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Anesthetics


Anesthesia is a partial or complete loss of sensation or feeling induced by the
administration of various substances. For many decade, people have used one form
of an anesthetic during surgical procedures. Some people also use some of these
anesthetics as recreational drugs, e.g. laughing gas (a.k.a. Nitrous Oxide). The
term anesthetic literally means "without feeling". There are many
different types of anesthesia, but they are usually put into three groups. These
groups are gene- ral anesthetics, local anesthetics, and spinal anesthetics. A
general anesthetic causes a complete loss of consciousness. They are used when
having a serious operation or in the case of an emergency operation. It works to
the surgeon's advantage because the anesthesia reacts with the body in a matter
of seconds. There are two different ways in which general anesthetics are
administered, they are intravenous and inhalation. The most popular procedure is
intravenous. This is where the anesthetic is put into the body by way of a
needle in the vein, which is usually located in the hand or elbow. Although
intravenous is more popular, it is usually used by itself during short
procedures. In the case of longer procedures, intravenous anesthesia is also
accompanied by inhalation anesthesia. Inhalation anesthesia is administered by
way of a mask and in the form of gas. Usually during long procedures, the mask
will remain on while the fluids from the intravenous anesthesia work through
your body. The second group of anesthesia is local anesthesia. Local anesthesia
is used when a doctor wants to numb a certain part of the body while you
maintain total consciousness. Local anesthetics are usually administered through
a gel or cream on the surface of the skin, but can also be injected underneath
the skin, e.g. lidocane. If the anesthetic is placed on the surface of the skin
than the numbing effect should take place within a few seconds. If injected
underneath the skin, it can take up to a few minutes to take effect. Both forms
of 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 is
associated with childbirth, gynecological procedures, and spinal operations. A
spinal injection gives relief to pain, but at the same time allows for total
consciousness. Usually the syringe is injected into the epidural layer of the
spine. The effects of the spinal injection can be felt within minutes of the
injection. As I have already discussed, there are three different methods of
distribution among anesthetics, inhalant, intravenous, and infusion. An inhalant
is an anesthetic in the form of a gas which is administered by way of a gas
mask. Intravenous anesthesia is administered by way of a needle into the vein.

Infusion anesthetics are administered by way of a catheter. These three methods
operate in four steps. The first of these steps is premedication or induction
stage. This step involves the nurse or practitioner to administer a form of a
sedative or muscle relaxant. This step is not always required, only when having
major surgery. The second stage is when the actual anesthesia is administered.

The patient falls into a deep, pleasant state of unconsciousness. The third
stage is when the drug is in full effect. The patient now experiences a loss of
consciousness, although the patients reflexes still remain active and breathing
is a little irregular. In the last stage, the fourth stage, the patient is
totally unconscious. Muscels are fully relaxed and breathing becomes regular and
quiet. Anesthesia has a long history which started in the middle 1700's. In

1769, an English chemist, Joseph Priestley discovered the first recognized
anesthetic, 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 American
dentist by the name of Horace Wells, first put the nitrous oxide to use during a
dentistry procedure. The wonderful world of anesthesia was growing and becoming
more and more popular throughout the United States as well as in England. The
next important discovery took place in 1829. In 1829, an American, Micheal

Faraday reported that the inhalation of ether caused a person to go into a state
of 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 a
tumor off of the neck of one of his patients. The second recorded use of ether
was by the American dentist, Thomas Green Morton in 1846. Morton along with the
help of Charles Thomas Jackson, an American chemist, devel- oped a technique for
painless tooth extraction with the assistance of diethyl ether. In 1831, an

American physician and chemist, Samuel Guthrie was the first to discover
chloroform and its uses. The first to use chloroform during a surgical procedure
was Sir James Y. Simpson. Simpson was a Scottish obstetrician whom was not
satisfied with the action and reaction of ether. Simpson was the first to adopt
chloroform as a useful anesthetic in surgical procedures. In 1884, Sigmund Freud
was the first to report cocaine's anesthetic properties. An Austrailian
physician, Karl Koller, took this report of cocaine as an anesthetic and applied
it to surgical procedures. Koller's surgical procedure was even more important
because it was the first procedure to take place while using what we now call
"local anesthesia". Cocaine was the first local anesthesia to be
discovered and used in a surgical procedure. William Stewart Halsted, a profesor
of surgery at John Hopkins University in Baltimore, was the first to use cocaine
to anesthetize whole areas of the body by directly injecting the cocaine into
the nerve. In 1898, Karl Gustav Bier injected cocaine into vertebral canal and
obtained paralysis of the lower extremities of the body. He used this method in
surgical procedures. Since then this procedure that he discovered is know as
spinal anesthesia and is widely used today. At around 1901, J.L. Corning used
cocaine to produce a useful spinal anesthetic, which in turn produced two
important cocaine derivatives, novocaine and procaine. Many other important
analgesics and their uses came about between 1800 to 1900. Ethyl chloride which
was 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 was
introduced to the medical world, but soon enough the medical world found out
that the drug was inflammable. In 1934, trichloreth- ylene was first used. This
drug on the other hand came along with two advantages. It reduced the awareness
of pain while maintaining full consciousness, which made the drug ideal for
childbirth use. In 1874, Ore of Bordeaux, was the first to achieve an
intravenous anesthesia. He used Chloral to achieve this intravenous anesthesia.

In 1902, Emil Fischer performed a synthesis of Veronal. The synthesis caused the
use of intravenous anesthesia to be widely excepted and performed. After Veronal
many other analgesics were produced and discovered. After 1945, two specific
drugs came into use with anesthesia. These two drugs are curare and
succinylcholine. Both of these drugs are used in anesthetics as a muscle relaxer.

Curare prevents the nervous impulses fromreaching the muscels. Thus blocking the
it at the neuromuscular junction where the nerve transmitter substance,
acetylcholine, is stored. The curare that is used in anesthesia is refered to as
tubocurarine. Succinylcholine is used to neutralize the action of acetylcholine
in the neuromuscular junction. These anesthetics and their derivatives are still
used today. Another form of anesthetic used on the body is hypothermia. This is
where the body temperature is lowered by about ten degrees. Hypothermia is
achieved by cooling the patient with ice, wet sheets, and fans. Although this
helps in cooling the body it does not stop the body's natural responses to the
cold. These responses are centered around the part of the brain called the
hypothalamus. Some of these responses are shivering, etc. The body has these
responses because it is trying to keep the body's heart, temperature, and blood
pumping at a constant rate. In order to stop these responses doctors use a drug
called chlorpromazine or they use promethazine, which also has a tranquilizing
effect. This whole process is used because it lowers the amount of oxygen
consumed by the tissues in the body. This also causes vital organs in the body
to consume a lower amount of oxygen. The less oxygen the smaller amount of blood
that is rushed to the brain and other vital organs within the body during
surgery. In turn the brain and other vital organs will still function just at a
slower pace. This is an advantage to brain and heart surgery because these
operations require more time and this allows for it without causing permanent
damage 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 blood
pressure may also drop or rise if the patient goes into shock or has lost too
much blood. Some anesthetics cause nausea and sickness. A rare reaction that
sometimes occurs when administered general anesthesia is juandice. Doctors try
to choose an anesthetic that induces unconsciousness rapidly and has the least
amount of side effects. Throughout the country there are many different types of
anesthetics 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 with
caution because they are highly explosive. Halothane is the most prefered over
the three because it is neither inflammable or explosive. Amongst intravenous
anesthesia, Pentothal sodium is the most popular. This is because it produces
the least amount of side effects during and after a surgical procedure. Block
anesthesia is the most common and popular of the group known as local
anesthetics. Block anesthesia is often called this because it blocks the nerves,
to that specific area, off so that the patient feels no pain within that
immediate area. The two most popular types of block anesthesia are spinal and
caudal. They are both administered during the child bearing process. The most
common drug used in these blocks are procaine hydrochloride. As far as topical
anesthetics go, xylocaine is the most popular. It is used extensively when the
patient is receiving stitches or going through simple dentistry procedure. These
are among the most useful and important in the anesthetic industry. Since the
early 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 first
synthesized in 1960, but has just recently become widely distributed for general
use. Sevoflurane is a methylpropyl ether because it is highly insoluble. For
example 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 human
body. Recovery from sevo- flurane is also rapid. When inhaling sevoflurane it
does not irritate the airways. This allows a rapid as well as pleasant induction
and awakening. Sevoflurane has become extremely popular, especially among
children. There is a downfall however, it is too expensive to produce in large
quantities. Desflurane was also first synthesized in 1960, but has just recently
been introduced to the medical world. Basically, des- flurane has the same
properties 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 a
greater amount of left over funds after producing the drug. Xenon, another
important inhalant, is an inert gas. Xenon is still prohibited for medical use
because it is a fairly new discovered drug that seems to have anesthetic
properties. It is extremely insoluble in the blood. This causes it to have an
extremely fast induction and recovery. It is not extremely potent when it is
used by itself, but could someday replace nitrous oxide as a general anesthetic.

Xenon exhibits all the analgesic properties to eventually become an important
anesthetic in the medical world. Many advances have also been made to
intravenous anesthetics as well. One of the newest types of intravenous
anethesia is propofol. It is the newest intravenous drug to date. It was
introduced to the medical world in 1984. Since then there have been incredible
advances made in the administration, distribution, and maintenance of the drug,
propofol. The drug has very few side effects, which include a mere nausea and
drowsiness. It has a very fast recovery and induction. One major disadvantage,
though, is that it is difficult to acheive the desired plasma concentration by
manual control of the infusion rate. In order to maintain a constant flow the
infusion rate must be changed frequently. This is when the target controlled
infusion rate technique takes place. Target controlled infusion is what allows
the anesthesiologist to set a desired plasma concen- tration, which the software
inside the infusion pump produces rapidly, but safely by controlling the
infusion rate according to complex, but standard pharmacokinetic equations
(basically medical equations). Remifentanil is a new potent, yet synthetic opiod
that is ideally suited for infusion during anesthesia. Unlike other opiods,
remifentanil contains a methyl ester in its structure which causes a rapid
metabolism of the drug within the body. Remifentanil is now used as a
neuroanesthetic and in the future will probably be used as a cardiac and
cardiovascular anesthetic. Many advances have also been made in the medical
world concerning local anesthetics. Amongst these local anesthetics, the most
popular and up to date are bupivacaine and ropivacaine. Bupivacaine is
frequently used in postoperative pain releif. Induction to this anesthetic is
rapid and lasts very long. It can last for several hours depending on the dose
given. The bupivacaine molecule exhibits stereoisomerism in each one of the two
enantiomers, which are R(+)bupivacaine and S(-) bupivacaine. The R(+) form of
bupivacaine is 3-4 times more likely to cause cardiovascular toxitity in rabitts,
sheep, and humans. Ripovacaine is very similar to bupivacaine, but it is only
prepared as S(-) ripovacaine isomer. Ripovacaine was proven safer than
bupivacaine in many clinical studies. Anesthesia has an unusual property. It is
known as the cutoff phenom- enon. The cutoff refers to the loss of anesthetic
potency in the homologous series of alkanes and their derivatives when their
size becomes too large. Apparently the potency increases with the length of the
chain until the chain reaches fourteen carbons. At the fourteen carbon mark, the
anesthetic has no potency whatsoever. The anesthetic potency increases rapidly
from a two carbon chain (ethanol) up to a ten carbon chain (decanol). From the
eleven carbon chain to the thirteenth carbon chain the potency remains the same.

When the carbon chain finally reaches the forteenth carbon, the potency suddenly
disappears. Scientists predict that this happens because the binding site is not
large enough to accomodate long chained alcohols or because of the low water
solubility 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 as
hydrogen bonding. Through hydrogen bonding transitional phases occured. In these
phases scientists proved that in between the transition of temperature, which
also changed the state of matter, there was a certain point at which there was
no affect on the DPPC. Scientists also learned that the primary action site for
anesthetics are the macromolecules of water. In conclusion C2-C10 are known as
anesthetics and C14+ are known as nonanesthetics. In anesthesia, high
polarizability causes hydrogen bond breaking which causes anesthesia to work
(e.g. cyclopropane). Also increased hydrophobicity along with relaxaion of
membranes and proteins cause anesthesia to work. Anesthetics have many
advantages. They are great in eliviating pain before, during, and after a
surgical procedure. They also make the procedures much more easier. Anesthetics
give a desired affect which is good because it helps us as a patient to relax
and feel calm and pleasant. Anesthetics have been around since the begging of
the 1700's. Scientists have gathered a tremendous amount of information
concerning anesthetics. Many advancements have been made and will continue to be
made. Throughout history man has searched for a way to stop pain. Whether it be
a sore tooth or a broken limb, man has tried many different things to try and to
get rid of that pain that he feels. The most modern way to eliviate pain is
through the use of anesthetics. Although many of them have side effects, they
are improving and as long as our world and economy keep moving ahead and
technologically advancing, we will be able to perfect all of the anesthetics. In
the future there will prob- ably be new techniques used to administer and
distribute anesthetics, but for now these drugs seem to be doing the trick. As
we enter into this new millennium, I hope to see more advances concerning
anesthesia in this colorful world that we call the U.S.

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