Brazilian Journal of Anesthesiology
https://bjan-sba.org/article/doi/10.1590/S0034-70942005000100013
Brazilian Journal of Anesthesiology
Review Article

Imobilidade: uma ação essencial dos anestésicos inalatórios

Immobility: essential inhalational anesthetics action

Leonardo Teixeira Domingues Duarte; Renato Ângelo Saraiva

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Resumo

JUSTIFICATIVA E OBJETIVOS: A imobilidade é uma característica essencial da anestesia geral e que deve ser buscada e mantida durante todo o ato anestésico. A potência anestésica, chamada Concentração Alveolar Mínima (CAM), é a expressão da inibição dos movimentos em resposta a estímulos nociceptivos. Entretanto, apesar da medula espinhal ser reconhecida como principal mediadora da imobilidade cirúrgica, os mecanismos celulares e subcelulares da ação dos anestésicos inalatórios para produzirem imobilidade não são, ainda, totalmente conhecidos. Tendo em vista o grande avanço na pesquisa dos mecanismos de ação dos anestésicos inalatórios e a resultante grande quantidade de informações, essa revisão tem como objetivo avaliar criticamente os estudos clínicos e experimentais realizados para identificação dos mecanismos e locais de ação dos anestésicos inalatórios para produção de imobilidade em resposta a estímulos nociceptivos. CONTEÚDO: Os mecanismos de ação dos anestésicos inalatórios no SNC podem ser divididos em três níveis: macroscópico, microscópico e molecular. No aspecto macroscópico, estudos comportamentais mostraram ser a medula espinhal o principal local da ação anestésica para promover imobilidade em resposta à estimulação dolorosa. No nível celular, a excitabilidade dos motoneurônios, neurônios nociceptivos e a transmissão sináptica estão, todos, envolvidos na ação dos anestésicos inalatórios. Sob o ponto de vista molecular, diversos receptores são afetados pelos anestésicos, mas poucos devem mediar diretamente a ação anestésica. Entre estes, destacam-se os receptores de glicina, NMDA de glutamato, 5-HT2A, e canais de sódio voltagem-dependentes. CONCLUSÕES: A imobilidade produzida pelos anestésicos inalatórios é mediada, principalmente, através de uma ação sobre a medula espinhal. Esse efeito ocorre pela ação anestésica sobre a excitabilidade dos neurônios motores espinhais, mas também sobre neurônios e interneurônios nociceptivos do corno posterior da medula. A ação sobre os receptores específicos exerce efeito sobre a transmissão sináptica desses neurônios.

Palavras-chave

ANESTESIA, Geral, MONITORIZAÇÃO

Abstract

BACKGROUND AND OBJECTIVES: Immobility is an essential component of general anesthesia and should be looked for and maintained throughout anesthesia. Anesthetic potency, called Minimum Alveolar Concentration (MAC), results from the inhibition of movement response to noxious stimulation. However, although spinal cord is recognized as the primary mediator of surgical immobility, cellular and subcelular mechanisms of action of inhaled anesthetics to produce immobility are not yet totally known. Considering major research advances on mechanisms of action of inhaled anesthetics and resulting wide variety of information, this review aimed at critically evaluating clinical and experimental studies performed to identify sites of action and mechanisms of inhaled anesthetics to promote immobility in response to noxious stimulations. CONTENTS: Complex mechanisms of action of inhaled anesthetics on central nervous system may be divided into three levels: macroscopic, microscopic, and molecular. Macroscopically, behavioral studies have shown spinal cord to be the primary anesthetic site of action to promote immobility in response to noxious stimulations. At cellular level, excitability of motor neurons, nociceptive neurons and synaptic transmission are involved in the anesthetic action. At molecular level, several receptors are affected by inhaled anesthetics, but only a few may directly mediate anesthetic action, among them: glycine, glutamate AMPA and 5-HT2A receptors, in addition to voltage-gated sodium channels. CONCLUSIONS: Inhaled anesthetics-induced immobility is primarily mediated by an action on the spinal cord, as a consequence of anesthetic action upon motor neurons excitability and upon nociceptive neurons of the spinal cord dorsal horn. Actions on specific receptors have an effect on their synaptic transmission.

Keywords

ANESTHESIA, General, MONITORING

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