Determination of the sevoflurane sparing effect of methadone in cats

Authors

  • Tatiana H. Ferreira,

    1. Department of Anesthesiology, Botucatu Medical School, São Paulo State University – UNESP, Botucatu, SP, Brazil
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  • Eugene P Steffey,

    1. Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA
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  • Khursheed R. Mama,

    1. Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA
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  • Marlis L Rezende,

    1. Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA
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  • Antonio JA Aguiar

    1. Department of Veterinary Surgery and Anesthesiology, School of Veterinary Medicine and Animal Science, São Paulo State University – UNESP, Botucatu, SP, Brazil
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Khursheed R. Mama, Department of Clinical Sciences, Colorado State University, Fort Collins, CO 80523, USA. E-mail: kmama@colostate.edu

Abstract

Objective  To determine the magnitude and duration of sevoflurane minimum alveolar concentration (MAC) reduction following a single intravenous (IV) dose of methadone in cats.

Study design  Prospective experimental study.

Animals  Eight (four females and four males) healthy mixed-breed adult (1–2 years) cats weighing 5.82 ± 0.42 kg.

Methods  Anesthesia was induced and maintained with sevoflurane. Intravenous catheters facilitated administration of methadone and lactated Ringer’s solution. After baseline MAC determination in triplicate using a tail clamp technique, 0.3 mg kg−1 of methadone was administered IV. End-tidal sevoflurane concentration (e′SEVO) was reduced and MAC was redetermined. In an effort to determine the duration of MAC reduction, measurements were repeated in a stepwise manner until MAC values returned to baseline. After the last stimulation, the e′SEVO was increased to 1.2 individual MAC for 15 minutes, then sevoflurane was discontinued and cats were allowed to recover from anesthesia.

Results  Baseline sevoflurane MAC was 3.18 ± 0.06%. When compared with baseline the sevoflurane MAC after methadone administration was significantly reduced by 25, 15 and 7% at 26, 76 and 122 minutes, respectively. The final MAC value (3.09 ± 0.07%) determined 156 minutes after methadone administration was not significantly different from baseline.

Conclusions and clinical relevance  Intravenous methadone (0.3 mg kg−1) significantly decreased MAC of sevoflurane in cats but the effect was short-lived.

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