OBJECTIVE: To evaluate effects of various doses of remifentanil on measures of analgesia in anesthetized cats. ANIMALS: 6 healthy adult cats. PROCEDURES: Minimum alveolar concentration (MAC) for isoflurane and thermal threshold responses were evaluated in anesthetized cats. Remifentanil infusions of 0 (baseline), 0.0625, 0.125, 0.25, 0.5, 1, 2, 4, 8, and 16 microg/kg/min were administered; after a 45-minute equilibration period, isoflurane MAC and responses were determined. Isoflurane MAC was determined in anesthetized cats once for each remifentanil infusion rate by use of a standard tail clamp technique. Thermal threshold was measured in awake cats by use of a commercially available analgesiometric probe placed on the lateral portion of the thorax; remifentanil infusions were administered in randomized order to anesthetized cats, and thermal threshold determinations were made by an investigator who was unaware of the infusion rate. RESULTS: Mean +/- SEM median effective concentration (EC(50)) for remifentanil and its active metabolite, GR90291, for the thermal threshold test was 1.00 +/- 0.35 ng/mL and 307 +/- 28 ng/mL of blood, respectively. Dysphoria was detected in all awake cats at the 2 highest remifentanil infusion rates. However, isoflurane MAC during remifentanil infusions was unchanged from baseline values, even at blood opioid concentrations approximately 75 times the analgesic EC(50). CONCLUSIONS AND CLINICAL RELEVANCE: Immobility and analgesia as reflected by thermal threshold testing were independent anesthetic end points in the cats. Results of MAC-sparing evaluations should not be used to infer analgesic potency without prior validation of an MAC-analgesia relationship for specific drugs and species.
OBJECTIVE: To evaluate effects of various doses of remifentanil on measures of analgesia in anesthetized cats. ANIMALS: 6 healthy adult cats. PROCEDURES: Minimum alveolar concentration (MAC) for isoflurane and thermal threshold responses were evaluated in anesthetized cats. Remifentanil infusions of 0 (baseline), 0.0625, 0.125, 0.25, 0.5, 1, 2, 4, 8, and 16 microg/kg/min were administered; after a 45-minute equilibration period, isoflurane MAC and responses were determined. Isoflurane MAC was determined in anesthetized cats once for each remifentanil infusion rate by use of a standard tail clamp technique. Thermal threshold was measured in awake cats by use of a commercially available analgesiometric probe placed on the lateral portion of the thorax; remifentanil infusions were administered in randomized order to anesthetized cats, and thermal threshold determinations were made by an investigator who was unaware of the infusion rate. RESULTS: Mean +/- SEM median effective concentration (EC(50)) for remifentanil and its active metabolite, GR90291, for the thermal threshold test was 1.00 +/- 0.35 ng/mL and 307 +/- 28 ng/mL of blood, respectively. Dysphoria was detected in all awake cats at the 2 highest remifentanil infusion rates. However, isoflurane MAC during remifentanil infusions was unchanged from baseline values, even at blood opioid concentrations approximately 75 times the analgesic EC(50). CONCLUSIONS AND CLINICAL RELEVANCE: Immobility and analgesia as reflected by thermal threshold testing were independent anesthetic end points in the cats. Results of MAC-sparing evaluations should not be used to infer analgesic potency without prior validation of an MAC-analgesia relationship for specific drugs and species.
Authors: Ri Le Ge; Ervin Pejo; Marian Haburcak; S Shaukat Husain; Stuart A Forman; Douglas E Raines Journal: Anesth Analg Date: 2011-11-03 Impact factor: 5.108
Authors: Robert J Brosnan; Bruno H Pypendop; Chalon R Majewski-Tiedeken; Yael Shilo-Benjamini; Jan E Ilkiw Journal: Vet Anaesth Analg Date: 2012-12-24 Impact factor: 1.648
Authors: André Escobar; Rozana Wendler da Rocha; Bruno Henri Pypendop; Darcio Zangirolami Filho; Samuel Santos Sousa; Carlos Augusto Araújo Valadão Journal: PLoS One Date: 2016-03-28 Impact factor: 3.240