How do inhaled anesthetics enter the blood stream?
The way the inhalation agents enter the blood stream is by diffusion. Gases distribute themselves based on pressures between barriers. The anesthetic agent or the inhalational agent begins in a vaporizer and has to get to its site of action, which is the brain. When you turn the vaporizer on, after the anesthesia machine has been hooked up to the patient and the patient is asleep, the gases begin to flow from a high concentration to a low concentration. It flows from the vaporizer through the anesthesia machine, into the anesthesia circuit and then into the pulmonary tree of the patient. At the base of that pulmonary tree are the alvioli, where the gas exchanges and meets the circulatory system, or the blood. As long as the concentration of the anesthetic gas is greater in the lungs than it is in the blood, then it will continue to diffuse into the blood. As it enters the circulation, it then gets distributed all over the body, and specifically, has its mechanism of action in the brain. The gases will continue to move back and forth across all the barriers until equalibrium has been established.
