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The aim of this study was to assess the effect of duration of anaesthesia and concentration of isoflurane on global perfusion as well as intestinal microperfusion and oxygenation. Nine Warmblood horses were premedicated with xylazine; anaesthesia was induced with midazolam and ketamine, and maintained with isoflurane. Horses were ventilated to normocapnia. During 7 h of anaesthesia, mean arterial blood pressures (MAP), heart rate, central venous pressure, pulmonary artery pressure, expiratory isoflurane concentration (E T Iso) and cardiac output using lithium dilution were measured; cardiac index (CI) was calculated. Intestinal microperfusion and oxygenation were measured using laser Doppler flowmetry and white-light spectrophotometry. Surface probes were placed via median laparotomy on the serosal and mucosal site of the jejunum and the pelvic flexion of the colon. After 3 h of constant E T Iso (1.4%), E T Iso was increased in 0.2% increments up to 2.4%, followed by a decrease to 1.2% and an increase to 1.4%. The CI and MAP decreased continuously with increasing E T Iso to 40 ± 5 mL/kg/min and 52 ± 8 mmHg, respectively. Microperfusion and oxygenation remained unchanged until an E T Iso of 2.0% resulted in CI and MAP of 48 ± 5 mL/kg/min and 62 ± 6 mmHg, respectively, and then decreased rapidly. When E T Iso decreased back to baseline, CI, MAP, microperfusion and oxygenation recovered to baseline. Isoflurane concentration but not duration of isoflurane anaesthesia influenced central and intestinal oxygenation and perfusion in healthy horses. Under isoflurane, intestinal perfusion appeared to be preserved until a threshold MAP or blood flow was reached. [ABSTRACT FROM AUTHOR]

• Fentanyl analgesic efficacy and duration and minimum anti-nociceptive plasma concentrations in horses were investigated. • Fentanyl administered at 10 μg/kg IV produced significant antinociception for 10–30 min in horses. • Dose-dependent increased locomotor activity was the main side effect. • Fentanyl plasma concentrations of ≥6.1–6.8 ng/mL appeared necessary to induce detectable anti-nociception in horses. There are few investigations relating anti-nociception to plasma concentrations of fentanyl in horses. The study objective was to evaluate analgesic efficacy and duration in horses and determine the minimum anti-nociceptive plasma concentrations. Eight horses were treated with saline (P) and fentanyl (F 2.5 = 2.5 μg/kg; F 5 = 5 μg/kg; F 10 = 10 μg/kg) given IV over 5 min, with a wash-out period of 10 days. To evaluate thermal (°C) and mechanical (N) nociceptive threshold single stimulations were applied prior to (baseline) and 10, 30, 60, 90, 120, 180, 240, 300, 360, 420, 540 min and 22.5 h after treatment. Plasma fentanyl concentrations were measured at specific time points. Locomotor activity, heart rate, respiratory rate and gastrointestinal sounds were recorded. Two-way repeated measures ANOVA and pairwise comparisons were used for data analysis (P < 0.05). With treatment F 10 , there was a significant increase in thermal threshold above baseline (47.2 ö 4.1 °C) at t 10 (53.7 ö 4.2 °C) and t 30 (52.1 ö 5.6 °C), whereas mechanical threshold increased considerably above baseline (3.7 ö 1.3 N) only at t 10 (6.6 ö 3.6 N). Estimated mean minimum anti-nociceptive plasma concentration determined by thermal stimulation was 6.1–6.8 ng/mL. Dose-dependent increased locomotion occurred, but no significant changes in heart rate, respiratory rate and gastrointestinal sounds were observed. Fentanyl IV at 10 μg/kg produced anti-nociception for 10–30 min and fentanyl plasma concentrations of ≥6.1–6.8 ng/mL appear necessary to induce thermal anti-nociception. Dose-dependent increased locomotion was the main side effect observed. [ABSTRACT FROM AUTHOR]