Use of Intrathecal Fentanyl and Development of Hyperalgesia in Patients Undergoing Elective Cesarean

Opioid analgesic drugs are the main treatment of patients during anesthesia. Although highly effective, their use is not without problems. One is the increasing requirement of these address the same nociceptive stimulus. Opioid induced hyperalgesia could be an explanation studies in animal models. Through mechanisms where N-methyl-D-aspartate receptors, glutamatergic system disturbances and changes in intracellular calcium regulation involved. The hyperalgesia induced by intrathecal opioids is controversial. The investigators propose a model study in patients undergoing cesarean section to study the secondary hyperalgesia induced based on the study of nociceptive thresholds with two methods opioids: Von Frey filaments and digital algometer. If intrathecal fentanyl is used in spinal anesthesia for elective cesarean section, then, an increase in sensitivity will occur. This increase can be measured by von Frey filaments, expressed in increased requirement clinically opioids.