Epidural analgesia. Observations on physiological and therapeutic aspects of lumbar epidural analgesia in surgery, gynaecology and obstetrics

Moir, Donald Dundas (1969) Epidural analgesia. Observations on physiological and therapeutic aspects of lumbar epidural analgesia in surgery, gynaecology and obstetrics. MD thesis, University of Glasgow.

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Abstract

There are two distinct sections in this thesis. The first concerns original investigations into the effects of epidural analgesia on pulmonary ventilation and acid-base balance. The second section comprises original investigations into various aspects of epidural analgesia in gynaecology and Obstetrics. There are also descriptions of the techniques used, the complications encountered and a short history of epidural analgesia. The effects of epidural analgesia on pulmonary ventilation and acid-base balance Rooting and maximal ventilation were assessed by measuring tidal volume, minute volume, vital capacity and peak expiratory flow rate. Measurements wore made before and during high epidural block in unpremeditated subjects, come of whom were from of respiratory disease and some of whom had chronic broncho-pulmonary disease. Tidal and minute volumes were unaffected by epidural analgesia and vital capacity and peak expiratory flow rate wore only slightly reduced, indicating that paralysis of the respiratory muscles was minimal. The results are analysed statistically. During lower abdominal surgery under epidural analgesia, tidal and minute volumes varied widely in conscious patients, but were always adequate for resting requirements. In the postoperative period resting ventilation was normal and maximal ventilation was about 80 per cent of the pro-operative level during epidural analgesia. This finding demonstrates the superiority of epidural analgesia over other types of post-operative pain relief. Opiate drugs reduce maximal ventilation to about 30 per cent of normal. Acid-base studies by the micro-method of Astrup confirmed the adequacy of resting alveolar ventilation during high epidural analgesia and may be regarded as complimentary to the studios of pulmonary ventilation. The clinical applications of epidural analgesia in patients with severe respiratory disease are discussed and are illustrated by examples from the writer's experience. The mode of action of epidural analgesia is discussed and the method is contrasted favourably with subarachnoid analgesia and general anaesthesia with particular reference to pulmonary function and blood gas values. Epidural analgesia in gynaecology and obstetrics The influence of epidural analgesia on blood loss in gynaecological and obstetric operations was studied. A haemoglobin extraction-dilution technique was used for the accurate measurement of total external blood loss. At 117 Manchester operations and 94 vaginal hysterectomies, when epidural analgesia was administered the blood loss averaged 87 ml. and 166 ml. respectively and was approximately one third of the lose recorded under general anaesthesia, with nitrous oxide and halothane or with nitrous oxide, a muscle relaxant and intermittent positive pi sure ventilation. A statistical analysis shows that profound hypotension is not necessary for the effective reduction of bleeding when epidural analgesia is employed. At forceps delivery, epidural analgesia was associated with a moan blood loss of 274 ml. while pudendal nerve block and general anaesthesia wore associated with losses of 412 ml. and 518 ml. respectively. Statistical analysis of 214 forceps deliveries showed that the anaesthetic technique was the only factor which significantly influenced blood lees after normal labour. In attempt to elucidate the mechanisms by which epidural block reduces operative bleeding, even in the absence of significant arterial hypotension, some studies of the peripheral circulation were performed. It was demonstrated that the central and peripheral venous pressure are reduced by epidural block and it is postulated that the fall in venous pressure contributes substantially to the reduction in blood loss at operation by reducing venous oozing. A heat clearance technique was used to measure peripheral blood flow in the skin and muscle of the lower limb. Epidural analgesia caused a substantial increase in cutaneous blood flow and a email reduction in muscle blood flow. The vascular resistance was reduced in skin and increased in muscle. Allowances wore made for reductions in mean arterial blood pressure. Continuous lumbar epidural analgesia was used in the management of 224 patients who had prolonged and painful labours due to incoordinate uterine action. The factors associated with incoordinate labour are analysed in detail and the high incidence of relative cephalo-pelvic disproportion is stressed. Graphic analysis of 150 labours demonstrated that the cervix usually dilates more rapidly after the induction of epidural analgesia. It appears that epidural block has a therapeutic action on the dysfunctional uterus, as well as providing complete relief of pain and distress. A guardring tocoamometer was used to demonstrate the incoordinate nature of the uterine action. It is probable that the use of epidural analgesia can often safely avoid delivery by Caesarean section in incoordinate labour. The perinatal mortality was 1.3 per cent in this series and is low for oases of this type. Continuous epidural analgesia had a beneficial effect on severe hypertension during labour. The technique is excellent for forceps delivery and, in experienced hands, can be safer than general anaesthesia. The principal hazard of epidural analgesia in obstetrics is an excessive fall in maternal blood pressure which may cause inadequacy of the utero-placental blood flow and foetal hypoxia.

Item Type: Thesis (MD)
Qualification Level: Doctoral
Keywords: Medicine, Pharmacology
Date of Award: 1969
Depositing User: Enlighten Team
Unique ID: glathesis:1969-72737
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06
URI: http://theses.gla.ac.uk/id/eprint/72737

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