title: Central analgesic mechanisms: a review of opioid receptor physiopharmacology and related antinociceptive systems.
abstract: Clinical applications of these principles, based on the increased understanding of central analgetic mechanisms, are already being undertaken. Not only does the use of intrathecal and epidural opioids have the potential to decrease pain and related morbidity after surgical procedures, but there is at least one study that demonstrates a significant reduction in both major morbidity and mortality in high-risk surgical patients in whom epidural anesthesia and analgesia were used. These principles are also useful for the management of patients undergoing cardiac surgery. Currently, high-dose narcotic anesthesia is the technique of choice for such patients because of the greater hemodynamic stability this anesthetic technique provides. However, breakthrough hypertension and tachycardia still occur, and prolonged postoperative ventilation is a necessary consequence due to the high doses of narcotics that are required. In one study of patients undergoing coronary artery surgery, preoperative administration of clonidine, 5 micrograms/kg, orally, was demonstrated to decrease fentanyl requirements by 45% (110 to 61 micrograms/kg) while producing a similar degree of hemodynamic stability as seen with high-dose fentanyl. Extubation times were not compared, but the significantly lower dosage of fentanyl in the clonidine-treated group would be expected to lead to an earlier extubation. Whether similar potentiation of narcotic effects would be seen with dexmedetomidine, which may also prevent narcotic-induced rigidity, has not been determined, but the clinical application of such synergistic and complementary agents is another consequence of the greater understanding of central analgesic mechanisms, and augurs well for the future.
authors.affiliation: Department of Anaesthesia, University Hospital, University of Western Ontario, London, Canada.
authors.forename: J M
authors.initials: JM
authors.lastname: Murkin
mesh_terms: D004723:Endorphins / Q000494:pharmacology / Q000502:physiology; D006801:Humans; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D011957:Receptors, Opioid / Q000502:physiology*
chemical_list: D004723:Endorphins; D011942:Receptors, Adrenergic, alpha; D011957:Receptors, Opioid