Efeitos da administração epidural de dexmedetomidina sobre a concentração alveolar mínima do isofluorano em cães

Abstract

A administracao intravenosa de dexmedetomidina reduz significativamente a concentracao alveolar minima (CAM) dos agentes halogenados. No entanto, esse beneficio e frequentemente acompanhado por efeitos colaterais tipicos dos agonistas 2, como hipertensao, bradicardia e reducao do debito cardiaco. Ha indicios de que a administracao epidural de doses reduzidas de dexmedetomidina pode potencializar e prolongar seu efeito analgesico. Hipotetizou-se que a administracao epidural de dexmedetomidina reduziria a CAM do isofluorano de forma dose e tempo-dependente, sem ocasionar depressao cardiovascular significativa. Objetivou-se tambem caracterizar as alteracoes do indice bispectral (BIS) induzidas pela estimulacao nociceptiva empregada na mensuracao da CAM, bem como o efeito da dexmedetomidina epidural sobre essas alteracoes. Seis caes higidos (18,8}4,0 kg) foram anestesiados com isofluorano em 4 ocasioes distintas, com intervalo de 7 dias. Em cada anestesia, os animais receberam aleatoriamente 1 de 4 tratamentos pela via epidural. No tratamento controle, administrou-se solucao salina, enquanto nos tratamentos DEX1.5, DEX3 e DEX6, administrou-se dexmedetomidina nas doses de 1,5 . 3,0 e 6,0 Êg/kg, respectivamente. A CAM do isofluorano foi mensurada as 2 e 4,5 horas apos os tratamentos epidurais, por meio de estimulacao nociceptiva supramaxima (50V, 50 Hz e 10 ms) no membro pelvico. O valor medio de CAM (} desvio padrao) no tratamento controle foi de 1,57}0,23% e 1,55}0,25% as 2 e 4,5 horas, respectivamente. Quando comparado ao tratamento controle, o valor de CAM observado no tratamento DEX1,5 foi reduzido em 13% as 2 horas (1,35}0,11%), enquanto que a reducao as 4,5 horas (7% de reducao, CAM: 1,43}0,23%) nao foi significativa. No tratamento DEX3, a CAM foi significativamente reduzida em 29% (1,12}0,18%) e 13% (1,33}0,16%) as 2 e 4,5 horas, respectivamente. Reducoes de maior magnitude foram observadas...

Intravenous administration of dexmedetomidine significantly reduces the minimum alveolar concentration (MAC) of inhalant anesthetics. However, this beneficial effect is often associated with side effects such as hypertension, bradycardia, and a decrease in cardiac output. There are evidences epidural administration of relatively low doses of dexmedetomidine may result in more prolonged analgesia than intravenous administration of higher doses. The hypothesis of the present study is that epidural administration of dexmedetomidine would reduce isoflurane MAC in a dose and time-related fashion, without causing marked cardiovascular changes. This study aimed also to characterize the changes in bispectral index (BIS) induced by nociceptive stimulation used for MAC determinations and the effects of epidural dexmedetomidine on these changes. Six healthy dogs (18.8 8l4,0 kg) were anesthetized with isoflurane at 4 different occasions with at least 1-week intervals. On each anesthetic procedure, animals received 1 of 4 epidural treatments. Physiologic saline solution was administered in the control treatment, while for the treatments DEX1.5, DEX3, and DEX6, dexmedetomidine was administered at the doses of 1.5, 3.0, and 6.0 ìg/kg, respectively. Isoflurane MAC was assessed at 2 and 4.5 hours after epidural injections by means of supramaximal nociceptive stimulation (50V, 50 Hz e 10 ms) administered to the pelvic limb. Mean (l SD) isoflurane MAC in the control treatment was 1.57l0.23% and 1.55l0.25% at 2 e 4,5 hours, respectively. When compared to controls, mean MAC values observed in the DEX1.5 treatment were significantly reduced by 13% at 2 hours (1.35l0.11%), while the reduction observed at 4.5 hours (7% reduction, MAC: 1.43l0.23%) was not statistically significant... (Complete abstract click electronic access below)