The main objectives of the trial are the efficacy and safety of intercostal nerve block in the midaxillary line versus paravertebral block, both guided by ultrasound in patients scheduled for not reconstructive breast surgery.

Inclusion Criteria:

1. Patients scheduled for not reconstructive unilateral breast surgery.
2. Physical status American Society Anesthesiologists (ASA) I-III.
3. Signed informed consent.
4. Aged between 18 and 75 years.
5. Ability to assess pain using a verbal and numerical scales.
6. Assessment of pain at the time of inclusion in the study is lower than 3 verbal simple scale

Exclusion Criteria:

1. Personal history of disorders of hemostasis or previous history of abnormal bleeding evidence.
2. Local infection at the site of the puncture or to puncture prior systemic.
3. Contraindications to study medication.
4. Muscle or neurological disease, peripheral or central.
5. Patients with prior history of opioid.
6. Pregnancy or lactation.
7. Difficulties in assessing pain or inability to understand or assist in the development of the study (psychiatric illness, cognitive impairments)
8. Active Chronic alcoholism or drug addiction.
9. BMI under 20 or mayor 30.
10. Chronic treatment with non-steroidal anti-inflammatory drugs, antidepressants, anticonvulsants or opioids.
11. Rejection of the patient