EFFECTS OF FENTANYL ON SYMPATHETIC ACTIVATION-ASSOCIATED WITH THE ADMINISTRATION OF DESFLURANE

Background: Activation of the sympathetic nervous system occurs when d esflurane is inspired shortly after anesthetic induction and when the inspired concentration of desflurane is rapidly increased during stead y-state periods of anesthesia. The purpose of this study was to determ ine the effectiveness and dose response of fentanyl pretreatment in at tenuating the neurocirculatory responses to desflurane in healthy huma n volunteers. Methods: After Institutional Research Review Board appro val, three study groups were selected and, in random order, received e ither placebo (n = 10), a 2.5-mu g . kg(-1) intravenous bolus of fenta nyl citrate followed by a continuous infusion of 1 mu g . kg(-1) . h(- 1) (n = 9), or a 5.0-mu g . kg(-1) intravenous bolus followed by an in fusion of 2 mu g . kg(-1) . h(-1) (n = 11) before the administration o f desflurane. Arterial (MAP) and central venous (CVP) pressures were m easured directly, and heart rate (HR) was determined indirectly. Effer ent muscle sympathetic nerve activity (SNA) was recorded from the pero neal nerve by microneurography. After neurocirculatory recordings at c onscious unmedicated baseline and 12 min after fentanyl administration , anesthetic induction was carried out with 2.0 mg . kg(-1) propofol a nd 0.2 mg . kg(-1) vecuronium. Neurocirculatory measurements were repe ated beginning 2 min after induction when desflurane was given via mas k (semiclosed circle system, 6 l/min fresh gas flow, 100% O-2) in thre e incremental 1-min steps (3.6%, 7.2%, and 11%). Intubation occurred 1 0 min after propofol administration. Twenty minutes after intubation, recordings were obtained during two steady-state periods during which end-tidal concentrations had achieved 5.4% (0.75 MAC) and 11% (1.5 MAC ) desflurane for at least 10 min. Data also were obtained during the r apid increase in the inspired gas concentration from 5.4% to 11% (''tr ansition''). Results: Neurocirculatory variables did not differ betwee n the three groups at conscious baseline, after fentanyl, and during s teady-state periods of anesthesia, Propofol administration significant ly reduced SNA and MAP. The MAP reduction was enhanced in the fentanyl -treated groups. After induction, the increases in SNA and MAP associa ted with the administration of desflurane by mask were not significant ly reduced by fentanyl. The transition from 5.4% to 11% desflurane res ulted in increases in SNA, HR, MAP, and fentanyl administration signif icantly attenuated the HR and MAP components. At the 11% steady-state measurement period, CVP was increased and MAP was decreased from consc ious baseline, and these changes were not modified by fentanyl. Conclu sions: The administration of desflurane was associated with increases in SNA, HR, MAP, and CVP. Maximum sympathetic activation and hemodynam ic responses occurred 4-5 min after initiating desflurane during induc tion and 2-3 min after increasing the inspired concentration of desflu rane during the ''transition'' period, Although fentanyl partially att enuated the hemodynamic component in a dose-dependent fashion during t he ''transition'' period, it did not significantly diminish the respon se during induction.