Basic overview of local anaesthesia

							Basic overview of local anaesthesia

There are many instances where it is preferable to do a procedure under local
anaesthesia. These indications vary from suturing a small wound to major procedures
for respiratory cripples. Local anaesthesia was first demonstrated with cocaine in 1880
by Koller. The clinical use of spinal and extradural anaesthesia was demonstrated a
few years later by Bier and Sicard at the turn of the century.

Local anaesthetic agents are derived from two pharmacological groups, the
aminoesters and aminoamides. These, when applied to a nerve in sufficient
concentration, prevent the conduction of electrical impulses along the nerve membrane.

Their mechanism of action is uncertain but appears to be similar to that of general
anaesthetics in that they seem to interfere with protein ion channels of the nerve
membrane.

Lignocuine hydrochloride

This is an aminoamide local anaesthetic agent. It is probably the most commonly used
local anaesthetic and its pharmacological properties are similar to those of all the other
members within the group. lt is a very stable compound. It is supplied in vials,
ampoules, topical sprays and as a jelly or ointment.

It has a rapid onset of action, but is also fairly well absorbed into the general circulation
and therefore to reduce its systemic effects and prolong its action, it is usually combined
with very small doses of adrenaline.

When absorbed or given systemically lignocaine has effects on the cardiovascular and
central nervous systems. On the central nervous system increasing plasma
concentrations result in tinnitus, light headedness, visual and auditory disturbances,
restlessness and shivering. Increasing the dose will produce generalized convulsions
and eventually coma and death.

The direct action on the heart is to depress the myocardial muscles as well as the
myocardial conducting system. This latter effect is used clinically to treat ventricular
arrhythmias. Lignocaine can be used as a 1%-4% solution depending on the site of
administration. The toxic dose, which is 4 mg/kg without adrenaline and 7 mg/kg with
adrenaline. should never be exceeded: the effect of lignocaine lasts approximately
6(J~9O minutes.

Agitation and confusion are also common post-operative findings. There are many
causes ranging from a full bladder to drugs which have been given. or the psychological
response to the operation. In all instances it is essential to establish a cause and treat it.
This will usually reverse the agitation or confusion. Agitation may also give early
warning of more serious complications, e.g. hypoxaemia, and therefore it should never
be ignored
Abnormal bleeding is due to one of 4 major causes. There may be: (1) a discontinuity or
abnormality of a vessel; (2) reduced clotting factors; (3) reduction in platelets. a
common finding following a large blood transfusion: (4) increased breakdown of the clot
that has been formed. Treatment of any blood disorder is aimed at correcting the cause.
Sometimes (e.g. in disseminated intravascular coagulation) several of the
above-mentioned factors are abnormal.