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Introduction to the anaesthesia
Types of the anaesthesia
Drugs of the general anaesthesia
Accidents and incidents 


  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.


  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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