In a double blinded randomized clinical trial, 154 patients scheduled for lower abdominal surgery (after receiving sufentanil 0.2 mcg/kg, propofol 2.5 mg/kg and atracurium 0.5 mg/kg) are anesthetized and intubated. Patients are in the age of 18-65, ASA I and II, are not pregnant and without prior history of cardiopulmonary and nervous system diseases, with no history of opioids, tranquilizers and theophyline use. Infusion of propofol 200 mcg/kg will be continued. Patients with hypotension which cause decreasing propofol dose or use of vasoactive agents or who needed more opioids during surgery, are excluded. At the end of surgery, infusion of propofol will be hold on after the beginning of spontaneous breathing and in one group aminophyline 1 mg/kg in 10 ml volume with distilled water will be injected intravenously during 2 minutes and in the other group only 10 ml distilled water will be injected. Heart rate, mean arterial blood pressure and oxygen saturation will be recorded every 2 minutes until extubation and then every 5 minutes till release from recovery ( by getting at least 8 points from Alderet score). Any other side effects (nausea, vomiting, hypotension, desaturation,...) will be recorded.