Intranasal fentanyl appears to be equally effective as IV morphine and superior to intramuscular morphine for the management of acute hospital pain.A fentanyl patient-controlled transdermal system (PCTS) is under development, which aims to allow patients to control administration of fentanyl through the skin to treat postoperative pain. Adverse effects
Fentanyls most common side effects, which affect more than 10% of people, include nausea, vomiting, constipation, dry mouth, somnolence, confusion, and asthenia (weakness). Less frequently, in 3–10% of people, fentanyl can cause abdominal pain, headache, fatigue, anorexia and weight loss, dizziness, nervousness, anxiety, depression, flu-like symptoms, dyspepsia (indigestion), shortness of breath, hypoventilation, apnoea, and urinary retention. Fentanyl use has also been associated with aphasia. Despite being a more potent analgesic, fentanyl tends to induce less nausea, as well as less histamine-mediated itching, than morphine.The duration of action of fentanyl has sometimes been underestimated, leading to harm in a medical context. In 2006, the U.S. Food and Drug Administration (FDA) began investigating several respiratory deaths, but doctors in the United Kingdom were not warned of the risks with fentanyl until September 2008. The FDA reported in April 2012 that twelve young children had died and twelve more made seriously ill from separate accidental exposures to fentanyl skin patches. Respiratory depression
The most dangerous adverse effect of fentanyl is respiratory depression, that is, decreased sensitivity to carbon dioxide leading to reduced rate of breathing, which can cause anoxic brain injury or death. This risk is decreased when the airway is secured with an endotracheal tube (as during anesthesia).
Children younger than three months require medical attention, as might people with serious medical problems such as a compromised immune system or people with other symptoms. Hyperthermia requires treatment.Fever is one of the most common medical signs. It is part of about 30% of healthcare visits by children and occurs in up to 75% of adults who are seriously sick. While fever evolved as a defense mechanism, treating a fever does not appear to improve or worsen outcomes. Fever is often viewed with greater concern by parents and healthcare professionals than is usually deserved, a phenomenon known as fever phobia. Associated symptoms
A fever is usually accompanied by sickness behavior, which consists of lethargy, depression, loss of appetite, sleepiness, hyperalgesia, dehydration, and the inability to concentrate. Sleeping with a fever can often cause intense or confusing nightmares, commonly called "fever dreams". Mild to severe delirium (which can also cause hallucinations) may also present itself during high fevers. Diagnosis
A range for normal temperatures has been found. Central temperatures, such as rectal temperatures, are more accurate than peripheral temperatures. Fever is generally agreed to be present if the elevated temperature is caused by a raised set point and:

Temperature in the anus (rectum/rectal) is at or over 37.5–38.3 °C (99.5–100.9 °F) An ear (tympanic) or forehead (temporal) temperature may also be used.