Following approval from the Institutional Ethical Committee, informed written consent will be taken from 64 patients of  American Society of Anaesthesiologists (ASA) Physical status class I/II undergoing elective thoracotomies. A thorough pre anaesthetic evaluation will be done 24 hours prior to the procedure.  On the day of surgery, a single anesthesiologist performs either erector spinae block or thoracic epidural anaesthesia. A radial arterial line and an 18 G IV cannula will be inserted and the patient is connected to standard monitors such as noninvasive blood pressure, electrocardiography (ECG), and pulse oximetry (SpO2).

Under standardized general anaesthesia protocol, patient will be preoxygenated with 100% oxygen and premedicated with ondansetron 0.1mg/kg, midazolam 0.02mg/kg,
glycopyrrolate 0.01mg/kg and analgesics like fentanyl 2mcg/kg is used and induced with propofol 2mg/kg and muscle relaxants vecuronium 0.1mg/kg. Then patients are going to be
intubated with double lumen endobronchial tubes of respective sizes and connected to mechanical ventilator. Double lumen endobronchial tubes will be kept insitu and extubation is done after 2 hours post-surgery.

After giving general anaesthesia, based upon computer generated randomized sequence, one group of patients will receive thoracic epidural and another group will receive erector
spinae block. Thoracic epidural catheter will be inserted under strict aseptic precautions. An 18 G Tuohy needle is inserted at T6/T7 intervertebral space to identify epidural space using the loss of resistance technique. 20G catheter is threaded 3–4 cm into the epidural space, test dose i.e. 2% lignocaine plus 1:1000 adrenaline 3ml is given after the negative aspiration for blood or cerebrospinal fluid, followed by a continuous infusion of 0.125% sensorcaine plus 2 micrograms per ml fentanyl given at the rate of 5 ml//hour till 48 h postextubation.

Ultrasound guided erector spinae block will be performed under the strict aseptic precautions. A high‐frequency linear ultrasound transducer 12Hz, is placed in a longitudinal
orientation 3 cm lateral to the T6 spinous process corresponding to the T5 transverse process. Three muscles trapezius (uppermost), rhomboids major (middle), and erector spinae (lowermost) are identified superior to the hyperechoic transverse process. Using in‐ plane approach an 18 G Tuohy needle is inserted in caudal–cephalad direction, until the tip
is deep to erector spinae muscle as evidenced by visible hydrodissection below the muscle plane, on injection of 5 ml of normal saline. A 20 G epidural catheter is threaded 3-4 cm in
cephalad direction, after the negative aspiration for blood, followed by continuous infusion of 0.125% sensorcaine plus 2 micrograms per ml fentanyl given at the rate of 5 ml/hour till 48 h post extubation.

Rescue analgesia will be given to patient if visual analog score is >4. First rescue analgesic given to the patient will be paracetamol 20 mg/kg dose. The second rescue analgesic will

be ketorolac 0.5 mg/kg dose diluted in normal saline and administered slowly.