempt success rates and also reduce needle insertion attempts, passes, and puncture time for elderly population with hip fracture, especially those with scoliosis. Furthermore, Mehmut Canturk et al. in his study done on non-parturient patients on estimation of epidural depth using TMP and PSO view on ultrasound found that both the planes provide reliable estimates for actual epidural depth. Paramedian approach is preferred in elderly population for access to central neuraxial blockade in elderly patients because of certain age-related anatomical changes of the vertebral structures and ligaments. Therefore, considering the efficacy of ultrasound in assessment of epidural space, present study has been planned to compare the epidural depth measured using preprocedural ultrasound using two views i.e. median transverse plane view and paramedian sagittal oblique view in elderly patients.

After an approval from the institutional review board, the study will be approved by Institutional Ethics Committee. Written informed consent will be obtained from all patients. This prospective observational study is prepared in accordance with the Declaration of Helsinki and strengthening the reporting of observational studies in epidemiology (STROBE) guidelines. Patients meeting the inclusion criteria of either gender will be enrolled. Demographic data of the patients (age, height, weight, body mass index, ASA physical status) will recorded and standard ASA monitoring will be done.  An intra-venous line will be secured for intravenous medication and hydration. All patients undergo US scanning in the sitting position with their knees, hips, the neck and lower back flexed. The patient position will be same during the US assessments and the CSE procedure. All US scannings will be done by anaesthestist with a 2–5 MHz curved array probe before the CSE procedure under non-sterile conditions for each patient at the L3–4 intervertebral space. The US scanning will start initially in PSO at the sacral region to visualise the hyperechoic continuous line of the sacrum and then the curved array probe will be moved 2–3 cm laterally to mid-line and tilted medially to capture the PSO view image of the vertebral canal. In the PSO plane, the sacrum, spinous processes, ligamentum flavum, posterior duramater, cauda equina and anterior duramater would be visualised as hyperechoic structures; and subcutaneous tissue, muscle layers, epidural space and intrathecal space as hypoechoic structures. The US probe will then be moved cephalad until the L3–4 intervertebral space would be cantered. At this point, the monitor will be frozen for further measurement of skin-to-epidural depth with the built-in calliper of the US device in millimetres. The skin will be marked on both sides of the probe at midline to identify the level of L3–4 intervertebral space in the horizontal plane. After completion of ED measurements in PSO (ED/ PSO), the probe will be rotated to TM on the predetermined horizontal line at the L3–4 intervertebral space. The curved array probe will be moved cephalad or caudad to visualise the spinous process. Once the spinous process is identified, the skin will be marked on both sides of the probe in the midline. The skin marks will be elongated as a vertical line to determine the midline. With the completion of the US assessments, the skin will be prepared aseptically, and a sterile drape will be wrapped on the back of the patient. The skin and subcutaneous tissue will be infiltrated with 5 ml 2% lidocaine. The anaesthesiologist per-forming CSE will be blinded for the ED but will be informed about the insertion point for the epidural needle. The loss of resistance to the air technique with a midline approach at the L3–4 intervertebral space will be used to identify the epidural space in all patients. The epidural needle will be marked with a sterile marker following the identification of epidural space and the spinal needle w introduced to intrathecal space with the needle-through-needle technique. With the observation of free-flowing clear cerebrospinal fluid, appropriate volume of 0.5% hyperbaric bupivacaine will be injected into the intrathecal space, and the spinal needle will be withdrawn. The epidural catheter will be located 5 cm into the epidural space, and the epidural needle will be removed. The AED will be measured with a linear scale starting from the tip of the epidural needle to the sterile marker in millimetres.