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Title: Studies on skin blood flow measurement, with particular reference to amputation level selection
Author: Welch, George Hunter
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1986
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In the United Kingdom over 75% of lower limb amputations are performed as a consequence of ischaemia, and in excess of 80% of these patients are over the age of 60 years. Unfortunately, failure of amputation healing is a common problem,because of the nature of the underlying disease process, and the surgeon's endeavour to perform the amputation at the most distal level possible. Primary amputation failure has disastrous consequences; mortality is increased following revision; subsequent independent mobility is jeapordised; hospitalisation is prolonged with adverse effects on the well-being of the patient and in addition there are the financial implications of decreased efficiency in terms of hospital bed usage. Because of acknowledged difficulties in the selection of the correct amputation level using clinical criteria, a variety of laboratory techniques to supplement clinical examination have been devised. The number of techniques available however is a confusing testimony to the inadequacy of these methods, for to date none has provided an accurate means of pre-operative prediction of the chances of healing at a given amputation level. In Chapter 2 the development of philosophies for selection of amputation level, and the current methods for assessing blood flow are discussed. In particular, the problems which one encounters when attempting to adapt such methods into clinical practice are highlighted. Chapter 3 describes a retrospective analysis of 171 patients with peripheral vascular disease requiring amputation. Two hundred and twenty five amputations were studied with respect to wound healing. Factors such as previous vascular surgery, age, and diabetes mellitus, and their influence on healing were evaluated. The overall healing rate for all amputations was 66%. Although the optimal healing rate (78%) was achieved following above knee amputation, this was at the expense of a high mortality (14%). For foot amputation the primary healing rate was only 51%. The mean hospital stay was 45 days (range 2 - 180) which was a direct result of a combination of poor healing in distal amputations, and difficulties with mobilisation, and subsequent disposal in patients with proximal amputations. The long term survival was extremely limited with a cumulative survival of only 27% after 3 years. This retrospective analysis thus established the need for an objective method to select the appropriate amputation level in these patients. Part II of this thesis is concerned with the method used for the measurement of skin blood flow (SBF). In Chapter 4 the methodology for the measurement of SBF blood flow in this study, based on the clearance of an intradermal deposit of 125-I-iodoantipyrine is described. In Chapter 5 studies on the methodology proved isotope clearance to be flow dependent and reproducible. Part III of the thesis examines SBF in a number of clinical situations. In Chapter 6 the correlation between 125-I-iodoantipyrine clearance and various clinical and laboratory parameters currently used to assess the degree of vascular disease present is investigated, and found to be poor, basically because SBF is a dynamic measurement, in comparison to clinical examination, Doppler blood pressure measurement, and arteriography, all of which are capable of providing limited information only. In Chapter 7 the technique of 125-I-iodoantipyrine clearance is employed to assess the response of patients following surgery aimed at improving distal blood flow. Direct arterial reconstruction caused a significant increase in SBF, but these changes were not apparent following lumbar sympathectomy (Chapter 8). The validity of sympathectomy as a procedure to increase nutritional blood flow in the foot of patients with severe peripheral vascular disease is questioned, and may explain the variable clinical response following sympathectomy in clinical practice. Part IV of the thesis describes the use of the isotope method to select the appropriate level of amputation in patients with end stage peripheral vascular disease. In Chapter 9 a clinical study to assess the relationship of Doppler ankle blood pressure (DABP) and the healing of amputations in the foot is presented. There was no difference in mean DABP in healing (DABP = 89 +/- 8 mmHg) and non-healing (DABP = 91 +/- 12 mmHg) groups. This observation was independent of the presence of diabetes. Pre-operative infection did not influence amputation failure, although sepsis was often a factor responsible for non-healing. Amputation failure was observed in the ranges of Doppler pressure which have previously been considered to be compatible with healing, and the converse, healing at levels considered incompatible was also observed. DABP is not sufficiently reliable for the identification of patients for forefoot amputation. In Chapter 10 a prospective study of the relationship of pre-operative SBF and amputation healing is described. Eighty patients were included in the study. The selection of amputation level was made purely on clinical grounds. When the healing at all levels of amputation was considered, primary healing was achieved in 65% with amputation failure in 23%. There was a significant difference in pre-operative skin blood flow between healing (12.1 +/- 0.6 ml/100g/min), and non-healing (5.8 +/- 1.0 ml/100g/min) groups, but it was not possible to define a precise value to discriminate between healing and non-healing. This was principally due to the inclusion of amputations at the below knee level where healing ocurred at low flows after prolonged periods. However when the patients with foot amputations were selected, a value for SBF of 7 ml/100g/min emerged as the critical flow for healing. At SBF values below this level, failure was inevitable, primarily because of the combination of ischaemia and sepsis. In general therefore, it is concluded that a need exists for a means of accurate pre-operative selection of the appropriate amputation level. The use of 125-I-iodoantipyrine clearance appears to be a simple and reproducible means of measuring skin blood flow. Although there is a significant difference in skin blood flow between healing and non healing amputations, it is only in the forefoot that skin blood flow measurement is capable of providing a value which appears to be critical for healing. With this technique available the identification of patients suitable for conservative foot amputation should be possible, allowing mobility without the use of a prosthesis. It should now be possible to reduce failure of forefoot amputations, and so reduce the hospital occupancy of these patients, free bed use for other categories of patients with peripheral vascular disease, and partially reduce the economic burden that these patients impose on the Health Service.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available