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

Objective – To determine minimum alveolar concentration of desflurane (MACDES) and its effects on cardiovascular parameters in mechanically ventilated sheep undergoing supramaximum electrical current stimulation. Animals – Thirteen adult female Sardinian breed sheep. Procedures – Anesthesia was induced in sheep with DES in oxygen. After 30 minutes of equilibration at end-tidal desflurane (ETDES) of 10.5 %, an electrical stimulus (5 Hz/1 msec/50 mA) was applied for one minute or until gross purposeful movement occurred. The ETDES was then changed by 0.5% (modified “up-down” method), dependent upon whether a positive motor response had been elicited or not, and stimulation repeated. The MACDES was the ETDES midway between that allowing purposeful movement and that not. Following MACDES determination, ETDES was increased and equilibrated for 15 minutes to values representing 1.3 and 1.6 MACDES. Cardiovascular, blood-gas, acid-base, and blood parameters were recorded, as were times to induction of anesthesia, extubation, sternal, and standing, and anesthesia duration. Results – Mean±SD MACDES was 9.81±0.79%. Times to intubation, extubation, sternal and standing were 4.81±2.21, 14.09±4.05, 19.4±11.8, and 32.4±12.5 min, respectively. Anesthesia time was 226±22 min. Heart rate increased significantly at induction of anesthesia but otherwise stayed at preanesthetic rates. Arterial blood pressures progressively decreased with increasing ETDES, recovering slightly only in moments of noxious stimulation. Blood-gas, acid-base, and other blood parameters remained within acceptable limits. Conclusions and Clinical Relevance – The MACDES determined compares favourably with that found in other sheep populations and indicates similar anesthetic potency as in other species. DES causes dose-dependently arterial hypotension, which requires careful blood pressure monitoring.

OBJECTIVE To determine the minimum alveolar concentration of desflurane (MACDES) 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 (etDES) of 10.5%, an electrical stimulus (5 Hz/ms and 50 mA) was applied for 1 minute or until gross purposeful movement occurred. The etDES 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 MACDES was the etDES midway between a positive and negative response. After MACDES was determined, etDES was increased to 1.3 and 1.6 MACDES. 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 MACDES 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 etDES; pressures increased slightly only in response to noxious stimulation. CONCLUSIONS AND CLINICAL RELEVANCE The MACDES 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.