Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: paul.fr on 16/08/2007 15:45:49
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what do they use to induce and maintain anaesthesia? I know it's commonly stated that Nitrous oxide is used, but this does not put you to sleep. So what do they use, and how long is it possible to "be under" before it becomes unsafe?
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http://en.wikipedia.org/wiki/Anaesthesia#Current_inhaled_general_anesthetic_agents
Volatile agents are specially formulated organic liquids that evaporate readily into vapors, and are given by inhalation for induction and/or maintenance of general anesthesia. Nitrous oxide and xenon are gases at room temperature rather than liquids, so they are not considered volatile agents. The ideal anesthetic vapor or gas should be non-flammable, non-explosive, lipid soluble, should possess low blood gas solubility, have no end organ (heart, liver, kidney) toxicity or side effects, should not be metabolized and should be non-irritant when inhaled by patients.
No anesthetic agent currently in use meets all these requirements. The agents in widespread current use are isoflurane, desflurane, sevoflurane, and nitrous oxide. Nitrous oxide is a common adjuvant gas, making it one of the most long-lived drugs still in current use. Because of its low potency, it cannot produce anesthesia on its own but is frequently combined with other agents. Halothane, an agent introduced in the 1950s, has been almost completely replaced in modern anesthesia practice by newer agents because of its shortcomings.[12] Partly because of its side effects, enflurane never gained widespread popularity. [12]
In theory, any inhaled anesthetic agent can be used for induction of general anesthesia. However, most of the halogenated anesthetics are irritating to the airway, perhaps leading to coughing, laryngospasm and overall difficult inductions. For this reason, the most frequently-used agent for inhalational induction is sevoflurane. All of the volatile agents can be used alone or in combination with other medications to maintain anesthesia (nitrous oxide is not potent enough to be used as a sole agent).
Currently research into the use of xenon as an anesthetic is underway, but the gas is very expensive to produce and requires special equipment for delivery, as well as special monitoring and scavenging of waste gas.
Volatile agents are frequently compared in terms of potency, which is inversely proportional to the minimum alveolar concentration. Potency is directly related to lipid solubility. This is known as the Meyer-Overton hypothesis. However, certain pharmacokinetic properties of volatile agents have become another point of comparison. Most important of those properties is known as the blood:gas partition coefficient. This concept refers to the relative solubilty of a given agent in blood. Those agents with a lower blood solubility (i.e. a lower blood:gas partition coefficient, e.g. desflurane) give the anesthesia provider greater rapidity in titrating the depth of anesthesia, and permit a more rapid emergence from the anesthetic state upon discontinuing their administration. In fact, newer volatile agents (e.g. sevoflurane, desflurane) have been popular not due to their potency [minimum alveolar concentration], but due to their versatility for a faster emergence from anesthesia, thanks to their lower blood:gas partition coefficient.
There is not, as far as I am aware, and inherent time limit on how long you may be under, but each type of anaesthetic has its own side effects (e.g. Halothane may damage the liver), and these side effects may limit the use of the specific anaesthetic after a prolonged period.
Most, probably all, general anaesthetics seem require artificial maintenance of respiration for their duration of use.
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The induction agent is different depending on the patient and the location. I'm going to assume you are asking about elective cases in the operating room, and I will stick to that in this post.
In the adult patient (who normally will have an IV), a bolus of a drug known as Propofol (a.k.a., Diprovan--same drug) is given intravenously to induce anesthesia. Depending on the procedure, other drugs may be given in addition to Propofol. These include narcotics to provide analgesia (e.g., Fentanyl) and paralytics to provide muscle relaxation (e.g., succinylcholine or rocuronium).
After induction, maintainance is necessary to keep the patient under anesthesia. In a GA (general anesthesia) in which the patient is intubated for a length of time, the most commonly used agent is an inhalant known as sevoflurane given through the endotracheal tube. Halothane is a drug that is being used less and less because of the complications mentioned above (however, see below for a caveat). If the patient is not to be intubated, a continuous infusion of Propofol is usually satisfactory to maintain sedation.
A note about Halothane Hepatotoxicity: while it is a relatively common occurrence (25-30%), there are two different classes to consider. Type I hepatotoxicity is the commonly experienced type, which results in no clinical manifestations and is a self-limiting problem that usually resolves on its own. Type II is the more dangerous one, which results in jaundice, fever, and elevated liver enzymes, eventually leading to liver failure and possibly death (50-80%); however, type II occurs in approximately 1 in 6,000-35,000 cases, making it exceptionally rare.
As far as anesthesia becoming "unsafe", it all depends on how sick you are. We do cases that last 23 hours after which there are generally no adverse effects from the anesthesia. Or, we sometimes do 30 minute cases after which the patient has a hard time breathing on his own or getting his saturation levels above 90. Anesthesia depresses your ability to breathe on your own, as well as other functions. If you have comorbidities, the time you can spend under anesthesia will decrease.
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Thank you, Paralyser, for a very interesting first post, and welcome to the forum.
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i woke up during one of my two surgeries. just long enough to try to scream (my mouth was what was being cut apart so i couldn't actually move my mouth) the doctor and the anesthesia guy both said they didn't know what happened. do you have any idea paralyzer? at first i thought it was a dream but the doctor said i really opened my eyes and jerked my head around a little and then went back out
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Interesting, I hope, in that it was informative to some extent. :)
Kdlynn: depending on how old you were at the time and what was being done, it seems that the anesthetist underestimated how much anesthesia it takes to maintain you. It is likely that they had either the gas too low or an infusion set at an improper rate. There is a monitor known as a BIS monitor that tells the anesthetist how deep the patient is under. Unfortunately, many hospitals have failed to pick up this technology.
I must say, though, that you are one of the few to whom this sort of thing has happened. I also feel that I have to commend the anesthesiologist for manning up and telling you the truth. He could easily have told you it was a dream.
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i think i confused them. lol. i remember hearing them saying i needed more of some drug right before i opened my eyes. luckily the surgeon wasn't holding a bloody scalpel above my face or anything when i woke up. i was eighteen that time and was about a hundred and fifteen pounds. it was the same people who did the first surgery when i was thirteen
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i respond strangely to medicines of all types though... so who knows
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That sounds about right. You probably started moving before you opened your eyes, alerting them that you were "not liking" the procedure, as they say. You may respond strangely to medications, but that most likely has nothing to do with this. It's just a simple case of not enough drugs.
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I had a similar experience except I was not out yet. They gave me all these shots and said I would be asleep before we got to the surgery on third floor. The anesthesiologist told me jokes all the way up! It was in the summer I Started 6th grade. I was scared to death.. It was repair work on a previous heart surgery.
They don't use Ether these days right? I had more then one sleep aid that surgery!
We got up there and he asked me to count backwards from 100 and he showed me a black mask and said this has special sleepy air called Ether it will make you sleep the big sleep!
I started counting I was still counting everyone was moving around this big drape they put over my chest. like a tent. My chest started hurting and the n it really hurt and I yelled Hey I feel that it hurts! the head of the surgeon popped up over the tent and he said Joe shes not out! He jumped up from behind me and said are you awake I said yes he said breath real deep I did he said how do you feel I said fine but it hurts! he said I know honey I 'm sorry! I will make it stop! The surgeon said get an arm board they laid my arm over this board and poked me and stated this line into my arm and injected a needle full of something into the iv thing! He said OK are you feeling OK I said yes he said breath I said OK he said hey you said you liked poems I said yes he said tell me one I did.. he said OK.. The doctor started to laugh and I remember the anesthesiologists eyes how they twinkled he was this big handsome tall black man with gorgeous eyes .. I remember looking in his eyes and feeling less scared he asked me to start counting backwords again.. we made it all the way back and he said can you count back up.. I think I got about midway and thats all she wrote. When I woke I was so bloody sick flat on my back and I remember puking violently and having ivies most of the week. The day I went home I puked all the way home it was the first time I had sat up since the surgery. I got home and was on my back for another week with my arm in a sling.. and the worst was I was sick to my stomach all week. They told me it was normal with Ether.. OOOOOH yuck.. I sleep most of the week waking to urinate in a bed pan and then out cold again..it was about 1970 ish!
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I have no idea why they would not have had you under general anesthesia for a heart operation. That seems pretty reckless to me, but they did some pretty retarded things back then. Diethyl ether is the anesthetic agent commonly known as ether; however, isoflurane and sevoflurane are also ethers. Halothane, the agent commonly used from the 50s to the 80s is not an ether. It is very disturbing to me that they did not have an IV or an a-line, let alone GA in a patient undergoing chest surgery. Of course, I wasn't even alive in 1970, so they may have done things differently then. Today, that would never happen.
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I had the big open heart when I was a bit over a year then again to correct things supposedly in 70 .. It was definitely Ether he said after wards to my mom and I that next time we have to remember she is difficult to put out! We had to give her more ether and another injection! The last surgery was last year in march of 2006,upon waking I had some disturbing trouble with something they called Strider! They wouldn't release me as I kept having these bouts and I couldn't breath.. they made me close my mouth and try to breath through my nose.. I could not breath she said it was something to do with my vocal cords swelling and the anesthetic and breathing tube.. something like that.. Do you know about that!
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Sounds like stridor. Stridor is a high-pitched noise emitted from the airway in the presence of an obstruction. It sounds like you had a laryngospasm. Sometimes the inhaled agents can irritate the larynx, causing coughing fits and sometimes laryngospasm. This usually lasts less than a minute and can be remedied by encouraging the patient to breathe while lifting the chin towards the ceiling, opening the airway.
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thats about right but it lasted off and on for a couple hours. they assured me it would pass and told me not to talk and sit up which by the way you do automatically when you can't get air! then tried breathing through nose. she said it was less harsh on the throat for whatever reason!
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I'm sorry you had to go through that, as complications of that sort is relatively uncommon in today's operating rooms. Aspiration can cause a lasting laryngospasm like what you experienced, as can a collection of mucus on the larynx. There are a variety of reasons why it could have happened, but the important thing is you pulled out of it.
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Yes I did.. Could you tell me some of the reasons why that could be caused! I would appreciate knowing..
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Laryngospasm usually occurs when fluids or mucus enter the throat, sending the larynx into spasm to prevent further accumulation of fluid in the airway and lungs, much like what happens when you drown. Laryngospasm can also occur if the breathing tube stimulates the larynx on the way out. Sometimes, however, laryngospasm is idiopathic--that is, it just happens with no identifiable cause.
There are drugs that can be used to reverse laryngospasm, so when they suctioned and performed a jaw thrust and failed to reverse the spasm, they should have considered pushing more propofol or some diazepam. They also could have used a 2% lidocaine spray.
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Paralyzer, some great answers. Thank you and welcome.
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Glad I could be of some service. Thanks for the reception.
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Laryngospasm usually occurs when fluids or mucus enter the throat, sending the larynx into spasm to prevent further accumulation of fluid in the airway and lungs, much like what happens when you drown. Laryngospasm can also occur if the breathing tube stimulates the larynx on the way out. Sometimes, however, laryngospasm is idiopathic--that is, it just happens with no identifiable cause.
There are drugs that can be used to reverse laryngospasm, so when they suctioned and performed a jaw thrust and failed to reverse the spasm, they should have considered pushing more propofol or some diazepam. They also could have used a 2% lidocaine spray.
Thanks for the the information. And I do recall them saying something about lidocaine for numbing the throat for the tube.. ..I can't remember why!
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Enjoy the site~!