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Title: Epidural analgesia
Author: Scott, D. B.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1959
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The author's experience with epidural analgesia began in 1954. At first the caudal route was chosen until it became apparent that the failure rate was rather high, and toxic reactions to the injected local anaesthetic drug were not infrequent. The lumbar route was then tried and, rather surprisingly, this proved somewhat easier. Failures were fewer, and because a slow unforceful injection could be made (in contradistinction to caudal block), toxic reactions were eliminated. Though self-taught, a reliable technique was soon adopted and epidural analgesia became the method of choice in many types of operation. To date, more than 450 epidural blocks have been performed, including 60 caudal blocks. There are many unsolved problems relating to this type of anaesthesia, and during the five years the writer has been practising it, an attempt has been made to probe into some of them. It will be appreciated that most of these investigations were carried out while supplying a clinical anaesthetic service, often single- handed, to busy surgical units, and this imposed considerable limitations on experimental methods. All the epidural blocks were performed on patients about to undergo surgery, and their interests had to take precedence over experimental investigation. Moreover, surgeons could not be kept waiting indefinitely while observations were carried out. In spite of these limitations, however, the following investigations were undertaken: - (1) A small series of dissections (about 20 in number) of sacral canals was carried out in the dissecting room in order to become familiar with the anatomy, and see if there were any anatomical reasons why caudal block was less reliable than lumbar epidural block. (2) In a series of 100 cases (including 40 caudal blocks) hyaluronidase was added to the anaesthetic solution in an attempt to speed up the onset of analgesia. The results, which are discussed, had in addition a bearing on the site of action of epidurally injected local anaesthetic. (3) Thirty cases were given the new local anaesthetic drug carbocaine, and a comparison with lignocaine was made. (4.) The incidence of hypotension during the course of epidural analgesia was noted, and views are expressed regarding the applicability of this method to controlled hypotension. A comparison is made with hypotension produced by spinal blockade and by ganglionic blocking agents. (5) One of the major advantages of epidural analgesia in the reduction of operative blood loss. Unfortunately, almost all protagonists of various forms of anaesthesia claim this for their own particular method and almost always the claim is unsubstantiated by any evidence, other than clinical impression. In order to get more information on this point, blood loss was estimated by swab weighing on cases of pelvic floor repair (Fothergill's operation). By this method, the blood loss in a series of cases could be calculated reasonably accurately in a standard operative procedure performed under epidural anaesthesia, and this could be compared with a series performed under general anaesthesia. The role of the various factors which may reduce bleeding, such as hypotension, could then be assessed. (6) During the course of the preceding investigation on blood loss and in an effort to find the most satisfactory anaesthetic for pelvic floor repairs, local infiltration of the operative area with dilute (1/200,000) adrenaline was used. While proving satisfactory as a haemostatic agent, the adrenaline had very interesting side -effects. In the conscious subject, adrenaline given in sufficient dosage causes a rise in blood pressure by its stimulating action on the heart, tachycardia occurring at the same time. Its action on peripheral blood vessels is varied, some being constricted while others are dilated. The overall effect 15 is one of vasodilatation (Robson and Keele), so that the rise in blood pressure is solely due to increased cardiac output as a result of direct stimulation of the myocardium. Under anaesthetic conditions, however, the adrenaline would appear to act quite differently. Firstly, the patients seem more sensitive to its action, a marked rise of blood pressure occurring after a relatively small amount of adrenaline is injected. At the same time the pulse rate, instead of being raised, is unaffected. It would seem, then, that dilute adrenaline injected into anaesthetised patients causes marked vasoconstriction with little or no direct action on the myocardium. Details of these investigations and their results are given in the course of this thesis which also includes the writer's experience of the methods of producing epidural analgesia, and the management of patients undergoing this form of anaesthesia.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available