Effects of oxymorphone hydrochloride or hydromorphone hydrochloride on minimal alveolar concentration of desflurane in sheep

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

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.

Determination of minimum alveolar concentration and cardiovascular effects of desflurane in positive-pressure ventilated sheep

OBJECTIVE To determine the minimum alveolar concentration of desflurane (MAC_DES) and effects on cardiovascular variables in positive-pressure ventilated sheep. ANIMALS 13 adult female sheep. PROCEDURES Anesthesia was induced with desflurane. After a 30-minute equilibration at an end-tidal concentration of desflurane (et_DES) of 10.5%, an electrical stimulus (5 Hz/ms and 50 mA) was applied for 1 minute or until gross purposeful movement occurred. The et_DES was then changed by 0.5% (modified up-down method), depending on whether a positive motor response had been elicited, and stimulation was repeated. The MAC_DES was the et_DES midway between a positive and negative response. After MAC_DES was determined, et_DES was increased to 1.3 and 1.6 MAC_DES. Animals were allowed to equilibrate for 15 minutes, and cardiovascular, blood gas, acid-base, and hematologic variables were measured. Times to induction of anesthesia, extubation, attainment of sternal position, and standing and duration of anesthesia were recorded. RESULTS Mean ± SD MAC_DES was 9.81 ± 0.79%. Times to intubation, extubation, and standing were 4.81 ± 2.21 minutes, 14.09 ± 4.05 minutes, and 32.4 ± 12.5 minutes, respectively. Duration of anesthesia was 226 ± 22 minutes. Heart rate increased significantly at induction of anesthesia but otherwise remained at preanesthetic rates. Arterial blood pressures progressively decreased with increasing et_DES; pressures increased slightly only in response to noxious stimulation. CONCLUSIONS AND CLINICAL RELEVANCE The MAC_DES determined here compared favorably with that determined for other sheep populations and indicated similar anesthetic potency as in other species. Desflurane caused dose-dependent arterial hypotension, which indicated the need for careful blood pressure monitoring.