Mechanism of Action of Inhaled Anesthetics

Mechanism of Action of Inhaled Anesthetics

The gas has to be inspired and reach the alveoli in the lungs. A significant concentration has to be built up in the lungs and then diffusion occurs from the lungs into the blood stream. The pulmonary capillaries are close beside the alveoli. The air in the alveoli is separated from the blood in the capillaries by two thin layers of cells and a film of interstitial fluid. As the concentration of the inhaled anesthetic builds up in the alveoli the anesthetic diffuses or moves across into the blood stream. It is then carried in the pulmonary vein to the left side of the heart and from there to the arterial circulation.

The drug enters the blood stream and is carried to the brain and the other organs where its effect is experienced. When the agent dissolves in the brain it produces the state of anesthesia. The agent may reduce the ability of the nerves to conduct impulses to each other and activity is reduced, or stopped altogether if you give an overdose. Fortunately, the higher centers controlling consciousness are the first affected and the vital centers such as the respiratory and vasomotor centers are more resistant to this effect. (Figure 1.1)


  • Fresh gas flow (FGF) is determined by the vaporizer and flow meter settings.
  • Inspired gas concentration (Fi) is determined by FGF rate; breathing circuit volume; and circuit absorption.
  • Alveolar gas concentration (FA) is determined by uptake, ventilation, the concentration effect.
  • Arterial gas concentration (Fa) is affected by ventilation/ perfusion mismatching

Figure1.1 Steps of inhaled anesthetics from anesthesia machine to the brain
Modifié le: mercredi 16 novembre 2016, 12:43