• Mariana do A Correa, Antonio J de A Aguiar, Francisco J Teixeira Neto, Guilherme da M Mendes, Paulo V M Steagall, and Alfredo F da M Lima.
• Department of Veterinary Surgery and Anesthesiology, Faculdade de Medicina Veterinária e Zootecnia, Universidade Estadual Paulista, Botucatu, São Paulo, Brazil, CEP 18618-000.
• Am. J. Vet. Res. 2007 Sep 1;68(9):932-40.

ObjectiveTo evaluate the effects of 2 remifentanil infusion regimens on cardiovascular function and responses to nociceptive stimulation in propofol-anesthetized cats.Animals8 adult cats.ProceduresOn 2 occasions, cats received acepromazine followed by propofol (6 mg/kg then 0.3 mg/kg/min, i.v.) and a constant rate infusion (CRI) of remifentanil (0.2 or 0.3 microg/kg/ min, i.v.) for 90 minutes and underwent mechanical ventilation (phase I). After recording physiologic variables, an electrical stimulus (50 V; 50 Hz; 10 milliseconds) was applied to a forelimb to assess motor responses to nociceptive stimulation. After an interval (> or = 10 days), the same cats were anesthetized via administration of acepromazine and a similar infusion regimen of propofol; the remifentanil infusion rate adjustments that were required to inhibit cardiovascular responses to ovariohysterectomy were recorded (phase II).ResultsIn phase I, heart rate and arterial pressure did not differ between remifentanil-treated groups. From 30 to 90 minutes, cats receiving 0.3 microg of remifentanil/kg/min had no response to noxious stimulation. Purposeful movement was detected more frequently in cats receiving 0.2 microg of remifentanil/kg/min. In phase II, the highest dosage (mean +/- SEM) of remifentanil that prevented cardiovascular responses was 0.23 +/- 0.01 microg/kg/min. For all experiments, mean time from infusion cessation until standing ranged from 115 to 140 minutes.Conclusions And Clinical RelevanceAlthough the lower infusion rate of remifentanil allowed ovariohysterectomy to be performed, a CRI of 0.3 microg/kg/min was necessary to prevent motor response to electrical stimulation in propofol-anesthetized cats. Recovery from anesthesia was prolonged with this technique.

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