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History
Introduction
to the anaesthesia
Types
of the anaesthesia
Drugs
of the general anaesthesia
Accidents
and incidents
History
The anaesthesia
is a hundred and fifty years old of existence, and,
as you can suspect it, it radically transformed surgical
art. Indeed, before the anaesthesia, the doctor did
not have an other resource to only operate with sharp.
The pain and the stress were often fatal to the patient,
and the surgeon was to operate as soon as possible.
It is of this time that the surgeon holds his reputation
of dexterity and speed, because these two qualities
were essential with the good success of an operation:
a good surgeon was to work quickly and well if he wanted
to keep his patient in life.
Before
the anaesthesia, one tried to deaden people as it could,
by using alcohol or drugs, like the belladonna. When
there were not other solutions, they firmly were attached,
in particular when it was necessary to proceed to amputations
or dental interventions.
It should not be forgotten that the surgeon not only
did not have anaesthesia, but that there was neither
blood transfusion either nor antibiotics. A fortiori,
the doctor especially did not have either the sophisticated
equipment which now makes it possible to carry out unimaginable
interventions one century ago, in vascular or orthopedic
surgery.
The
anaesthesia historically played an essential part in
the evolution of the surgery, because by removing the
suffering, it made it possible to the surgeon to more
calmly work and more slowly, and thus to improve its
techniques.
Introduction to the anaesthesia
A. Definition of the anaesthesia.
"Anaesthesia" means deprivation of feelings. The goal
of the anaesthesias is to remove the pain, but also
any other impulse related to an instrumental aggression,
all "nociception". At a comatose subject, occurred of
circulatory modifications can testify to a nociception.
B. Various modes of anaesthesia.
The anaesthesia can be obtained: (1) by an infiltration
of fabrics and their receivers with anaesthetic buildings;
(2) by a loco-regional tronculaire or plexic infiltration
upstream; (3) by the dépot of Al to the direct or indirect
contact of the spinal cord; (4) by a general activity
on all the névraxe thanks to anaesthetic Generals or
selective.
C. The anaesthesia obeys the laws of the pharmacokinetic
one.
The depth of the anaesthesia depends on the concentration
of drugs obtained in nervous fabrics, or plasma. For
each anaesthetic drug, there is a minimal concentration
effective CME.
The disappearance of the anaesthetic molecules of the
place of their action is done either by redistribution
in close fabrics or blood, or by local, blood or hepatic
biotransformation. The decrease of the concentration
of anaesthetic is exponential according to time.
D. The anaesthesia obeys the laws of pharmacodynamics.
The anaesthesia is not obtained with the same amount
of drug at each individual. By analogy with the "Effective
Amount 50" (OF 50), the "Minimal Alveolar Concentration"
(MAC) is the concentration of anaesthetic gas or volatile
inhaled which is effective at 50% of the subjects. A
small variation of concentration or intravenous amount
can make pass this percentage from 50 to 75% or to 25%.
Many anaesthetic have a weak report/ratio "Proportions
Lethal 50"/OF 50.
Types of the anaesthesia
A. Local anaesthesia & loco-regional
In this type of anaesthesia, the principle is that of
the anaesthesia of contact between drug and nervous
fibre. As we already underlined, the anaesthetic product
is known for a long time, since it acts of a derivative
of cocaine. The anaesthetic ones currently used have
as a name: Xylocaïne *, Marcaïne *, Duranest *, or Citanest
*, Pontocaïne *. In the local anaesthesia, one anaesthetizes
only the place which one wants to open, for example
a tooth and the part of corresponding gum. The loco-regional
anaesthesia concerns, it, a whole area, all the territory
innervé by a nervous trunk.
The local anaesthesias and loco-regional are used for
the small located operations, for example on the level
of the hands, the feet, teeth etc. But all the operations
are likely to profit from this type of anaesthesia.
B. Local anaesthesia
The local anaesthesia is known, and the majority among
you probably already underwent one of them. It takes
only a few minutes: it is enough to inject Xylocaïne
* in the zone to be operated using a very fine needle.
C. Regional anaesthesia
To carry out a regional anaesthesia, there are several
techniques. The first is the local anaesthesia into
intravenous under garrot (it is the anaesthesia known
as "Canadian"). One places a garrot at the root of the
member, and one injects into the veins a diluted solution
of local anaesthetic. The anaesthesia tronculaire consists
in injecting the anaesthetic near a nervous plexus,
for example in the armpit, the groin, or on the level
of the neck.
D. Rachianesthesy
The anaesthesia most commonly practised is the rachidian
anaesthesia or rachianesthesy. It consists in carrying
out a lumbar puncture (index, complementary Examens)
below the first lumbar vertebra (above, there is risk
to injure the spinal cord), then to inject into the
céphalo-rachidian liquid a local anaesthetic solution
which involves a paralysis of the lower part of the
body.
This anaesthesia is used for the operations of the urinary
tract, in gynaecology-obstetrics, and for the orthopedic
operations of the lower limb (knee, ankle, etc). One
can carry it out by carrying out a single injection.
It acts of a fast and powerful anaesthesia, but that
one cannot prolong. There is a technique uninterrupted:
one introduces a microcathéter (small catheter) into
the rachidian channel what makes it possible to maintain
the anaesthesia. But this technique has a disadvantage:
there is a risk of infection and escape of the céphalo-rachidian
liquid at the time of the ablation of the catheter (with
danger of cephalgia).
E. Péridurale
The anaesthesia péridurale consists in practising a
puncture carried out with a needle a little larger than
that used for the rachianesthesy. The various méningées
barriers are not crossed, because one respects the dura
mater, the most external layer of the fibrous envelopes
which surround nervous fabric (index, Anatomie of the
nervous system). One injects the anaesthetic in space
péridural, i.e. outside the dura mater. This anaesthesia
is less dangerous and makes it possible to set up a
catheter of larger diameter. If, owing to the fact that
one remains apart from the meninges, the anaesthetic
effect is felt less quickly, it lasts, on the other
hand, longer.
The advantage of this technique, compared to the rachianesthesy,
is that one can practise it on all the floors of the
spinal cord, since the needle is planted apart from
the dura mater.
Thus an injection will be made: - at the dorso-lumbar
level for the digestive and thoracic surgery; - at the
cervical level for the surgery of the upper limb, the
thorax, the centres or the arteries carotids; - at the
lumbar level for the same indications as the rachianesthesy
like for the indications obstétricales; - on the level
of the sacrum, by applying the technique of the caudal
anaesthesia, used in pediatry for urologic operations.
There are some counter-indications which make impossible
this type of anaesthesia: - the refusal of the patient:
you have perfectly the choice and freedom to prefer
a general anaesthesia, except if your health makes preferable
a local anaesthesia; - a disorder of blood coagulation
(index, Hematology); - an infectious hearth (furoncle,
for example) at the place of the injection; - an evolutionary
neurological disease, like a multiple sclerosis; - epilepsy
and convulsions; - an allergy to the anaesthetic buildings.
Drugs of the general anaesthesia
With. Anaesthetic volatile
and gas Generals.
They are, today, the nitrogen protoxide
(N2O), and the halogenous ones: the halothane (* Fluothane),
the enflurane (* Ethrane)et the isoflurane (* Forane).
They can be enough to anaesthetize operated.
With 1: Modes of action.
After inhalation, alvéolo-capillary transfer, cardiac
redistribution towards richly vascularized fabrics,
they penetrate in the lipidic membranes of which they
modify the physical characteristics, inhibiting the
ionic movements and consequently synaptic conduction
or exitability and the cardiac contractile force. They
have effects total and aspecific on all the cells, but
for variable concentrations. Anaesthesia occurs when
a certain number of sites of nervous action are blocked,
which occurs for an alveolar concentration given, slightly
higher than MAC (cf 1.4.) The anaesthesia is maintained
by preserving the same alveolar, and thus tissue concentration.
The alarm clock is obtained for alveolar concentrations
of anaesthetic lower than 20% of MAC. These anaesthetic
has additive effects between them.
With 2: General properties.
Their power and their time of action are related to
their physicochemical properties for example the critical
temperature and solubility in greases. The N2O is not
very powerful, not very soluble but fast of action,
the halothane is powerful, very soluble in greases but
slower of action.
They depress all the cerebral activity, the neuro-transmission,
the aéro-digestive reflexes, the muscular tone, the
vegetative reactivity with the nociception, thermoregulation,
ventilation, the cardiac flow, vasomotor tonicity, the
hepatic and renal perfusion, hormonal secretion. They
cause a reversible coma. Their action thus requires
the catch of load by the anaesthetist of ventilation
as well as interventions on the hémodynamique one.
They can have a certain toxicity on the liver, the kidneys
and at certain genetically predisposed subjects (porphyritic,
myopathes...).
B. The anaesthetic intravenous ones.
They are the hypnotic ones which, with
strong amounts, causes a coma with disappearance of
the aéro-digestive reflexes, ventilatory and circulatory
depression, little analgesia and little muscular hypotonia.
They are not enough with the surgical anaesthesia. They
differ the ones from the others.
* The thiopental (* Penthotal, * Nesdonal) is an ultra-short
barbiturate. It is one anticonvulsivant. It causes apnea.
Only, it does not allow intubation. It entraine of the
allergies in 1 case for 500, approximately. It worsens
the porphyries. It is metabolized by the liver. It is
of a rather sure employment to the amount of 5 mg/kg-1,
with re-injections of half proportions the every 10
to 30 minutes.
* The propofol (* Diprivan), recent, provides an anaesthesia
more complete than the precedent. It causes apnea, a
ventilatory and cardiovascular depression marked. It
allows the exposure of the glottis but not intubation.
It entraine only few allergies. It is metabolized by
the liver. It is managed with the initial amount of
2 mg/kg-1 then from 5 to 7 mg/kg-1.h-1 in perfusion.
* The étomidate provides a light anaesthesia, with apnea
and moderated hypoventilation, but it is neither circulatory
depressor nor allergenic, from where its intéret at
the insufficient circulatory one and the atopique one.
Metabolized by the liver, it is managed with the amount
of 0,4 mg/kg-1 to induction.
* The kétamine is a drug with share which causes a state
of catalepsy, analgesia and an amnesia, without true
hypnosis. The alarm clock is often marked by dreams,
hallucinations. Its moderate respiratory effects, and
its effect adrenergic make it useful in country under-médicalisé.
The amount of induction is 2 mg/kg-1 into IV or 7 Mg
into IM. It acts during 15 minutes. A premedication
of atropine and benzodiazepine is essential.
* Benzodiazepines make it possible to potentiate the
anaesthesia or to initiate an induction. Among them,
the flunitrazépam (1 to 2 Mg IV), the midazolam 2 to
5 Mg IV are used.
C. The morphine ones
The preceding drugs being little analgésiants, except
the kétamine, the majority of the general anaesthesias
claim the morphine ones, all major, slightly sedative
ventilatory depressors and veinodilatateurs. The fentanyl,
with the amount of 5 ug/kg-1 in 3 H entraine not of
residual hypoventilation. Morphine (0,3 mg/kg-1), pethidine
(* Dolosal 1 to 2 mg/kg-1) still have their place. The
naloxone (* Narcan 5 to 10 ug/kg-1) makes it possible
to treat the anaesthetic overdoses.
D. Curares
The competitive curares of acetylcholine block the neuro-muscular
junction. They are antagonisables by the prostigmine
(1 to 3 Mg after atropine 1 Mg). They cause a complete
and durable ventilatory paralysis, which becomes lighter
little by little. Their use with effective amount for
a good abdominal relaxation requires controlled ventilation
and intubation trachéale.
Water-soluble, they have a low volume of distribution
and are eliminated primarily by the kidneys. Their duration
of action varies from 20 to 50 minutes. The pancuronium
and the vecuronium get busy with the amount of 0,1 mg/kg-1
which allows intubation. The atracurium is destroyed
in plasma by the reaction of Hoffman.
The suxaméthonium (* Célocurine, 1 mg/kg-1) acts like
acetylcholine by depolarizing the driving plate. Of
fast action, it is less and less used, because allergenic
and hyperkaliémiant.
Accidents and incidents
The
anaesthesia is not an act pain-killer, and it can generate
accidents, sometimes serious. But you do not alarm,
these accidents are very rare. Here some of those which
can occur. - shocks anaphylactic :
they are the most serious accidents and most unforeseeable,
caused by the anaesthetic products. Chloroform was formerly
responsible for many heart diseases, in particular of
ventricular fibrillations (index, Troubles of the rate/rhythm).
- the hypoventilation is the most frequent
accident nowadays, characterized by an insufficient
breathing for oxygenating blood enough. The hypoventilation
often occurs during the operation; it can have various
origins: a defect of monitoring, an accidental disconnection
of the feeder pipes, a bronchial obstruction, the presence
of a foreign body or vomiting in the bronchi. - the
heart failure: it can be caused by a massive haemorrhage
during the operation, or by a hypothermia (drops too
important internal temperature). - the gas embolism
: a gas bubble can be formed in the vessels and move
until in the brain where it is likely to cause a serious
cerebral vascular accident. This accident can occur
in the interventions where one insufflates carbon dioxide
in the organization, for example at the time of the
c?lioscopies. - the amniotic embolism
obeys the same principle. A fragment of placenta can
migrate in the vessels at the time of an intervention
of obstetrics or of a Caesarean. - the fibrino-cruoric
embolism : a blood clot is formed sometimes
very quickly during an intervention and being at the
origin of a massive pulmonary embolism.
Let
us specify that these accidents are not caused by the
anaesthesia itself, but, if they take place during the
operation, it is the role of the anaesthetist to deal
with them and to adopt all the suitable measures to
look after them. - the coma is the most serious consequence
of these accidents, apart from the death. In the event
of coma, by definition, the patient does not awake after
the operation, in spite of all the man?uvres of reanimation.
The coma is in general secondary with a circulatory
failure of more or less long duration at a patient who
was reanimated.
Incidents
There
are many other accidents, definitely less serious: -
accidents of intubation trachéale : it can
be a broken tooth, or a lesion of a vocal cord; -
the ulcer of cornea : caused by the adhesive
plaster which one sticks on the eyelids to keep them
closed; - compressions of the nervous trunks
: the position of the patient on the operating table
involves sometimes compressions of the nerves, in particular
on the level of the arms and leg, likely to be later
on at the origin of driving or sensitive paralyses;
- burns : they are caused by the electric
lancet.
During
the alarm clock
They
are the most frequent accidents, this is why the alarm
clock is the period which must be supervised best. This
stage, indeed, one observes a "recirculation" of the
anaesthetic drugs. After the apparent alarm clock of
the patient, drugs still present in the organization
can involve its rendormissement. This is why it is important
to have at disposal a recovery room equipped well in
material and a personnel. The recovery room is not obligatory,
but it is recommended that each hospital has one of
them.
This
nondesired drowsiness is accompanied sometimes by a
hypoventilation, even of a respiratory stop. It is not
serious when the patient is under monitoring, and it
is even rather frequent.
On
the other hand, this episode can be serious when the
patient is in his room.
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