CONTEXT AND OBJECTIVE: Controversies exist regarding the site of action of Fentanyl after epidural injection. The objective of this investigation was to compare the analgesic effect of epidural and intravenous Fentanyl for lower limb orthopedic surgeries.

DESIGN AND SETTING: A randomized and double-blind study was performed in Hospital São Paulo.

METHODS: 29 patients were divided into two groups. During the postoperative period, in the presence of pain, group 1 (n = 14) patients received 5 mL of a 100 mcg Fentanyl solution in saline without preservative by the epidural route and 2 mL saline intravenously. Group 2 (n = 15) patients received 5 mL saline by the epidural route and 2 mL (100 mcg) Fentanyl intravenously. Analgesic supplementation consisted of 40 mg intravenous Tenoxicam and 5 mL epidural 0.25% bupivacaine (if pain relief was not achieved with Tenoxicam). Pain intensity was evaluated by numerical scale and plasma concentrations of Fentanyl were measured simultaneously.

Inclusion Criteria:

• Both genders ranging in age from 18 to 65 years, American Society of Anesthesiologists (ASA) Physical Status 1 or 2, scheduled for orthopedic bone surgery of the lower limbs

Exclusion Criteria:

• Patients with infection in the puncture area and coagulation disorders, pregnant patients, and patients using opioids