Credie Renato G, Teixeira Neto Francisco J, Ferreira Tatiana H, Aguiar Antônio J A, Restitutti Fabio C, Corrente José E
Departamento de Cirurgia e Anestesiologia Veterinária, Faculdade de Medicina Veterinária e Zootecnia, Universidade Estadual Paulista, Botucatu, SP, Brazil.
Vet Anaesth Analg. 2010 May;37(3):240-9. doi: 10.1111/j.1467-2995.2010.00528.x. Epub 2010 Mar 10.
To investigate the effects of methadone on the minimum alveolar concentration of isoflurane (ISO(MAC)) in dogs.
Prospective, randomized cross-over experimental study.
Six adult mongrel dogs, four males and two females, weighing 22.8 +/- 6.6 kg.
Animals were anesthetized with isoflurane and mechanically ventilated on three separate days, at least 1 week apart. Core temperature was maintained between 37.5 and 38.5 degrees C during ISO(MAC) determinations. On each study day, ISO(MAC) was determined using electrical stimulation of the antebrachium (50 V, 50 Hz, 10 mseconds) at 2.5 and 5 hours after intravenous injection of physiological saline (control) or one of two doses of methadone (0.5 or 1.0 mg kg(-1)).
Mean (+/-SD) ISO(MAC) in the control treatment was 1.19 +/- 0.15% and 1.18 +/- 0.15% at 2.5 and 5 hours, respectively. The 1.0 mg kg(-1) dose of methadone reduced ISO(MAC) by 48% (2.5 hours) and by 30% (5 hours), whereas the 0.5 mg kg(-1) dose caused smaller reductions in ISO(MAC) (35% and 15% reductions at 2.5 and 5 hours, respectively). Both doses of methadone decreased heart rate (HR), but the 1.0 mg kg(-1) dose was associated with greater negative chronotropic actions (HR 37% lower than control) and mild metabolic acidosis at 2.5 hours. Mean arterial pressure increased in the MET1.0 treatment (13% higher than control) at 2.5 hours.
Methadone reduces ISO(MAC) in a dose-related fashion and this effect is lessened over time. Although the isoflurane sparing effect of the 0.5 mg kg(-1) dose of methadone was smaller in comparison to the 1.0 mg kg(-1) dose, the lower dose is recommended for clinical use because it results in less evidence of cardiovascular impairment.
研究美沙酮对犬异氟烷最低肺泡浓度（ISO(MAC)）的影响。
前瞻性、随机交叉实验研究。
6只成年杂种犬，4只雄性，2只雌性，体重22.8±6.6千克。
动物在3个不同日期用异氟烷麻醉并机械通气，每次间隔至少1周。在测定ISO(MAC)期间，核心体温维持在37.5至38.5摄氏度之间。在每个研究日，在静脉注射生理盐水（对照）或两种剂量美沙酮（0.5或1.0毫克/千克）之一后的2.5小时和5小时，通过电刺激前臂（50伏、50赫兹、10毫秒）测定ISO(MAC)。
对照处理中，2.5小时和5小时时的平均（±标准差）ISO(MAC)分别为1.19±0.15%和1.18±0.15%。1.0毫克/千克剂量的美沙酮使ISO(MAC)在2.5小时时降低48%，在5小时时降低30%，而0.5毫克/千克剂量对ISO(MAC)的降低幅度较小（2.5小时和5小时时分别降低35%和15%）。两种剂量的美沙酮均降低心率（HR），但1.0毫克/千克剂量在2.5小时时具有更强的负性变时作用（HR比对照低37%）并伴有轻度代谢性酸中毒。在2.5小时时，MET1.0处理中的平均动脉压升高（比对照高13%）。
美沙酮以剂量相关方式降低ISO(MAC)，且这种作用随时间减弱。尽管0.5毫克/千克剂量美沙酮的异氟烷节省效应比1.0毫克/千克剂量小，但推荐较低剂量用于临床，因为其导致心血管损害的证据较少。
