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Intrathecal opioids routinely are administered to surgical patients to provide prolonged postoperative analgesia. This study evaluated the dose-response effects of intrathecal fentanyl in an elderly patient population undergoing lower extremity revascularization procedures.Surgical anesthesia was induced using a continuous spinal technique. No patient received perioperative antiemetics or opioids. Postoperatively, after complete regression of spinal anesthesia, patients received via the spinal catheter either 0, 5,10, 20,40, or 50 µg fentanyl. Blood pressure, heart rate, respiratory rate, oxyhemoglobin saturation, and visual analog pain scores were recorded approximately every minute for 15 min after study drug administration. After this Initial observation period, blood pressure, heart rate, respiratory rate, oxyhemoglobin saturation were recorded every 15 min for the next 2 h, then every 30 mln thereafter. A verbal analog pain score, with 0 equivalent to no pain and 10 the worst pain imaginable, was obtained with each set of vital signs. The study was concluded when the verbal analog pain score was ≥3, the patient was medicated, and the time was recorded. Any side effects, such as respiratory depression, nausea, vomiting, and pruritus, were recorded.Minimal analgesia was derived from the 0-, 5-, and 10-µg doses. Beginning at 20 µg, patients experienced the onset of satisfactory analgesia (visual analog pain scores < 3) within 4 mln. All patients in the 40- and 50-µg groups had excellent analgesia (visual analog pain scores < 1) within 10 min. No patient experienced respiratory depression (respiratory rate < 9 breaths/min), hypoxemia (oxyhemoglobin saturation < 90%), or any hemodynamic alterations (20% change greater or less than baseline heart rate or blood pressure). In the 50-µg group, five of ten patients complained of pruritus.Results indicate that 40 µg intrathecal fentanyl provides satisfactory analgesia for approximately 5 h in an elderly patient population, with a low incidence of side effects.