Comparison of local anesthetic agents, ropivacaine and levobupivacaine, for ultrasound-guided nerve blocks

INTERVENTION: Ropivacaine is adminitered for ultrasound‐guided nerve blocks. Levobupivacaine is adminitered for ultrasound‐guided nerve blocks. CONDITION: diseases that require surgery in the upper and lower extremities PRIMARY OUTCOME: Time required for onset of sensory and motor blocks and duration SECONDARY OUTCOME: Quality of anesthesia and amount of analgesics administered during surgery, percentage of patients requiring general anesthesia, and postoperative complications. INCLUSION CRITERIA: Patients undergoing surgery in upper or lower extremities.