Local anesthetic

A local anesthetic is a Médicament which inhibits in a reversible way the propagation of the signals along the Nerf S. If it is used on the level of specific nervous ways, it is likely to produce effects the such Analgésie (reduction of the feeling of Douleur) and the Paralysie (loss of power of the Muscle).

synthetic local anesthetics are structurally related to Cocaine. They differ from cocaine mainly in that they cuts No deceives potential and C not act one the Sympathoadrenergic system, i.e they C not produce Hypertension local gold Vasoconstriction. -->

The anesthetic buildings differ between them as for their properties pharmacological.
They are used in various techniques of Local anesthesia such:

anesthesia topics (surface)
infiltration
plexus block
epidural blocking (extradural)
anesthesia spinale

Local anesthesias by infiltration: para-apical; intraseptales; intradiploïques; intraligamentaires; intrapulpaires.

The Lidocaïne, a local anesthetic, is also used like Antiarythmique.

Anesthetic of surface by contact

Cocaine

Advantages

not very powerful vasoconstrictor

Disadvantages

high toxicity
allergy

phenomena of dependence

Lidocaïne

Advantages

nonallergenic
much less toxic than cocaine, concentration 5 to 10%

Disadvantages

fairly powerful
toxic with high amount

Other anesthetic of surface

By refrigeration: Cryoanesthésie
Chloride ethyl. Harmful and flammable,
Fréon 114 is not used any more. Also used for the cold tests

Anesthetic by infiltration

Amino-esters

Procaine.

Advantages: no the pharmacodépendance
Disadvantages: very allergenic vasodilator, very , lasted of short action

Tetracaine

more prolonged Action but nevertheless vasodilator

Aptocaïne.

Utilisée only if porphyrie hepatic where the amino-amides are contra-indicated.

Amino-amides

Lidocaïne.

Advantages: very little vasodilatatrice, not allergisante
Disadvantages: toxic effects by overdose.

Prilocaïne.

Advantage: duration of longer action, fast metabolism
Disadvantage: risk methemoglobinemy (prohibited at the expectant mother, limitation in child of less than 3 months)

Mépivacaïne.

Advantages: very slightly vasoconstrictrice, good tissue diffusion.

Articaïne.

Advantages: the most powerful anesthesia and longest; local anesthetic of choice for the expectant mother because ionized form weak, not very liposoluble, strongly related to the proteins
Disadvantages: a little strong concentration according to some.

Ropivacaïne.

rather recent Molecule presenting many advantages: very weak liposolubility, intrinsically vasoconstrictrice, not very toxic.
To remain careful because little retreat

Other associated components

The Vasoconstricteur S

They increase the duration of action and the effectiveness, decrease the quantity of anesthetic, therefore toxicity. They decrease the bleeding.

The Adrenalin

Acts on the receivers α1 and 2 and β2 (→ vasodilatation). Adrenalin increases the cardiac rhythm and the contractibility of the myocardium. An overdose causes: tachycardia, hypertension and increase in the basal metabolism

The Noradrenalin

Acts on the receivers α1 and 2 but not on the β2. It is less effective than adrenalin, and can be more harmful. It can cause an increase in the blood-pressure, but acts neither on the cardiac contractibility nor on the basal metabolism.

The Corbadrine

10 times less active than the noradrénalibne. Used only associated with the aptocaïne in the event of porphyrie.

Other components

The Disinfectant S

Parabens = para-hydroxy-benzoic: anti-fungic and antimicrobic but very allergenic role, it is thus less and less used.

Antioxydant S

EDTA = acid-ethylene-diamide-tétra-acetic: decrease the reactions of oxidations in the carpules

preserving S

Sulphites: like the métabisulfite of sodium or potassium. This molecule is obligatory if there is of the vasoconstrictor.
water

Mechanism of action at the cellular level

The touched nervous cells are in the center of vigilance located in the mésencéphale at the crossroads of sensitive ways and driving ways. The anesthetic ones act on the receiver of the GABA (acid g-aminobutyric), a neuro-transmitter present in the membranes of the neurons.

Side effects

Central nervous system

A local anesthetic, by definition, cannot penetrate the central nervous system. By accident (intravenous injection instead of local), the strong amounts can cause convulsions.

Cardiovascular system

A local anesthetic, by definition, cannot reach the heart where large vessels. By accident (intravenous injection instead of local), the strong amounts can affect the heart and make decrease the blood pressure.

Over-sensitiveness/Allergy

Methemoglobinemy

Accidents

Diagnosis

Beginning similar to a Malayan vagal.

Turbid minors: Paraesthesia of the lips, the language and the ends; feeling of increasing Anguish, faintness general; Cephalgia S, Logorrhée, Euphoria; eye trouble and auditive: dazzling S, Diplopia, Acouphène S; Giddiness S, confusion, Hallucination S
Turbid major:

Neurological signs (often early): Tremor S muscular, Myoclonie of the face; Somnolence, loss of consciousness, Coma; convulsif state; evolution towards ventilatory distress
Signs cardiocirculatoires: irregular pulse; Hypotension; evolution towards inefficiency or the circulatory stop

Evolution

Usually favorable in a few minutes for the minor disorders.
Without symptomatic treatment, the major disorders evolve to the respiratory and circulatory stop.

Treatments

Prevention of the toxic accidents

To inject the slowly warmed solution and to practice an aspiration to check that the solution is not intravascular.

To abstain from infiltrating inflammatory or infected fabrics.

To supervise the patient during the injection and in the 30 min which follows it in order to detect any sign of alarm precociously; In front of any sign of alarm, to stop the injection and to supervise the three great functions: neurological, respiratory and cardiovascular.

Moreover, the stress must be regarded as a risk factor decreased by the dialog, the behavior, the environment of the buildings… and possibly a premedication.

Action to be taken in front of a toxic accident

Minor accident: to stop the care, to lengthen in décubitus dorsal, sloping position; to check freedom and protection of the higher air routes, to reassure the patient; to supervise the state of consciousness, the functions respiratory and circulatory.

Major accident

To call the services of urgent Medical assistance.

Anesthetic buildings used nowadays

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