Inhaled Anesthetics
What are the most common inhaled anesthetics?
The inhalation anaesthetic agents have changed over the years. The most commonly used agents today are nitrous oxide, isoflurane, sevoflurane and desflurane. In the past, we used halothane and methoxiflurane, but they have historic interest only at this point. This is because, they had side effects and organ toxicity, and have been essentially discontinued. The new inhalation anaesthetics are safer, cleaner, and they have a more rapid onset and a more rapid offset.
What is 'ether'?
Ether was the first volatile anaesthetic that was used as an anaesthetic agent. Ether was discovered in the nineteenth century; I believe the 1840's. It was delivered by dropping it on to a gauze which was inside of a mask over the patient's face. Anyone who has ever had an ether anaesthetic, reports that they've had an obnoxious experience, which includes it to be very unnerving and almost hallucinogenic. As a child, most people who have received ether vortex try not to go to sleep and remember the pungent odour of the gas. It had many side effects and has historic interest only at this time.
What is 'laughing gas'?
Laughing gas is nitrous oxide. Nitrous oxide by itself has some analgesic properties, but it is not effective as a sole anesthetic agent. It is used many times in dentist's offices for its analgesic properties or pain relieving properties. It can cause some nausea, it can cause some giddiness, and it is even being reported to be somewhat of an aphrodisiac. It is now used as a second gas with the other inhalation agents that we discussed - sevoflurane, desflurane and isoflurane. It is used as a second gas because it gets absorbed so quickly, and it thus carries the more potent inhalation agents along with it into the bloodstream of the patients so that the induction of anesthesia is much quicker.
Can general anesthesia be achieved with inhaled anesthesia alone?
General anesthesia can be achieved with inhalational anesthesia alone, but it is not the first choice. The inhalational agents do not have significant pain-relieving properties. If you do a purely inhalation anaesthetic, the patient will wake up in pain and in extremist as if it is a invasive surgical procedure.
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.
What does reversibility mean when used to describe anesthetic gases?
