Effect of remifentanil hydrochloride administered via constant rate infusion on the minimum alveolar concentration of isoflurane in cats.
OBJECTIVE
To evaluate the effects of increasing doses of remifentanil hydrochloride administered via constant rate infusion (CRI) on the minimum alveolar concentration (MAC) of isoflurane in cats.


METHODS
6 healthy adult cats.


METHODS
For each cat, 2 experiments were performed (2-week interval). On each study day, anesthesia was induced and maintained with isoflurane; a catheter was placed in a cephalic vein for the administration of lactated Ringer's solution or remifentanil CRIs, and a catheter was placed in the jugular vein for collection of blood samples for blood gas analyses. On the first study day, individual basal MAC (MAC(Basal)) was determined for each cat. On the second study day, 3 remifentanil CRIs (0.25, 0.5, and 1.0 microg/kg/min) were administered (in ascending order); for each infusion, at least 30 minutes elapsed before determination of MAC (designated as MAC(R0.25), MAC(R0.5), and MAC(R1.0), respectively). A 15-minute washout period was allowed between CRIs. A control MAC (MAC(Control)) was determined after the last remifentanil infusion.


RESULTS
Mean +/- SD MAC(Basal) and MAC(Control) values at sea level did not differ significantly (1.66 +/- 0.08% and 1.52 +/- 0.21%, respectively). The MAC values determined for each remifentanil CRI did not differ significantly. However, MAC(R0.25), MAC(R0.5), and MAC(R1.0) were significantly decreased, compared with MAC(Basal), by 23.4 +/- 7.9%, 29.8 +/- 8.3%, and 26.0 +/- 9.4%, respectively.


CONCLUSIONS
The 3 doses of remifentanil administered via CRI resulted in a similar degree of isoflurane MAC reduction in adult cats, indicating that a ceiling effect was achieved following administration of the lowest dose.
Ferreira
Tatiana H
TH
Department of Veterinary Surgery and Anesthesiology, School of Veterinary Medicine and Animal Science, University of São Paulo State, Botucatu, SP, Brazil, 18618-000.
Aguiar
Antonio J A
AJ
Valverde
Alexander
A
Neto
Francisco J Teixeira
FJ
Steagall
Paulo V M
PV
Soares
João H N
JH
D018686:Anesthetics, Intravenous / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis; D002415:Cats / Q000378:metabolism*; D005260:Female; D007262:Infusions, Intravenous; D007530:Isoflurane / Q000378:metabolism*; D008297:Male; D010880:Piperidines / Q000008:administration & dosage / Q000494:pharmacology*; D011650:Pulmonary Alveoli / Q000187:drug effects* / Q000378:metabolism*; D000077208:Remifentanil
D018686:Anesthetics, Intravenous; D010880:Piperidines; D007530:Isoflurane; D000077208:Remifentanil