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The concentration of the anesthetic in blood includes the portion that is undissolved in plasma and the portion that is dissolved (bound to plasma proteins). The more soluble the inhaled anesthetic is in blood compared to in air, the more it binds to plasma proteins in the blood and the higher the blood–gas partition coefficient.
Minimum alveolar concentration or MAC is the concentration, often expressed as a percentage by volume, of a vapour in the alveoli of the lungs that is needed to prevent movement (motor response) in 50% of subjects in response to surgical (pain) stimulus.
An inhalational anesthetic is a chemical compound possessing general anesthetic properties that is delivered via inhalation. They are administered through a face mask, laryngeal mask airway or tracheal tube connected to an anesthetic vaporiser and an anesthetic delivery system .
Inhaled anesthetics are eliminated via expiration, following diffusion into the lungs. This process is dependent largely upon the anesthetic blood:gas partition coefficient, tissue solubility, blood flow to the lungs, and patient respiratory rate and inspiratory volume. [4]
Sevoflurane is an inhaled anesthetic that is often used to induce and maintain anesthesia in children for surgery. [17] During the process of awakening from the medication, it has been associated with a high incidence (>30%) of agitation and delirium in preschool children undergoing minor noninvasive surgery. [ 17 ]
It is a potent anesthetic with a minimum alveolar concentration (MAC) of 0.74%. [14] Its blood/gas partition coefficient of 2.4 makes it an agent with moderate induction and recovery time. [15] It is not a good analgesic and its muscle relaxation effect is moderate. [16] Halothane is colour-coded red on anaesthetic vaporisers. [17]
The more lipophillic the anesthetic agent is, the more potent the anesthetic agent is. [3] [8] [18] This principle became known as the Meyer-Overton Correlation. It originally compared the anesthetic partition coefficient in olive oil (X-axis) to the effective dose that induced anesthesia in 50% (i.e., EC50) of the tadpole research subjects (Y ...
The Meyer-Overton correlation for anaesthetics. A nonspecific mechanism of general anaesthetic action was first proposed by Emil Harless and Ernst von Bibra in 1847. [9] They suggested that general anaesthetics may act by dissolving in the fatty fraction of brain cells and removing fatty constituents from them, thus changing activity of brain cells and inducing anaesthesia.