Balanced anesthesia involves administration of a combination of drugs that provides analgesia, anesthesia, and muscular relaxation. This technique may minimize analgesic requirements and decrease anesthetic-induced adverse effects.1 Studies1,2 have demonstrated the benefits of this technique in dogs and cats.
Opioids are the cornerstone of pain management in small animal practice and are widely used as part of a balanced anesthetic technique. Remifentanil is a short-acting synthetic μ-opioid receptor agonist that has a rapid onset and short duration of action with rapid clearance, which makes it suitable for infusion regimens in cats.3 The drug has been shown to reduce the MAC of isoflurane by approximately 25% in cats; however, this MAC-sparing effect has not been demonstrated in all studies.4,5 In cats, reductions in the MAC of inhalation anesthetics after opioid administration are lower in magnitude than those reported for dogs.4,6 In addition, our experience has been that in cats, infusion of an opioid alone may not always provide consistent and adequate pain management in the perioperative period. This can be particularly true for cats with systemic disease or multiple trauma that have severe pain. In these instances, other analgesic techniques are used to optimize pain relief.7
Ketamine is a dissociative anesthetic and noncompetitive antagonist of the N-methyl-d-aspartate receptor that has been shown to decrease the MAC of isoflurane in cats.8 In addition to its inhalation anesthetic–sparing effects, the drug can be infused as an adjunctive analgesic agent to minimize central sensitization while potentially decreasing opioid requirements.7 Ketamine may also be combined with an opioid infusion to optimize inhalation anesthetic–sparing effects and improve the quality of anesthesia. To the authors’ knowledge, however, the inhalation anesthetic–sparing effects and effects on cardiovascular function of an opioid-ketamine infusion have not been studied in cats.
The purpose of the study reported here was to evaluate the effects of a CRI of remifentanil, alone or in combination with ketamine, on isoflurane requirements, cardiovascular function, and anesthetic recovery in healthy cats undergoing elective ovariohysterectomy. Our hypothesis was that the combination of remifentanil and ketamine would induce significantly greater isoflurane-sparing effects than either remifentanil alone or crystalloid fluids alone.
Constant rate infusion
End-tidal concentration of isoflurane
Minimum alveolar concentration
End-tidal partial pressure of carbon dioxide
Systolic arterial blood pressure
Oxygen saturation as measured by pulse oximetry
Isoflurane USP, Pharmaceutical Partners of Canada, Richmond Hill, ON, Canada.
Tech 4 Anesthesia Vaporiser, Dispomed, Joliette, QC, Canada.
Moduflex Coaxial, Dispomed, Joliette, QC, Canada.
Lifewindow LW6000, Digicare Biomedical Technology, Boynton Beach, Fla.
T/Pump Classic, Matvet Inc, Orchard Park, NY.
Hallowell model 2000, Pittsfield, Mass.
Ultrasonic Doppler Flow Detector, Parks Medical Electronics Inc, Aloha, Ore.
Remifentanil, Novopharm Ltd, Toronto, ON, Canada.
Vetalar, Bioniche Animal Health Canada Inc, Belle Ville, ON, Canada.
Baxter Colleague, Deerfield, Ill.
Graseby syringe pump 3400, Smiths Medical ASD Inc, Saint Paul, Minn.
SPSS Statistics for Windows, version 20.0, IBM Corp, Armonk, NY.
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