Comparative Study of Ultrasound Guided Superficial vs Intermediate Cervical Plexus Block for Perioperative Analgesia in Thyroid Surgeries.

• Ultrasound guided superficial cervical plexus block (Procedure): Ultrasoundguided subcutaneous superficial cervical plexus block. The linear probe will be placed transversely over the lateral side of the neck at the midpoint of the posterior border of the sternocleidomastoid muscle (SCM) such that the tapering end (posterior border on the ultrasound image) of the SCM comes to the center of the screen. After infiltrating the skin with 1 mL of 2% lignocaine, the needle will be introduced from the posterior aspect through the skin and platysma where 10 mL of 0.25% bupivacaine with 5 µg/mL of epinephrine (50 µg) and 100 µg dexmedetomidine (with concentration of 200µg/2ml) diluted in 2 ml saline) will be deposited just behind this landmark to give a single point subcutaneous superficial cervical plexus block. Block will be repeated on the other side as well
• ultrasound guided intermediate cervical plexus block (Procedure): The transducer probe will be placed transversely over the midpoint of the sternocleidomastoid muscle such that the tapering posterior edge was positioned in the middle of the screen (at the level of the cricoid cartilage, where the external jugular vein crosses sternocleidomastoid). With the in-plane technique, after infiltrating the skin with 1 mL of 2% lignocaine, the block needle will be advanced adjacent to the superficial cervical plexus in the plane deep to sternocleidomastoid, underneath the investing fascia (sternocleidomastoid-trapezius fascia) and immediately above the interscalene groove \[Figure 3\]. After negative aspiration, 10 mL of 0.25% bupivacaine with 5 µg/mL of epinephrine (50 µg) and 100 µg dexmedetomidine (with concentration of 200µg/2ml) diluted in 2 ml saline) will be deposited under the fascia after feeling the click or 'pop' on piercing this fascia. The same formulation will be given on the other side as well.

Primary outcomes

• Postoperative VAS scores [VAS scores at 0 (just after extubation), 2, 4, 6, 12, 18 and 24 hours.]: The postoperative VAS scores at 0 (just after extubation), 2, 4, 6, 12, 18 and 24 hours.

Secondary outcomes

• Total dose of rescue analgesic required [first 24 hours]
• Diaphragmatic excursion measured by ultrasound M-mode [30 minutes after the block and after endotracheal extubation]

Sex: All, ages: 20 Years to 60 Years

Inclusion Criteria:

* Patients with ASA physical status 1 or 2 and 3
* Patients undergoing elective total thyroidectomy (with normal thyroid function tests)
* Patients aged 20 to 60 years of both sexes

Exclusion Criteria:

* Patients with known bleeding diathesis
* History of allergy to local anaesthetics or known diaphragmatic motion abnormalities
* Patient who refuse to participate
* BMI (Body Mass Index) more than 35 kg/m2
* Previous neck surgeries/Burns injury to neck/ contractures in neck
* Patients with known seizure disorder
* Patients with history of radiation exposure on neck.