This prospective, randomized study will be conducted in the Department of Anaesthesiology, Dr. S. N. Medical College and Attached Group of Hospitals, Jodhpur. The patients will be randomly selected from the patients posted for elective modified radical mastectomy, under general anaesthesia after confirming all inclusion and exclusion criteria. A written informed consent will be taken from all the patients for performance of block after complete explanation about the study protocol, anaesthetic technique, merits and demerits of the procedure in perioperative course of anaesthesia.

Preoperative evaluation and preparation: All selected patients will be undergo a routine pre-anaesthetic check-up (PAC), including explanation of numeric rating scale (NRS) ^[19] pain scale (0-10, where 0 stands for no pain and 10 stands for worst imaginable pain) for post-operative pain assessment. All the patients will be kept nil per oral as per the fasting guidelines. All patients will be premedicated with tab alprazolam 0.5 mg orally night before the surgery.  In the operative room, identification of patient, fasting status, consent and PAC will be confirmed. After reassuring the patient, standard ASA monitoring will be applied. Base line heart rate (HR), non- invasive systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean blood pressure (MAP), respiratory rate (RR), and peripheral oxygen saturation (SpO₂) will be recorded. Continuous electrocardiographic (ECG) monitoring will be done. Peripheral i.v. cannulation will be done by using 18G cannula in the contralateral upper limb and lactated ringer’s solution will be started.

Method of ESP block:-The block will be performed on the side of surgery with the technique used by Forero M and colleagues ^[38]. The patient will be placed in a sitting position and a high frequency linear ultrasound transducer will be placed in a longitudinal orientation 3 cm lateral to T3 or 4 spinous process. Trapezius, rhomboid major and erector spinae muscles will be identified, superficial to the hyperechoic transverse process shadow and a 10 cm, 22 G block needle will be inserted until the tip crosses the interfacial plane between rhomboid major and erector spinae muscle, and reaches the transverse process, evidenced by visible linear spread of fluid upon injection. After negative aspiration, 20 ml of 0.25% levobupivacaine will be injected.

Method of Pectoral Block:-In Group P PECS block will be performed on the side of surgery after informed consent and application of standard monitoring. The patient will be placed in supine position with the arm abducted (block side). The area will be prepared with 5% povidone iodine solution and covered with sterile drapes. Skin will be infiltrated with 2% lignocaine. The USG probe will be placed at midclavicular level inferolaterally to locate the axillary artery and vein, and then moved laterally until pectoralis minor and serratus anterior muscles will be identified at 3^rd rib level. After identification of muscle layers, the needle will be advanced in the plane of probe from medial to lateral in an oblique manner until the tip enters the plane between pectoralis minor and minor serratus anterior muscle, 20 ml of levobupivacaine deposited. After deposited the drug in between pectoralis minor and serratus anterior muscle, the needle will be withdrawn till it lies in the potential space between pectoralis minor and pectoralis major. After negative aspiration 10 ml of levobupivacaine deposited in this space.

After performing the block, the patients will be observed in pre-operative room for 30 min. The sensory level of block will be assessed with pin prick method every 5 min till 30 min. Total number of dermatomes that has less pain to pin prick compared with opposite side will be noted. If pin prick sensation does not decrease, then it is considered as block failure. Any side effect in form of nausea, vomiting, respiratory depression, hypotension, and pruritus and chest pain will be noted. Respiratory depression is defined as respiratory rate less than 8 breath/min or SpO₂ <90% after 30 min of block, patient will be shifted to the operating room.

Anaesthesia technique:-The general anaesthesia will be induced with injection fentanyl (2 μg/kg) and propofol (1.5 mg/kg). The endotracheal intubation will be facilitated by using muscle relaxant inj. vecuronium bromide (0.1mg/kg) after confirming adequacy of ventilation and loss of consciousness. The airway will be secured with appropriate size of endotracheal tube. The anaesthesia will be maintained with air oxygen (50:50), isoflurane and injection vecuronium bromide. Supplemental analgesia will be providing with injection fentanyl (1 μg/kg) when rise in HR or MAP more than 20% of base line values. 

Continuous monitoring of HR, NIBP, SpO₂ and end tidal carbon-dioxide (EtCO₂) will be done throughout intra operative period and recorded every 15 min. The EtCO₂ will be maintained between 35-40 mm Hg. The number of doses and total amount of supplement analgesia intra operative with fentanyl will be recorded for comparison between two groups. Fifteen min before surgery completion ondansetron 8 mg i.v. given and residual neuromuscular blockade will be reversed with neostigmine 0.05 mg/kg and glycopyrrolate 0.01 mg/kg i.v. and the trachea will be extubated when the patient is fully awake and breathing adequately. The patients will be shifted to the recovery room for further management. The total duration of the surgery will be also recorded.

Post operatively patients will be given morphine 3 mg i.v. as rescue analgesia, if NRS ≥4.  HR, NIBP, SpO₂, RR and NRS score will be recorded at 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22 and 24 h after the surgery. Time to first rescue analgesia as well as the total doses of morphine used in first 24 h will be recorded. Any side effects like nausea, vomiting, respiratory depression, hypotension, pruritus and chest pain will be recorded and will be treated accordingly. The patient’s satisfaction score will be noted. Nausea lasting more than 10 min or vomiting will be treated with ondansetron 4mg i.v.

Postoperative observations:-

The following characteristics of the block will be observed postoperatively:

1. Duration of analgesia: Duration of analgesia will be defined as the time interval from completion of local anesthetic administration till first need of rescue analgesic. The rescue analgesic regime morphine 3 mg i.v. slowly as analgesic whenever NRS ≥ 4 or on request.

 2. Pain assessment: The numerical rating scale (NRS) is a segmented numeric version of the visual analog scale (VAS) in which a respondent selects a whole number (0–10 integers) that best reflects the intensity of his/her pain. The common format is a horizontal bar or line which contains 11-point numeric scale ranges from ’0’ representing one pain extreme (e.g. “no pain”) to ’10’ representing the other pain extreme (e.g. “pain as bad as you can imagine” or “worst pain imaginable”). NRS for pain will be assessed during rest (NRS-R) and movement (NRS-M) at predefined intervals at 0, 2, 4, 6, 8, 10, 12, 15, 18, 21 and 24 h postoperatively. 

3. Total rescue analgesic consumption: The total dose of morphine used in initial 24 h.

4. Postoperative side effects or complications: Local anesthetic toxicity, nausea, vomiting, pruritus, drowsiness, convulsions etc.

 5. Hemodynamic and respiratory changes: Bradycardia (pulse <50 beats/min), hypotension (reduction of MAP >20% of baseline), respiratory depression (RR ≤8 breaths/minute or SpO2< 90%).

 6. Patient’s satisfaction score:    4 = excellent, 3 = good, 2 = fair, 1 = poor.