title: Sympathetic and vascular consequences from remifentanil in humans.
abstract: We explored the possible mechanisms of hypotension during the administration of sedation-analgesia doses of remifentanil in young (ASA physical status I) volunteers (n = 24). Cardiorespiratory and sympathetic variables were collected at baseline and at plasma concentrations of remifentanil (2 and 4 ng/mL). Monitoring included electrocardiogram, heart rate (HR), direct blood pressure, muscle sympathetic nerve activity, and forearm blood flow (FBF). A cold pressor test (1-min hand immersion in ice water) quantified analgesia effectiveness (visual analog scale, 0-100). Visual analog scale to the cold pressor test (62 at baseline) decreased to 27 and 18 during remifentanil infusions. Respiratory rate decreased and end-tidal carbon dioxide (ETCO(2)) increased with increasing doses of remifentanil; HR, direct blood pressure, muscle sympathetic nerve activity, SpO(2) remained unchanged, but FBF increased compared with placebo. In a second study (n = 7), timed respiration was used to maintain ETCO(2) during remifentanil, but FBF still increased. In a third study (n = 11), direct effects of remifentanil on vascular tone were determined with progressive infusions from 1 to 100 micro g/h into the brachial artery; FBF increased significantly from 3.5 to 4.3 mL/min per 100 mL of tissue (approximately 13%-18% increase). Sedative doses of remifentanil resulted in analgesia but no changes in neurocirculatory end-points except FBF. Direct effects of remifentanil on regional vascular tone may play a role in promoting hypotension.
  
  
  CONCLUSIONS
  Remifentanil occasionally has been associated with hypotension, the mechanism of which is unclear. This study found that remifentanil directly causes the forearm arterial vasculature to dilate.
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin and Veterans Affairs Medical Center, Milwaukee.
authors.forename: Randa K
authors.initials: RK
authors.lastname: Noseir
authors.forename: David J
authors.initials: DJ
authors.lastname: Ficke
authors.forename: Anjana
authors.initials: A
authors.lastname: Kundu
authors.forename: Shahbaz R
authors.initials: SR
authors.lastname: Arain
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Ebert
mesh_terms: D000328:Adult; D000701:Analgesics, Opioid / Q000009:adverse effects* / Q000627:therapeutic use; D018686:Anesthetics, Intravenous / Q000009:adverse effects* / Q000627:therapeutic use; D001794:Blood Pressure / Q000187:drug effects; D005260:Female; D005542:Forearm / Q000098:blood supply; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation; D010147:Pain Measurement; D010880:Piperidines / Q000009:adverse effects* / Q000627:therapeutic use; D012039:Regional Blood Flow / Q000187:drug effects; D000077208:Remifentanil; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000187:drug effects*
chemical_list: D000701:Analgesics, Opioid; D018686:Anesthetics, Intravenous; D010880:Piperidines; D000077208:Remifentanil