MAC-Sparing Effect of Transdermal Fentanyl in Sevoflurane-Anesthetized Sheep

Abstract Transdermal fentanyl allows for consistent plasma concentrations of a potent synthetic μ-opioid receptor agonist and can provide constant post-operative analgesia for up to 72 h. The aim of this study was to determine the reduction of the minimum alveolar concentration of sevoflurane (MACSEVO) by transdermal fentanyl in nonpregnant ewes. Nine sheep were mask induced with sevoflurane (SEVO in oxygen). MACSEVO determinations involved electrical current applied to the lateral metacarpus as a supramaximal stimulus and measurements in duplicate. Seven days later, a fentanyl patch (75 μg/h) was applied to each sheep and 15.1 ± 1.8 h later the MAC re-determined (MACSF). MACSF was 1.99 ± 0.32 %, corresponding to 25.6 ± 8.1 % reduction from MACSEVO (P < 0.001). Transdermal fentanyl produces a significant MACSEVO-sparing effect with minimal effect on cardiovascular parameters

MAC Sevo N2O Data Plos One.xlsx

Animals were initially anesthetized with SEVO in oxygen (O₂) and exposed to an electrical current as supramaximal noxious stimulus in order to determine MAC_SEVO (in duplicates). Thereafter, 70% N₂O was added to the inspired gas and the MAC re-determined in the presence of N₂O (MAC_SN). A subgroup of sheep were anesthetized a second time with SEVO/N₂O for re-determination of MAC_SN, after which atipamezole (0.2 mg/kg, IV) was administered for MAC_SNA determinations. Sheep were anesthetized a third time, initially with only SEVO/O₂ to re-determine MAC_SEVO, after which atipamezole (0.2 mg/kg, IV) was administered for determination of MAC_SA

First and second determinations of MAC_SEVO, MAC_SN, MAC_SNA, MAC_SA, and MAC_SEVO in the form of pooled data.

<p>First and second determinations of MAC_SEVO, MAC_SN, MAC_SNA, MAC_SA, and MAC_SEVO in the form of pooled data.</p

End-tidal concentrations of SEVO and CO₂ and physiological variables recorded during MAC determinations.

<p>End-tidal concentrations of SEVO and CO₂ and physiological variables recorded during MAC determinations.</p