• Any adverse events will be recorded. Oxygen saturation will be monitored continuously. Vital signs (BP, HR, RR, T), oxygen saturation, and concomitant medications will be recorded at Hours 0, 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and every 4 hours thereafter. [ Time Frame: Safety outcomes will be collected at intervals throughout the drug system application for a maximum of 72 hours. ] [ Designated as safety issue: Yes ]
  

• Patient Global Assessment, Investigator Global Assessment and Parent Assessment of Patient Use will be completed every 24 hours. Serum fentanyl concentration will be collected at Hours 3, 6,12, and 24. [ Time Frame: Patient, Investigator and Parent Assessments of the treatment will be completed every 24 hours for a maximum of 72 hours. Pharmacokinetic measurements will be completed 4 times during every 24 hours of treatment for a maximum of 12 times over 72 hours. ] [ Designated as safety issue: No ]
  

This will be a multicenter, open-label study in which hospitalized pediatric post-operative patients will receive the fentanyl HCl 40 mcg system for up to 3 consecutive days. After their surgery, patients will be brought to the recovery room for initial observation following general or regional anesthesia for abdominal, pelvic/genitourinary, orthopedic, or thoracic surgery. Post surgery procedures will be preformed and when analgesia is required, the patient will be titrated to analgesic comfort (a pain score < 4 on a scale 0-10) for at least 30 minutes with an intravenous opioid as clinically appropriate. After a patient has been comfortable (pain intensity of < 4 on 0 -10 color visual analog scale ) for > 30 minutes and has been monitored during recovery and is awake, able to answer questions and follow commands he/she will be assessed for pain intensity, vital signs, and oxygen saturation (amount of oxygen in the blood). If the patient meets study entry criteria, baseline assessments (pain intensity, vital signs, and oxygen saturation) will be completed and the fentanyl HCl 40 mcg system will be applied. During the first 3-hours of the treatment, if a patient successfully completed an on-demand dose and pain relief was still inadequate, the patient could deliver another dose of fentanyl, or be re-titrated to comfort with single or multiple intravenous doses of supplemental opioid medication (IV fentanyl or IV morphine) per study physician's clinical discretion. Supplemental IV doses of opioid medications can be administered in the first 3-hours of system application, but are prohibited after Hour 3. If pain control is judged inadequate with the combined use of fentanyl HCl 40 mcg system and the use of supplemental analgesia, the patient may be withdrawn from the study. Patients will receive fentanyl HCl 40 mcg system. Fentanyl will be delivered upon patient activation over 10 minutes for a maximum of 6 doses/hour for up to 24 hrs or 80 total doses whichever occurs first for up to three consecutive days.