The subarachnoid block is a safe and effective alternative to general anaesthesia when the surgical site is on the lower abdomen, perineum, or lower extremities. Spinal anaesthesia is  the preferred regional technique for caesarean section due to its ease of administration with a high success rate and rapid onset of anaesthesia. Spinal anaesthesia for caesarean section is commonly delivered using the traditional landmark technique where we palpate bony anatomical landmarks i.e the iliac crests and spinous processes to locate the L4-L5 intervertebral space.

The proposed ideal site for spinal anaesthesia is below the Conus medullaris. In adults, Conus  medullaris ends at the lower border of the body of L1 vertebrae in the majority of the population. It has been reported that there is an increased incidence of neurological trauma following spinal anaesthesia if performed at the vertebral level where conus medullaris ends. Neurological trauma is seen more in the obstetric population due to the variation in normal anatomy that occurs during pregnancy. Variations in the normal anatomy of the vertebral column in pregnancy can also make it difficult for anaesthesiologists in locating the intervertebral space. The physical changes that occur in pregnancy are-

1)Lumbar lordosis

2)Rotation of pelvis to the long axis of the spinal column

3)Weight gain

All of the above would lead to difficulty in estimation of intervertebral space via landmark technique. The advantages of ultrasound guidance over conventional techniques include the ability to both view the targeted structure and visualize, in real-time the distribution of the injected medication, and the capacity to control its distribution by readjusting the needle position if needed. USG guidance should plausibly improve the success rate of the procedures, their safety and speed. For locating the L4 L5 intervertebral space, USG of the spine appears to help increase the success of the subarachnoid block. It is non-invasive and hence will be safe for pregnant women, radiation-free and known to her from early on in pregnancy. In this study, we are going to assess if a USG-assisted technique could reduce the time taken for the procedure, number of needle passes required for identifying subarachnoid space and if there is any correlation with post- dural puncture headache using the USG technique when compared to landmark guided  technique in pregnant women.

After approval from the Institutional Ethics committee and with informed and written consent, pregnant women who will undergo landmark guided technique will be considered as group L and the ones who will undergo ultrasound-guided technique will be considered as group U.

Procedure-related definitions are given below:

1.Preparation time: the time taken by the anaesthesiologist from palpation the of iliac crest or placement of ultrasound probe over the back till the needle insertion.

2.Procedural time: the time taken from the insertion of the spinal needle until the free flow of CSF

3.Success rate: Obtaining CSF flow.

4.Attempts: insertion of a spinal needle into the skin

5.Passes: redirecting the spinal needle in the same space or different space without exiting the skin.

6. Patient satisfaction score: At the end of the surgery, patients will be queried for satisfaction and made to mark intraoperative anaesthetic satisfaction on a four-point Likert scale (1 – Not satisfactory, 2 – Satisfactory, 3 – Good, 4 – Excellent) based on the number of needle pricks, pain at the site of injection, intraoperative analgesia, and sedation

7. Post dural puncture headache: Bilateral frontal or occipital headache that is worse in the upright position, along with nausea, neck pain, dizziness, visual changes, tinnitus, hearing loss, or radicular symptoms in the arms.

8.Distance from the skin to subarachnoid space- measurement of the distance from the skin to the ventral border posterior complex on the ultrasound or length of the needle inside the body on successful attempt as measured using a scale after spinal anaesthesia

Standard fasting protocols will be followed in all the patients. Intravenous cannulation will be  established and oral premedication with a tab. Pantoprazole 40mg would be given on the previous day and before the procedure. Patients would then be shifted to the operating room  in the left lateral position. Inside the operation theatre, standard monitoring in the form of non-invasive blood pressure, electrocardiogram, and pulse oximetry will be instituted and the baseline parameters will be recorded. All participants, after noting down baseline parameters, will be made to lie in the left lateral decubitus position, in group L under aseptic precautions L3-L4 or L4-L5 intervertebral space will be identified using the landmark technique by palpating the space that corresponds to Tuffier’s line, and in this space, local infiltration will be given, after this spinal anaesthesia will be administered. In group U, a sterile cover will be applied to the curvilinear USG probe. A parasagittal view of the spine will be obtained, and then the L3–L4 intervertebral space will be identified by moving up from the sacrum below. At this selected L3–L4 intervertebral space, the probe position will be changed to a transverse view and brought to the midline. After identifying the L3–L4 space, the best image of the anterior complex and posterior complex will be obtained, and a sterile surgical skin marker will be used to mark the midpoint of the long and short borders of the probe in the midline. The point of intersection between the two perpendicular lines will be identified as the point of entry. Then local infiltration and spinal anaesthesia will be given at the marked point. Conventionally trained anaesthesiologists who are experienced in identifying posterior cord structures using ultrasound will be performing the procedure. In both groups, the procedural time, preparation time, number of attempts in the same space and different spaces, number of passes, distance of subarachnoid space from the skin, patient satisfaction score will be measured. The dosage of local anaesthetic will be kept standard between the groups as 10mg of 0.5% hyperbaric Bupivacaine. In both groups, the primary outcome will be the success rate. The secondary outcomes will be the time taken to administer spinal anaesthesia,the distance from the skin to subarachnoid space, patient satisfaction and occurrence of post-dural puncture headache. At the end of the surgery, patients will be queried for satisfaction and made to mark intraoperative anaesthetic satisfaction on a four-point Likert scale. Patients will be followed up for 7 days, if patient is discharged before completion of 7 days, a follow up till the 7^th day will be done via telephone.