The effect of butorphanol with or without subsequent methadone on the fentanyl requirements in dogs undergoing interventional cardiac procedures.

OBJECTIVE

To examine the influence of butorphanol, with or without methadone, on fentanyl requirements in dogs.

STUDY

DESIGN

Retrospective study.

ANIMALS: A group of 23 client-owned dogs presenting for interventional cardiac procedures.

METHODS

All dogs were administered intravenous (IV) butorphanol 0.2-0.3 mg kg-1 for echocardiography 60-90 minutes before anesthesia induction. Thirteen dogs were administered 0.5-1.1 mg kg-1 methadone intramuscularly (IM) (n = 11) or 0.26-0.3 mg kg-1 IV (n = 2) approximately 30 minutes before anesthesia induction. Anesthesia was induced with fentanyl, midazolam, and etomidate, and maintained with fentanyl, lidocaine, and isoflurane. Drug doses and cardiopulmonary data were recorded. Data were analyzed with a Wilcoxon two-sample test or t-test, as appropriate. Categorical data were compared using Fisher's exact test. Values of p < 0.05 were considered significant. Data are presented as mean ± standard deviation or median (range).

RESULTS

There were no significant differences in induction dose of fentanyl [Butorphanol 5 (1-15) μg kg-1; Butorphanol/Methadone 9 (4-12) μg kg-1, p = 0.385] or etomidate [Butorphanol 0.4 (0-0.9) mg kg-1; Butorphanol/Methadone 0.1 (0-1.1) mg kg-1, p = 1.000], maintenance fentanyl dose [Butorphanol 7 (0-30) μg kg-1 hour-1; Butorphanol/Methadone 5 (3-10) μg kg-1 hour-1, p = 0.598] and lidocaine dose [Butorphanol 58.7 (25.3-188.3) μg kg-1 minute-1; Butorphanol/Methadone 50.8 (17.5-112.2) μg kg-1 minute-1, p = 0.403], prevalence of arrhythmias (Butorphanol 9/10, Butorphanol/Methadone 8/13, p = 0.179) or hypotension (Butorphanol 10/10, Butorphanol/Methadone 9/13, p = 0.105) between groups. pH, arterial partial pressures of carbon dioxide and oxygen were not significantly different between groups.

CONCLUSIONS

Butorphanol, with or without methadone, did not influence fentanyl drug doses orcardiopulmonary values in dogs presenting for interventional cardiac procedures.

CLINICAL RELEVANCE: Butorphanol may be considered for IM or IV sedation 60-90 minutes before anesthetic induction with fentanyl.