Anesthesia is a partial or complete loss of sensation or feeling induced by theadministration of various substances. For many decade, people have used one formof an anesthetic during surgical procedures.
Some people also use some of theseanesthetics as recreational drugs, e. g. laughing gas (a. k. a. Nitrous Oxide).
Theterm anesthetic literally means “without feeling”. There are manydifferent types of anesthesia, but they are usually put into three groups. Thesegroups are gene- ral anesthetics, local anesthetics, and spinal anesthetics. Ageneral anesthetic causes a complete loss of consciousness. They are used whenhaving a serious operation or in the case of an emergency operation. It works tothe surgeon’s advantage because the anesthesia reacts with the body in a matterof seconds.
There are two different ways in which general anesthetics areadministered, they are intravenous and inhalation. The most popular procedure isintravenous. This is where the anesthetic is put into the body by way of aneedle in the vein, which is usually located in the hand or elbow. Althoughintravenous is more popular, it is usually used by itself during shortprocedures.
In the case of longer procedures, intravenous anesthesia is alsoaccompanied by inhalation anesthesia. Inhalation anesthesia is administered byway of a mask and in the form of gas. Usually during long procedures, the maskwill remain on while the fluids from the intravenous anesthesia work throughyour body. The second group of anesthesia is local anesthesia. Local anesthesiais used when a doctor wants to numb a certain part of the body while youmaintain total consciousness.
Local anesthetics are usually administered througha gel or cream on the surface of the skin, but can also be injected underneaththe skin, e. g. lidocane. If the anesthetic is placed on the surface of the skinthan the numbing effect should take place within a few seconds.
If injectedunderneath the skin, it can take up to a few minutes to take effect. Both formsof local anesthesia are used when dealing with minor surgery such as dentistry,etc. The third and last group of anesthetics is the topical group. This group isassociated with childbirth, gynecological procedures, and spinal operations. Aspinal injection gives relief to pain, but at the same time allows for totalconsciousness. Usually the syringe is injected into the epidural layer of thespine.
The effects of the spinal injection can be felt within minutes of theinjection. As I have already discussed, there are three different methods ofdistribution among anesthetics, inhalant, intravenous, and infusion. An inhalantis an anesthetic in the form of a gas which is administered by way of a gasmask. Intravenous anesthesia is administered by way of a needle into the vein.
Infusion anesthetics are administered by way of a catheter. These three methodsoperate in four steps. The first of these steps is premedication or inductionstage. This step involves the nurse or practitioner to administer a form of asedative or muscle relaxant. This step is not always required, only when havingmajor surgery. The second stage is when the actual anesthesia is administered.
The patient falls into a deep, pleasant state of unconsciousness. The thirdstage is when the drug is in full effect. The patient now experiences a loss ofconsciousness, although the patients reflexes still remain active and breathingis a little irregular. In the last stage, the fourth stage, the patient istotally unconscious.
Muscels are fully relaxed and breathing becomes regular andquiet. Anesthesia has a long history which started in the middle 1700’s. In1769, an English chemist, Joseph Priestley discovered the first recognizedanesthetic, nitrous oxide. Nitrous oxide is more commonly known as laughing gas. Although the gas was discovered in 1769, it wasn’t until 1844 when an Americandentist by the name of Horace Wells, first put the nitrous oxide to use during adentistry procedure.
The wonderful world of anesthesia was growing and becomingmore and more popular throughout the United States as well as in England. Thenext important discovery took place in 1829. In 1829, an American, MichealFaraday reported that the inhalation of ether caused a person to go into a stateof unconsciousness. Using ether as an anesthetic was not very popular, though.
It was first used in 1842 when, an American doctor, Crawford W. Long removed atumor off of the neck of one of his patients. The second recorded use of etherwas by the American dentist, Thomas Green Morton in 1846. Morton along with thehelp of Charles Thomas Jackson, an American chemist, devel- oped a technique forpainless tooth extraction with the assistance of diethyl ether. In 1831, anAmerican physician and chemist, Samuel Guthrie was the first to discoverchloroform and its uses.
The first to use chloroform during a surgical procedurewas Sir James Y. Simpson. Simpson was a Scottish obstetrician whom was notsatisfied with the action and reaction of ether. Simpson was the first to adoptchloroform as a useful anesthetic in surgical procedures. In 1884, Sigmund Freudwas the first to report cocaine’s anesthetic properties. An Austrailianphysician, Karl Koller, took this report of cocaine as an anesthetic and appliedit to surgical procedures.
Koller’s surgical procedure was even more importantbecause it was the first procedure to take place while using what we now call”local anesthesia”. Cocaine was the first local anesthesia to bediscovered and used in a surgical procedure. William Stewart Halsted, a profesorof surgery at John Hopkins University in Baltimore, was the first to use cocaineto anesthetize whole areas of the body by directly injecting the cocaine intothe nerve. In 1898, Karl Gustav Bier injected cocaine into vertebral canal andobtained paralysis of the lower extremities of the body.
He used this method insurgical procedures. Since then this procedure that he discovered is know asspinal anesthesia and is widely used today. At around 1901, J. L.
Corning usedcocaine to produce a useful spinal anesthetic, which in turn produced twoimportant cocaine derivatives, novocaine and procaine. Many other importantanalgesics and their uses came about between 1800 to 1900. Ethyl chloride whichwas introduced to us in 1848, was too short lived. Surgeons needed an anesth-etic that was non-toxic and non-inflammable. So in 1929, cyclopropane wasintroduced to the medical world, but soon enough the medical world found outthat the drug was inflammable.
In 1934, trichloreth- ylene was first used. Thisdrug on the other hand came along with two advantages. It reduced the awarenessof pain while maintaining full consciousness, which made the drug ideal forchildbirth use. In 1874, Ore of Bordeaux, was the first to achieve anintravenous anesthesia. He used Chloral to achieve this intravenous anesthesia.
In 1902, Emil Fischer performed a synthesis of Veronal. The synthesis caused theuse of intravenous anesthesia to be widely excepted and performed. After Veronalmany other analgesics were produced and discovered. After 1945, two specificdrugs came into use with anesthesia. These two drugs are curare andsuccinylcholine. Both of these drugs are used in anesthetics as a muscle relaxer.
Curare prevents the nervous impulses fromreaching the muscels. Thus blocking theit at the neuromuscular junction where the nerve transmitter substance,acetylcholine, is stored. The curare that is used in anesthesia is refered to astubocurarine. Succinylcholine is used to neutralize the action of acetylcholinein the neuromuscular junction. These anesthetics and their derivatives are stillused today.
Another form of anesthetic used on the body is hypothermia. This iswhere the body temperature is lowered by about ten degrees. Hypothermia isachieved by cooling the patient with ice, wet sheets, and fans. Although thishelps in cooling the body it does not stop the body’s natural responses to thecold. These responses are centered around the part of the brain called thehypothalamus.
Some of these responses are shivering, etc. The body has theseresponses because it is trying to keep the body’s heart, temperature, and bloodpumping at a constant rate. In order to stop these responses doctors use a drugcalled chlorpromazine or they use promethazine, which also has a tranquilizingeffect. This whole process is used because it lowers the amount of oxygenconsumed by the tissues in the body. This also causes vital organs in the bodyto consume a lower amount of oxygen.
The less oxygen the smaller amount of bloodthat is rushed to the brain and other vital organs within the body duringsurgery. In turn the brain and other vital organs will still function just at aslower pace. This is an advantage to brain and heart surgery because theseoperations require more time and this allows for it without causing permanentdamage to the body. There are many different effects of anesthesia on the body.
There can be a dramatic drop or rise in blood pressure. A person’s bloodpressure may also drop or rise if the patient goes into shock or has lost toomuch blood. Some anesthetics cause nausea and sickness. A rare reaction thatsometimes occurs when administered general anesthesia is juandice. Doctors tryto choose an anesthetic that induces unconsciousness rapidly and has the leastamount of side effects. Throughout the country there are many different types ofanesthetics used.
Some of the most popular anesthetics are used in U. S. hospitals across the region. Among general anesthetics, cyclopropane, ethylene,and halothane are the most popular. Cyclopropane and ethylene are used withcaution because they are highly explosive.
Halothane is the most prefered overthe three because it is neither inflammable or explosive. Amongst intravenousanesthesia, Pentothal sodium is the most popular. This is because it producesthe least amount of side effects during and after a surgical procedure. Blockanesthesia is the most common and popular of the group known as localanesthetics.
Block anesthesia is often called this because it blocks the nerves,to that specific area, off so that the patient feels no pain within thatimmediate area. The two most popular types of block anesthesia are spinal andcaudal. They are both administered during the child bearing process. The mostcommon drug used in these blocks are procaine hydrochloride. As far as topicalanesthetics go, xylocaine is the most popular. It is used extensively when thepatient is receiving stitches or going through simple dentistry procedure.
Theseare among the most useful and important in the anesthetic industry. Since theearly 18th century, many advances have been made in the field of anesthetics. Inhalation anesthesia has had three main advances in the course of its history. These advances include sevflurane, desflurane, and xenon.
Sevoflurane was firstsynthesized in 1960, but has just recently become widely distributed for generaluse. Sevoflurane is a methylpropyl ether because it is highly insoluble. Forexample it is three times more soluble in blood than halothane is. Since sevofl-urane has low solubility, it enables the anesthesia to act faster in the humanbody. Recovery from sevo- flurane is also rapid. When inhaling sevoflurane itdoes not irritate the airways.
This allows a rapid as well as pleasant inductionand awakening. Sevoflurane has become extremely popular, especially amongchildren. There is a downfall however, it is too expensive to produce in largequantities. Desflurane was also first synthesized in 1960, but has just recentlybeen introduced to the medical world. Basically, des- flurane has the sameproperties as sevoflurane, but it is an irritant to the airways when inhaled.
Over 50% of the people who use this product develop some form of laryngospasm. Although this is a major down fall, the drug is very inexpensive to produce. This allows for more research to be done to improve the drug because there is agreater amount of left over funds after producing the drug. Xenon, anotherimportant inhalant, is an inert gas.
Xenon is still prohibited for medical usebecause it is a fairly new discovered drug that seems to have anestheticproperties. It is extremely insoluble in the blood. This causes it to have anextremely fast induction and recovery. It is not extremely potent when it isused by itself, but could someday replace nitrous oxide as a general anesthetic. Xenon exhibits all the analgesic properties to eventually become an importantanesthetic in the medical world. Many advances have also been made tointravenous anesthetics as well.
One of the newest types of intravenousanethesia is propofol. It is the newest intravenous drug to date. It wasintroduced to the medical world in 1984. Since then there have been incredibleadvances made in the administration, distribution, and maintenance of the drug,propofol. The drug has very few side effects, which include a mere nausea anddrowsiness.
It has a very fast recovery and induction. One major disadvantage,though, is that it is difficult to acheive the desired plasma concentration bymanual control of the infusion rate. In order to maintain a constant flow theinfusion rate must be changed frequently. This is when the target controlledinfusion rate technique takes place.
Target controlled infusion is what allowsthe anesthesiologist to set a desired plasma concen- tration, which the softwareinside the infusion pump produces rapidly, but safely by controlling theinfusion rate according to complex, but standard pharmacokinetic equations(basically medical equations). Remifentanil is a new potent, yet synthetic opiodthat is ideally suited for infusion during anesthesia. Unlike other opiods,remifentanil contains a methyl ester in its structure which causes a rapidmetabolism of the drug within the body. Remifentanil is now used as aneuroanesthetic and in the future will probably be used as a cardiac andcardiovascular anesthetic.
Many advances have also been made in the medicalworld concerning local anesthetics. Amongst these local anesthetics, the mostpopular and up to date are bupivacaine and ropivacaine. Bupivacaine isfrequently used in postoperative pain releif. Induction to this anesthetic israpid and lasts very long. It can last for several hours depending on the dosegiven. The bupivacaine molecule exhibits stereoisomerism in each one of the twoenantiomers, which are R(+)bupivacaine and S(-) bupivacaine.
The R(+) form ofbupivacaine is 3-4 times more likely to cause cardiovascular toxitity in rabitts,sheep, and humans. Ripovacaine is very similar to bupivacaine, but it is onlyprepared as S(-) ripovacaine isomer. Ripovacaine was proven safer thanbupivacaine in many clinical studies. Anesthesia has an unusual property.
It isknown as the cutoff phenom- enon. The cutoff refers to the loss of anestheticpotency in the homologous series of alkanes and their derivatives when theirsize becomes too large. Apparently the potency increases with the length of thechain until the chain reaches fourteen carbons. At the fourteen carbon mark, theanesthetic has no potency whatsoever. The anesthetic potency increases rapidlyfrom a two carbon chain (ethanol) up to a ten carbon chain (decanol).
From theeleven carbon chain to the thirteenth carbon chain the potency remains the same. When the carbon chain finally reaches the forteenth carbon, the potency suddenlydisappears. Scientists predict that this happens because the binding site is notlarge enough to accomodate long chained alcohols or because of the low watersolubility of longer 1- alkanols limits their access to the action sight. Scientists studied this through changing the 1- alkanol series to DPPC (dipalmitoyl-L-a-phosphatidylcholine). They did this through a procedure known ashydrogen bonding.
Through hydrogen bonding transitional phases occured. In thesephases scientists proved that in between the transition of temperature, whichalso changed the state of matter, there was a certain point at which there wasno affect on the DPPC. Scientists also learned that the primary action site foranesthetics are the macromolecules of water. In conclusion C2-C10 are known asanesthetics and C14+ are known as nonanesthetics.
In anesthesia, highpolarizability causes hydrogen bond breaking which causes anesthesia to work(e. g. cyclopropane). Also increased hydrophobicity along with relaxaion ofmembranes and proteins cause anesthesia to work. Anesthetics have manyadvantages. They are great in eliviating pain before, during, and after asurgical procedure.
They also make the procedures much more easier. Anestheticsgive a desired affect which is good because it helps us as a patient to relaxand feel calm and pleasant. Anesthetics have been around since the begging ofthe 1700’s. Scientists have gathered a tremendous amount of informationconcerning anesthetics.
Many advancements have been made and will continue to bemade. Throughout history man has searched for a way to stop pain. Whether it bea sore tooth or a broken limb, man has tried many different things to try and toget rid of that pain that he feels. The most modern way to eliviate pain isthrough the use of anesthetics. Although many of them have side effects, theyare improving and as long as our world and economy keep moving ahead andtechnologically advancing, we will be able to perfect all of the anesthetics.
Inthe future there will prob- ably be new techniques used to administer anddistribute anesthetics, but for now these drugs seem to be doing the trick. Aswe enter into this new millennium, I hope to see more advances concerninganesthesia in this colorful world that we call the U. S. BibliographyAnesthesia: The Curing Sleep.
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