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.
"Basic overview of local anaesthesia"