Inhaled anesthetics like isoflurane, sevoflurane, and desflurane are administered via a vaporizer that converts the liquid anesthetic into gas, which the patient inhales through the anesthesia circuit. These gasses are absorbed into the bloodstream through the lungs' alveoli. The speed of absorption depends on several factors, including the solubility of the anesthetic in blood, the concentration of the anesthetic in the inhaled gas mixture, the rate of ventilation, and the partial pressure of the anesthetic in the alveoli.
The solubility of an anesthetic in blood is a key factor in determining how quickly it takes effect and how fast patients recover. Agents with low blood-gas solubility, like desflurane, equilibrate quickly between the alveoli and the blood, leading to faster induction and recovery. In contrast, agents with higher solubility, like isoflurane, have a slower onset and recovery. The concentration of the anesthetic in the gas mixture also influences how quickly it is absorbed, with higher concentrations speeding up absorption.
Once in the bloodstream, inhaled anesthetics are distributed throughout the body, including the brain, where they exert their primary effects. Distribution is influenced by tissue perfusion, the solubility of the anesthetic in different tissues, and cardiac output. Organs with high blood flow, such as the brain, heart, liver, and kidneys, absorb the anesthetic more quickly than less perfused tissues like muscle and fat. The rapid equilibration of anesthetics in the brain is particularly important for the onset of anesthesia, while redistribution to less perfused tissues leads to recovery as the anesthetic concentration in the brain decreases.
