Effects of Fentanyl on Sympathetic Activation Associated with the Administration of Desflurane
Authors: Pacentine Gregory G. , Muzi Michael , Ebert Thomas J. 
Published: November 2003

Background
Activation of the sympathetic nervous system occurs when desflurane is inspired shortly after anesthetic induction and when the inspired concentration of desflurane is rapidly increased during steady-state periods of anesthesia. The purpose of this study was to determine the effectiveness and dose response of fentanyl pretreatment in attenuating the neurocirculatory responses to desflurane in healthy human volunteers.

Methods
After Institutional Research Review Board approval, three study groups were selected and, in random order, received either placebo (n = 10), a 2.5-micrograms.kg-1 intravenous bolus of fentanyl citrate followed by a continuous infusion of 1 microgram.kg-1.h-1 (n = 9), or a 5.0-micrograms.kg-1 intravenous bolus followed by an infusion of 2 micrograms.kg-1.h-1 (n = 11) before the administration of desflurane. Arterial (MAP) and central venous (CVP) pressures were measured directly, and heart rate (HR) was determined indirectly. Efferent muscle sympathetic nerve activity (SNA) was recorded from the peroneal nerve by microneurography. After neurocirculatory recordings at conscious unmedicated baseline and 12 min after fentanyl administration, anesthetic induction was carried out with 2.0 mg.kg-1 propofol and 0.2 mg.kg-1 vecuronium. Neurocirculatory measurements were repeated beginning 2 min after induction when desflurane was given via mask (semiclosed circle system, 61/min fresh gas flow, 100% O2) in three incremental 1-min steps (3.6%, 7.2%, and 11%). Intubation occurred 10 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 rapid increase in the inspired gas concentration from 5.4% to 11% ("transition").

Results
Neurocirculatory variables did not differ between the three groups at conscious baseline, after fentanyl, and during steady-state periods of anesthesia. Propofol administration significantly reduced SNA and MAP. The MAP reduction was enhanced in the fentanyl-treated groups. After induction, the increases in SNA and MAP associated with the administration of desflurane by mask were not significantly reduced by fentanyl. The transition from 5.4% to 11% desflurane resulted in increases in SNA, HR, MAP, and fentanyl administration significantly attenuated the HR and MAP components. At the 11% steady-state measurement period, CVP was increased and MAP was decreased from conscious baseline, and these changes were not modified by fentanyl.

Conclusions
The administration of desflurane was associated with increases in SNA, HR, MAP, and CVP. Maximum sympathetic activation and hemodynamic responses occurred 4-5 min after initiating desflurane during induction and 2-3 min after increasing the inspired concentration of desflurane during the "transition" period. Although fentanyl partially attenuated the hemodynamic component in a dose-dependent fashion during the "transition" period, it did not significantly diminish the response during induction.