This project is one of four components of a thematic project that aims to evaluate the use of ultrasound in regional blocks, called "Use of ultrasound in regional blocks and injections for the treatment of acute and chronic pain."

It will evaluate quantitative and qualitative control of ischemic pain in the lower limbs in patients with peripheral arterial occlusive disease through continuous sciatic nerve block by perineural catheter, popliteal approach, compared to systemic analgesia based on opioids.

BACKGROUND: Peripheral arterial occlusive disease (PAOD) commonly evolves with intense ischemic pain in the lower limbs, which is hard to control with systemic analgesics, and continuous regional anesthesia may be an alternative, with adequate analgesia and lower incidence of side effects.

OBJECTIVES: evaluate qualitative and quantitative pain control, incidence of adverse effects and operative results in patients with PAOD undergoing continuous anesthetic blockade of the sciatic nerve by perineural catheter compared to systemic analgesia based on opioids and adjuvant medications.

METHODS: It is a randomized clinical trial, covered for evaluators. It will include 56 patients with PAOD Fontaine IV, with pain by the presence of ulcerations located on foot. A group will be submitted to continuous regional anesthesia of sciatic nerve through perineural catheter and another group will have its pain control through patient controlled analgesia device with intravenous fentanyl. The primary dependent variable will be pain, through the numerical pain scale.

Inclusion Criteria:

• Patients older than 18 years old who have strong or moderate persistent ischemic pain in the lower limbs, due to peripheral artery occlusive disease, classified as Fontaine IV (pain at rest and presence of ulcer or gangrene).

Exclusion Criteria:

• Uncooperative patients, coagulation disorders, patients with liver failure, who have atrioventricular block second or third degree, who refuse to be submitted to peripheral nerve block, with systemic or procedure site local infection infection, peripheral or central neuropathy history, allergies to local anesthetics or to any of the drugs to be used in the study and difficulty in understanding the use of the PCA (patient-controlled analgesia) device and evaluation methods used in the study .