The advent of ultrasound made possible greater safety and the creation of new peripheral blocks that aim to reduce the morbidity of the anesthetic technique on the cancer patient. Pectoral nerve block (PEC Block) is technically simple and easily reproducible. Inspired by the infraclavicular approach, it aims at the anesthesia of the pectoral, intercostobrachial, intercostal III-IV-V-VI nerves and the long thoracic nerve 8 being a safe, reproducible technique with little discomfort for the patients, with few complications and allowing a good control of acute pain.

The hypothesis is that the realization of pectoral nerve block provides a good alternative to epidural or paravertebral block with a lower risk for the patient and that is shown as an optimal anesthetic option with reduction in postoperative pain, anesthetic and opioid consumption. Main objective is the evaluation of postoperative pain through opioid consumption in the first 24 hours postoperatively.

Patients will undergo a prospective, randomized, single blind, placebo controlled study in which the examiners responsible for the postoperative evaluation will not know which of the two groups were randomly assigned: 40 patients in the Control and 40 patients in the PECS Group . Patients will be randomized through a list generated by www.randomizer.org into two groups.

Patients will receive standard monitoring, pre-anesthetic medication with midazolam 0.05 mg / kg EV. All patients will receive balanced general anesthesia with fentanyl 2 mcg / kg, lidocaine 2 mg / kg, propofol 1-2 mg / kg, cisatracurium 0.15 mg / kg or Rocuronium 0.6 mg / kg. The PECS II group will receive an injection of 20mL of 0.5% Ropivacaine between the serratus and the smaller pectoralis and 10mL of 0.5% ropivacaine between the pectoralis major and minor muscles with the aid of ultrasonography. Maintenance of anesthesia in the two groups: general anesthesia balanced with sevoflurane (with and fraction expired from 1 to 3%, to maintain BIS between 40 and 60). Prophylaxis for postoperative nausea and vomiting will be performed with slow intravenous administration following the anesthetic induction of Dexamethasone 4 mg, and at the end of the surgery slow intravenous administration of Ondansetron 4 mg. At the end of surgery, patients in both groups will receive Dipyrone 2 g and Parecoxib 40 mg. Patients will be evaluated in the postoperative times: T1: arrival at the PACU, T2: 3 hours postoperatively or discharge from the PACU), T3: 12 hours postoperative, T4: 24 hours postoperative.

• Drug: sevoflurane and fentanil
  Patients will receive standard general anesthesia
  Other Name: Standard general anesthesia
• Drug: sevoflurane and fentanil plus PECS II block
  Pacients will receive standard general anesthesia with sevoflurane and fentanil associated to PECS II block
  Other Name: Standard general anesthesia plus PECS II block

• Placebo Comparator: Placebo group
  Patients in placebo group will receive general balanced inhaled anesthesia with sevoflurane and fentanil
  Intervention: Drug: sevoflurane and fentanil
• Active Comparator: PECS II group
  Patients in PECS II group will receive general balanced inhaled anesthesia with sevoflurane and fentanil
  Intervention: Drug: sevoflurane and fentanil plus PECS II block

Inclusion Criteria:

• Female patients, aged 18 to 60 years, electively scheduled to perform mastectomy in the Base Hospital of the Federal District;
• Physical State 1, 2 or 3 the American Society of Anesthesiology (ASA);

Exclusion Criteria:

• Patients with unstable angina
• Patient with poorly controlled asthma
• Substance abuse
• Heart failure, greater than first degree atrioventricular block
• Pregnant women
• Patients with allergy to dipyrone, morphine;
• Patients with chronic pain;
• Patients with severe hepatic disease;
• Patients with severe kidney disease;
• Patients with neurological diseases;
• Included patients in other clinical studies currently or in the past three months under general anesthesia;
• Patients who refuse to participate in the study;
• Any other condition that, in the opinion of the investigator, may pose a risk to the patient or interfere with the study objectives;