Aortic surgery: effect of clonidine on intraoperative catecholaminergic and circulatory stability

Abstract

Twenty-eight patients presenting for aortic surgery were randomly assigned in a double-blind, placebo-controlled protocol to receive placebo (n = 14) or clonidine (4.7 +/- 1.2 micrograms.kg-1 po; n = 14), in addition to flunitrazepam 120 min before induction of anesthesia. Plasma catecholamines (CA) and hemodynamic variables were determined at 7 stages during surgery. In the placebo group, plasma epinephrine (E) and norepinephrine (NE) had risen twofold at skin closure compared to baseline (E: from 109 +/- 51 pg.ml-1 to 294 +/- 161 pg.ml-1; NE: from 658 +/- 226 to 1150 +/- 494 pg.ml-1). Plasma CA were significantly lower in the clonidine group (P less than 0.001 and 0.01 vs placebo for NE and E respectively). In both groups, similar directional changes were observed for the circulatory variables, upon aortic clamping and declamping. In the clonidine group, however, mean arterial pressure was lower at most stages (P less than 0.05 vs placebo); moreover, stroke volume index was greater in the clonidine group (P less than 0.05) upon declamping. This improved stability in the clonidine group was achieved with a halving in the number of anesthetic/circulatory interventions (P less than 0.05 vs placebo). Provided intravascular volume is adequate, clonidine suppresses the increase in plasma catecholamines induced by aortic surgery and improves circulatory stability, with a reduced number of anesthetic, circulatory adjustments.

Efeitos do halotano, isoflurano e sevoflurano sobre a função renal em cães sob pinçamento aórtico infra-renal

“…Assim, parece ter ocorrido redistribuição do volume sangüíneo da vasculatura distal para a vasculatura proximal à oclusão aórtica, com aumento da pré-carga. Vários autores observaram aumento das pressões de enchimento durante o pinçamento aórtico [27][28][29] , enquanto outros autores não observaram essas alterações 30 . Por outro lado, muitos autores atribuem, como causa principal do aumento da pressão arterial média durante o pinçamento aórtico, o aumento súbito da impedância do fluxo aórtico, com aumento da pós-carga 31 , acompanhado, muitas vezes, por diminuição do índice cardíaco 27 .…”

“…Na presente pesquisa, o índice de r e s i s t ê n c i a v a s c u l a r s i s t ê m i c a n ã o s e a l t e r o u significantemente em nenhum dos grupos estudados, durante o pinçamento aórtico. Quintin e col. 29 15,9 ± 16,9 14,3 ± 16,6 13,0 ± 13,8 8,4 ± 5,9* DCr (ml.min -1 .kg -1 ) GH 3,6 ± 1,2 4,0 ± 2,7 3,9 ± 2,4 3,9 ± 2,4 4,0 ± 2,0 GI 5,3 ± 4,9 4,4 ± 3,8 4,2 ± 2,7 3,3 ± 1,7 4,6 ± 2,5 GS 4,1 ± 1,6 4,5 ± 2,3 5,5 ± 4,4 5,2 ± 3,5 3,5 ± 2,3 36 . O fator natriuréti-co também pode diminuir a pressão arterial, ao relaxar a musculatura lisa vascular, e a estimulação simpática, e inibir o sistema renina-angiotensina-aldosterona e a liberação de hormônio antidiurético.…”

“…So, it seems to have been blood volume redistribution from distal vessels to vessels proximal to aortic occlusion with increase in preload. Several authors have observed increased filling pressures during aortic cross-clamping [27][28][29] , while others have not observed such changes 30 . On the other hand, several authors consider the sudden aortic flow impedance increase with after load increase, often followed by cardiac index decrease 27 , the major cause for mean blood pressure increase during aortic cross-clamping 31 .…”

“…In our study, systemic vascular resistance index was not significantly changed in all groups during aortic cross-clamping. Quintin et al 29 have observed in men, passive venous retreat distally to aortic cross-clamping with catecholamines (epinephrine and norepinephrine) and angiotensin release, determining vasoconstriction both proximal and distal to cross-clamping with capacitance system decrease and blood flow displacement proximal to cross-clamping, with major interference with venous return, that is, preload, depending on aortic cross-clamping being supra or infra-celiac. In the first situation, venous return has always increased because blood flow displacement was toward muscles proximal to cross-clamping, to lungs and brain.…”

Identification of laryngeal mask airways

“…Thus, clonidine, as well as other alpha,-agonists, has a direct attenuating effect on the sympathetic nervous system. This in turn provides, for example, increased haemodynamic stability during surgery [3,4]. In animal studies clonidine and such novel alpha,-agonists as dexmedetomidine have been shown to possess potent anaesthetic properties.…”