The aim of this randomised controlled and double-blind study, is to compare the effects of erector spinae plane (ESP) and thoracic epidural (TEA) blocks on peri-operative hemodynamics and analgesia in patients undergoing unilateral mastectomies due to malignancy.

Patients will be randomised into two groups as Group E (those who received general anesthesia after the erector spina plan block) and Group T (those who received general anesthesia after thoracic epidural block).

After the block skin conductivity (galvanic skin response - GSR), body temperature changes, sympathetic and sensory block levels, peri-operative hemodynamic data, postoperative pain scores and analgesic consumption will be recorded.

Inclusion Criteria:

• ASA(American Society of Anesthesiologist) physical classification I-III
• Patients undergoing unilateral mastectomies due to malignancy

Exclusion Criteria:

• Active infection at the intervention site
• History of coagulopathy or anticoagulant use (less time has passed before peripheral and central blocks)
• Major cardiac, pulmonary, renal and neurological diseases
• Autonomic neuropathy or use of drugs that affect autonomic function
• Patients with type 1 diabetes or insulin dependent type 2 diabetes over 10 years
• Allergic to local anesthetics;
• Patients who are uncooperative or have psychiatric problems
• Morbidly obese (body mass index > 35 kg/m2)