Residential Care of Mentally Handicapped Children
Authors: J. Tizard
Journal: BMJ (1960)

LOCAL ANALGESIC DRUGSSuch solutions are most effective in smaller nerve fibres and can produce a chemical sympathectomy lasting up to a year when injected into the lumbar sympathetic chain.Vasoconstricting Drugs No description of local analgesic drugs can be com- plete withont mention of the vasoconstrictors which are commonly added.The function of these drugs is twofold: to prolong the action of the analgesic drug, thus reducing the rate of absorption, and hence, at the same time, reducing the risk of toxic reactions.In fact, it is a safe rule to add a vasoconstricting agent when injecting any local analgesic which causes vasodilatation.Adrenaline is still the commonest drug used in spite of not infrequent systemic side-effects.These reactions are usually the result of overdosage or inadvertent intravenous injection.Adrenaline is most frequently marketed in a 1 /1,000 solution, and strict observance of 0.5 ml. as the maximum dose (0.5 mg.) will much reduce their incidence.For most purposes a concentra- tion of 1:200,000 is adequate, and even 1:600.000can produce efficient vasoconstriction if given sufficient time to act.Adrenaline is difficult to sterilize and readily decomposes.Thus its addition to a local analgesic solution, unless this is freshly prepared, requires an acid pH, which in turn leads to irritation of tissues and pain on injection.However, the alternatives such as phenylephrine, which is reputed to have little effect on the heart or cerebral cortex, and cobefrin, which produces less vasoconstriction and cannot be autoclaved, have found little favour in Great Britain. Mucolytic EnzymeHyaluronidase is the mucolytic enzyme which breaks down hyaluronic acid and provides a greater area of distribution for injected drugs.When used with local analgesic solutions it provides a more extensive field of analgesia and rapid penetration of nerve fibres.But, since absorption may take place from a larger area, the duration of analgesia is shortened, and the toxicity increased.While having obvious possibilities, this drug should never be used as an excuse for a poor technique and an inadequate knowledge of anatomy. Choice of DrugsProcaine may still be used most commonly, but lignocaine, in spite of a relatively higher cost, is more efficient and convenient for general use, quite apart from being the undoubted drug of choice for extradural analgesia.If vasoconstriction and shrinkage of mucous membranes is required for ear, nose, and throat surgery, cocaine retains pride of place for topical application.But if vasoconstriction is unimportant, lignocaine, ametho- caine, and cinchocaine all have their adherents, who base their preference on a fear of the toxic reactions from cocaine.For spinal analgesia cinchocaine or amethocaine offers a duration of effect adequate for most surgical procedures.Lignocaine would not appear to have any particular advantages in this method of analgesia except in the conduct of a continuous spinal block maintained with serial injections.Whatever the merits or otherwise of spinal analgesia, there is little evidence that any particular drug in use to-day can be blamed for the post-spinal sequelae which have tended to bring the method into disrepute.The limitations of the various drugs available having been accepted, the choice will probably be determined by such practical considerations as expense, convenience, and familiarity.Each drug has its own particular advantages, but an understanding of their properties and limitations will lead to more efficient analgesia and fewer undesirable side-effects.