Laughing Gas -- Nitrous Oxide -- for General Anesthesia
What is Laughing Gas? What is Nitrous Oxide?
Laughing gas, scientifically known as nitrous oxide, is inhaled for use as a analgesic (pain reliever), partial anesthetic (for lack of a better phrase), and sedative agent.
Nitrous oxide, N2O, exists as an inert gas at room temperature. It is considered non-toxic and non-flammable, but combustible. As an odorless, colorless gas it is found both in soil and in the ocean as a by-product of natural chemical reactions.
Nitrous oxide is used in both rockets and race cars to improve the efficiency of oxygen combustion and increase power to the engines.
The recreational abuse of inhalants from aerosol cans ("whippets") is due to the presence of nitrous oxide. The euphoria, relaxation and dissociation produced is very short-lived after a one-time inhalation.
As an anesthetic, nitrous oxide is the oldest gas still in use.
History of Nitrous Oxide Use for Anesthesia
The use of nitrous oxide for sedation, pain relief and "partial" anesthesia goes back hundreds of years. The first mention of the analgesic (pain relieving) effects of nitrous oxide seems to have occurred in the late 1700s. The actual value of nitrous oxide wasn't appreciated until quite a while later. In the mid-1800s, a chemist named Gardner Colton manufactured, and then toured and demonstrated, the inhalation of nitrous oxide.
In 1845, a dentist, after seeing one of Colton's chemistry exhibitions, demonstrated the use of nitrous oxide for pain relief during dental extractions. These demonstrations by Horace Wells showed variable success. After further refinements in the manufacture and delivery processes, the value of nitrous oxide as an anesthetic (although imperfect) was eventually established. It also became clear that nitrous oxide, by itself, was not a potent enough anesthetic for more painful or involved surgeries. It became, in medicine as well as dentistry, an adjunctive agent to enhance the effects of other anesthetic agents and is still used in this manner today. It also continues to be used as an analgesic and sedative in dental offices and for minor surgical procedures.
General Anesthesia with Nitrous Oxide
WHY CAN'T NITROUS BE USED ALONE AS A GENERAL ANESTHETIC?
Nitrous oxide cannot be used by itself for general anesthesia as it is not sufficiently potent. In the operating room, nitrous oxide can be used as a pain medicine or sedative, as part of an inhalation induction or as an adjunct to other anesthesia gases.
Each anesthetic gas is assigned a value called MAC. MAC stands for "minimum alveolar concentration". A simplified explanation of the MAC of an anesthetic gas is the lowest concentration of gas in the airways that will prevent reaction to surgical incision. All of the gases, including oxygen, given during an anesthetic are part of a mixture, the sum of which equals 100 percent of the gases (obviously). To sustain life, oxygen must make up a significant portion of this mixture. Room air (the air we normally breathe) is estimated to be about 21 percent oxygen. Almost always, higher concentrations are used or needed during general anesthesia.
So, the more gas needed to prevent reaction to surgery, the higher the MAC for that gas and the lower the potency of the anesthetic. The MAC of other commonly used anesthetic gases range from under 1 percent to around 6 percent. On the other hand, the MAC of nitrous oxide is about 104 percent! Clearly, to be given at that concentration (which can't be done), no oxygen could be administered to the patient. As this is incompatible with life, nitrous oxide cannot be used by itself as a general anesthetic.
SO, WHY IS NITROUS OXIDE USED DURING GENERAL ANESTHESIA, AT ALL, THEN?
Even though nitrous oxide can't be used alone for anesthesia, it is used as a component of general anesthesia. A practice of providing "balanced anesthesia" means that several different drugs are used to complete the anesthetic. This allows lower doses of each medication to be used in order to minimize side effects and ensure that the best qualities of each agent is exploited to the best extent. Using nitrous with other anesthesia gases allows their concentration to be reduced. This is useful to decrease the side effects of those gases.
Nitrous oxide rapidly and easily crosses the membranes of the air sacs after being inhaled. Some sources refer to nitrous as a "carrier gas" because as it quickly enters the airways and then the circulation, it carries other anesthesia gases with it. This speeds any desired changes in anesthetic depth.
The inhalation induction of small children can be facilitated by nitrous oxide since it is a pleasant-smelling gas and works quickly.
These uses are further discussed below.
Other than the anesthesiologist forgetting what flavor the girl wanted :) , this shows a nice sedation with nitrous oxide.
Nitrous Oxide Effects and Uses in the Operating Room
As stated, nitrous oxide has pain blocking qualities. It induces a state of relaxation and hypnosis with a quality of dissociation. For short, non-invasive procedure, nitrous oxide may be used alone (with oxygen) to provide sedation or pain relief. Usually, it is used as part of a regimen with other medications during general anesthesia.
Small children do not tolerate having an IV placed before 'going to sleep' with anesthesia (called anesthesia induction). Instead, a child can breathe anesthesia gas for an inhalation induction. Nitrous oxide is often given before, then in addition to, a more potent anesthesia gas for this purpose. Nitrous doesn't have a bad smell like the other gases. As mentioned above, it causes a pleasant, relaxed state and allows children to drift peacefully off to sleep in most cases.
And, as mentioned, the addition of nitrous to other anesthesia gases speeds their absorption and allows changes in anesthesia depth to happen quickly.
For the health care provider, here is a link to an explanation of the concentration effect and the second-gas effect of nitrous oxide for further understanding of the chemistry and physics.
Side Effects of Nitrous Oxide
Nitrous oxide can contribute to nausea and vomiting. When given with other anesthesia gases, the risk of nausea and vomiting is additive. In patients particularly prone to postoperative nausea and vomiting, it may be best to avoid use of nitrous unless there is a compelling reason for its use.
Nitrous oxide has potential effects on cardiac physiology (how the heart works). These effects may be relevant in susceptible patients. The anesthesiologist should evaluate each case individually to decide if nitrous oxide is a suitable agent as a component of the anesthetic.
Side effects after brief or occasional use are pretty minimal. Nitrous oxide is contraindicated in certain types of surgeries, due to its ability to expand gas spaces (see below in risks).
Risks of Nitrous Oxide
The biggest risks of nitrous oxide might be to the health care professionals who are repeatedly exposed through environmental contamination. Especially when the gas is not administered in a closed system (like it is through a breathing tube from an anesthesia machine), there is significant leakage of the gas into the surrounding air. The doctors, nurses and dental staff might have more risk than a patient getting a one-time or occasional exposure. There is some evidence that working in an environment where nitrous oxide is released leads to higher rates of infertility and miscarriage.
Nitrous oxide is a greenhouse gas and is considered an environmental pollutant (despite the fact that it is found naturally in soil).
Nitrous oxide is known to interfere with DNA synthesis. Fear persists that pregnant workers (especially) exposed may subject their infants to birth defects or other problems.
Nitrous oxide diffuses into closed air spaces faster than the nitrogen component of air can diffuse out. This results in increased volume of these air spaces. In other words, any gas bubbles can rapidly expand. For most situations, this is not a problem as it will dissipate quickly after the nitrous is discontinued. But, in some situations this can be dangerous or an impediment to successful surgery.
These include, among others
- bowel obstruction (air can get in but not out and bowel that is thinned or fragile can perforate)
- air embolus (a small amount of air in the blood isn't dangerous, but a large air bubble could be if it lodges in blood vessels of organs such as the heart or brain)
- pneumothorax (air trapped outside of the lung in the chest cavity can become so large that the lungs and heart can't function)
- certain surgeries on the inner or middle ear (gas can fill the space and put pressure on, or dislodge a graft over, the eardrum, for example)
Know that these things are taken into account by the anesthesiologist before administering nitrous oxide gas. Knowing when it is and isn't safe to use certain agents is part of the anesthesiologists training and expertise.
>>>>>>>>Nitrous Oxide Outside the Operating Room<<<<<<<<
Sedation Dentistry with Nitrous Oxide: Dental Nitrous Oxide
Use of nitrous oxide at the dentist is fairly common in the United States. Dental sedation with nitrous may be available for patients with fears or phobias of the dentist, or for longer or more involved procedures.
It is usually used before, and in addition to, local anesthetics to provide a more pleasant patient experience. Nitrous oxide for this use is usually supplied in tanks mixed with oxygen so the inadvertent administration of too much nitrous with too little oxygen can be avoided.
Some U.S. centers have started using nitrous oxide for women in labor again. It is more commonly used in other countries during labor.
Use of Nitrous Oxide during Labor and Delivery
A re-emerging use of nitrous in the United States is not for general anesthesia, but as a labor pain-reliever. The practice of allowing women to self-administer nitrous oxide on an as-needed basis is used very frequently in other countries, but rarely in the US.
Unlike an epidural, nitrous does not eliminate the pain of labor. It diminishes it to a degree. For some women, this is enough to get them through the roughest parts of labor without the more invasive measure of an epidural. Others will still prefer or progress to epidural or other more significant pain relief.
Nitrous is considered to be safe during labor, when administered premixed with an adequate concentration of oxygen. It doesn't easily cross the placenta, and is therefore, not absorbed by the baby.
Nitrous Oxide Abuse and Addiction
Because of the peaceful, euphoric feeling that may sometimes be achieved with nitrous oxide, it has become a drug of abuse. Initially, this abuse was seen among health-care workers with access to nitrous (and still is), but it has become a popular chemical of abuse among teens as well. Whippets - getting high by sucking the nitrous out of an aerosol can - especially whipped cream, is still popular. However, abusers have gotten more 'sophisticated' by learning how to acquire nitrous oxide that has been placed into balloons for inhalation.
It is this population that has the biggest risk of complications from nitrous oxide. Complications include everything from brain damage due to oxygen deprivation to neurologic damage (that can cause inability to walk) to anemia and problems with formation of blood cells. Birth defects and other reproductive difficulties can also result.
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