Efeitos da dexmedetomidina nas respostas cardiovascular e de oxigenação sistêmica ao pinçamento aórtico infra-renal em cães sob anestesia com sevoflurano

Abstract

A dexmedetomidina (Dex) tem efeito de simpatolise no sistema nervoso central e de inibicao da neurotransmissao nos nervos simpaticos. Assim, a Dex poderia suprimir o estado hiperdinamico do sistema cardiocirculatorio que ocorre durante a cirurgia da aorta. Em modelo de pincamento infra-renal da aorta (Aox) em caes sob anestesia com o sevoflurano, estudaram-se os efeitos cardiovasculares e de oxigenacao sistemica da Dex. Trinta caes foram submetidos a anestesia com sevoflurano, empregando-se 0,75 da concentracao alveolar minima (CAM) do halogenado, ventilados artificialmente e submetidos a Aox e despincamento aortico (DAox). Os animais foram distribuidos aleatoriamente e de modo encoberto em tres grupos: Placebo: (n=10) . infusao de solucao salina; Dex 1 (n=10) . infusao de Dex (1 Êg.kg-1), em 10 minutos, seguida por infusao continua de Dex (1 Êg.kg-1.h-1); e Dex 2 (n=10) - infusao de Dex (2 Êg.kg-1), em 10 minutos, seguida por infusao continua de Dex (2 Êg.kg-1.h-1). Os atributos hemodinamicos e de oxigenacao sistemica foram estudados nos momentos controle, apos a infusao das solucoes, apos 20 e 40 minutos do Aox e apos 20 e 40 minutos do DAox. A Dex diminuiu a frequencia cardiaca (FC) e o indice cardiaco. Na vigencia do Aox, o IC e a FC, nos grupos da Dex, foram menores do que no grupo Placebo (p < 0,05). Em Dex 1 e Dex 2, a pressao arterial media (PAM) apresentou valores mais elevados do que os do Placebo, enquanto a pressao de oclusao da arteria pulmonar (POAP) e o indice de resistencia vascular sistemica (IRVS) aumentaram de maneira INTRODUCAO E LITERATURA 9 dosedependente (p < 0,05). Nos grupos da Dex, o indice de transporte de oxigenio (ITO2) foi menor do que no grupo Placebo, enquanto a saturacao de oxigenio do sangue venoso misto foi menor em Dex 2 em relacao aos demais grupos (p < 0,05).

Dexmedetomidine (Dex) causes a centrally mediated sympatholysis and an inhibition of neurotransmission in sympathetic nerves. Thus, Dex could suppress the circulatory hyperdynamic state which accompanies aortic surgery. We studied the effects of Dex on hemodynamics and systemic oxygenation before, during and after infra-renal aortic cross-clamping (Aox). Thirty dogs were randomly assigned to three different general anesthetic regimens prior to Aox and unclamping (UAox). Group 1 (n=10), control, received 0.75 MAC sevoflurane plus saline infusion. Group 2 (n=10), Dex 1, received 0.75 MAC sevoflurane plus Dex (1 g.kg-1 load) followed by 1 g.kg-1.h-1 infusion. Group 3, Dex 2, received 0.75 MAC sevoflurane plus Dex (2 g.kg-1 load) followed by 2 g.kg-1.h-1 infusion. Hemodynamic and oxygenation variables were measured at baseline, after saline or Dex loading dose, and 20 and 40 min after Aox, and 20 and 40 min after UAox. Cardiac index and heart rate significantly decreased in Dex groups before Aox. Mean arterial pressure after Aox was higher in Dex groups than in Control (P<0.05) while pulmonary artery occlusion pressure and systemic vascular resistance were dose-dependently increased (P<0.05). Systemic oxygen delivery and mixed venous oxygen saturation was lower in Dex 2 compared to control (P<0.05). UAox had little effect on hemodynamics or oxygenation for control and Dex 1, however, Dex 2 was associated with a higher oxygen extraction ratio (P<0.05). In conclusion, Dex deleteriously altered hemodynamic and oxygenation effects of sevoflurane during Aox. INTRODUÇÃO E LITERATURA 11 These effects might limit the use of Dex in association with sevoflurane during aortic surgery.