BACKGROUND AND OBJECTIVES: Clinical and experimental studies have been developed to identify inhalational anesthetics action sites to determine clinically observed functional changes produced on central nervous system structures responsible for the anesthetic status. This study aimed at reviewing results obtained by several authors in recent clinical and experimental studies in an attempt to explain action mechanisms of inhalational anesthetics on the central nervous system. CONTENTS: To help understanding the complex action mechanisms of inhalational anesthetics on the central nervous system, these were divided in three levels: macroscopic, microscopic, and molecular. A group of authors have recently divided those action mechanisms in: organic, cellular, and entropy inhibitors. These mechanisms would try to explain the anesthetic status able to provide patients with two major reactions: 1) immobility in response to noxious stimuli and 2) amnesia. Other desirable effects, such as analgesia and hypnosis are also obtained by inhalational anesthesia, however such effects per se or in combination, do not define the anesthetic status. Based on those concepts, this group classifies inhalational anesthetics as: 1) complete anesthetics, or providing immobility and amnesia; and 2) incomplete anesthetics, or not providing immobility, but providing amnesia. CONCLUSIONS: According to several recent studies, it is possible that amnesia and unconsciousness are a consequence of the anesthetic action predominantly on the brain, while immobility, that is, inhibition of motor response to noxious stimuli, would be a consequence of the preferential and initial anesthetic action on the spinal cord. These actions occur by energy transformation inhibition (entropy) generating action potentials in nervous cells (fibers), particularly the synapses.
ANESTHETICS, Inhalational
