This is a comparative study will be planned to initiate after obtaining approval from Institutional Ethics Committee and informed consent from all patients. 

Following a detailed pre anesthetic examination, total 72 patients of American society of Anaethesiologists(ASA) I and II, aged 18-60 years, posted for elective abdominal surgery fulfilling the inclusion criteria will be allocated for this study. They will be randomly divided into two equal groups. Group T -36  ESP block with injection bupivacaine 0.25 percent and Group R -36  LAI with injection bupivacaine 0.25 percent. Randomization will be ensured by an informatically generated random sequence run by a person who will not involved in the study. During preoperative visit, all the patients will be explained about the 100 mm visual analog scale (VAS). 

All the patients will be advised tablet diazepam (5mg) at the night before OT. In preoperative area intravenous ringer lactate solution will be started at 100ml/h and a standard anaesthetic protocol will be followed for all patients. All the standard ASA monitor like Electrocardiogram(ECG), SPO2, pulse oximetry, capnometer, blood pressure monitor and temperature monitor will be attached with patient for continuous monitoring.

Baseline values are noted before anaesthesia for all patients and will receive general anaesthesia according to a standard protocol with ASA monitoring. 

After securing IV line with an 18G cannula. Intravenous(IV) induction will be done with Inj. Fentanyl (2 mcg/kg), Inj. Loxicard (1 mg/kg), Inj. Propofol (2 mg/kg) and Inj.Atracurium (1mg/kg) will be administered for endotracheal intubation (ET). Patients will be maintained with N2O and O2 mixture in 1:1 ratio, inhalational isoflurane 0.5-1% to maintain bispectral index <50 and Inj. Atracurium (0.5 mg/kg) will be administered if TOF count more than 0.4. Intraoperative pulse rate (PR), Blood pressure (BP), oxygen saturation (SPO2) will be noted at 30 min interval till the end of operation for the surgery of duration 2 - 2½ hrs.

Intra operatively whenever there will be increase in BP and Heart Rate (HR) by more than 20% from pre-operative baseline value, will be treated with intravenously IV Fentanyl bolus 1 mcg/kg . Before reversal of neuromuscular block, the group LAI group patients will be infiltrated with 20 ml of 0.5 % bupivacaine by subcutaneous infiltration ( maximum 0.4 ml/kg) by the operating surgeon. 

On the other hand, ESPB group will receive the block in lateral position at the end of operation before reversal. Ultrasound guided linear or convex probe will be used depending on the depth of transverse process. A 22G x 80 mm needle used for ESPN block. For parasagittal view probe will be placed longitudinally beside the spine. The needle will be directed towards medial transverse process of mid level vertebra. When the needle comes to the contact with the transverse process, 20 ml 0.25% bupivacaine will be injected on either side of target vertebra. After this, all the patients will be reversed with IV Myopyrolate 5 ml (0.5 mg Glycopyrrolate and 2.5 mg neostigmine). After extubation, patient will be shifted to recovery room and when the patient will be stabilized (alderate score more than 9), all the patient transferred to Surgical ICU for immediate 24hrs after operation. 

Patient, investigator and statistician all will be remain blinded regarding the type of block. Postoperatively analgesia will be assessed with Visual analog scale (VAS) at 0, 1, 2, 3, 4, 5, 6, 10, 14, 18, 22 and 24 h. Intravenous paracetamol (15mg/ kg) 8 hourly will be administered as baseline analgesic. IV tramadol 2mg/kg will be administered if VAS score more than 4. The timing of first analgesic requirement will be considered as duration of analgesia. 

Postoperative hemodynamics (PR, BP) will also be noted at 0, 1, 2, 3, 4, 5, 6, 10, 14, 18, 22 and 24hrs. Duration of analgesia and postoperative total IV tramadol requirement will be considered as primary outcome. Patient satisfaction will be assessed by likert scale at 24 hours after surgery. Postoperative hemodynamics and any adverse effect like nausea, vomiting, sedation will be considered as secondary outcome.