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Medical cost savings through stroke prevention from 100 consecutive new carotid duplex scans |
Lavenson G S, Sharma D |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology Duplex ultrasound as the prime means of discovering stroke-potential carotid artery lesions in patients referred by physicians for carotid artery duplex ultrasound.
Type of intervention Diagnosis and primary prevention.
Economic study type Cost-effectiveness analysis.
Study population Patients referred for carotid artery duplex ultrasound.
Setting Hospital. The economic analysis was carried out in the USA.
Dates to which data relate Some of the effectiveness and resource use data related to ultrasound examinations performed in 1991. Some of the effectiveness data (which were also used for costing) were obtained from studies published between 1989 and 1993. The price year was not explicitly specified.
Source of effectiveness data The evidence for the final outcomes was based on a single study and a literature review.
Link between effectiveness and cost data Costing was conducted retrospectively both on the patient sample from the present study (mainly related to the costs of the stroke avoidance programme) and on data from the literature, known facts, and experience of one of the authors (mainly related to the estimation of the costs of strokes prevented).
Study sample Power calculations were not used to determine the sample size. The study sample consisted of 100 consecutive new duplex ultrasound examinations conducted on the last consecutive 100 new patients referred to the office of one of the authors. 48 patients were symptomatic versus 52 who were symptom-free.
Study design This was a case-series study, carried out in a single centre. The duration of the follow-up was 1.5 years. No information was given regarding loss to follow-up. Angiography was used selectively and sparingly in the patients in this study. Patients were admitted on the day of surgery and most were discharged the following morning. Carotid artery vascular laboratory findings had been validated by comparison with angiography in a prior study with a finding of 82% correlation. Decisions regarding surgery were primarily based on duplex ultrasound. Angiograms were only obtained if the duplex ultrasound examination was inconclusive or if total occlusion was suspected. Carotid endarterectomies were performed under local anaesthesia and by one of the authors: the 5-year operative morbidity and mortality rate was 0.8%.
Analysis of effectiveness The analysis of effectiveness was based on treatment completers only. The health outcomes were the number of patients with normal carotid arteries, 30-70% stenosis (who were treated medically, consisting of a low-fat, low-cholesterol diet, antiplatelet medication and appropriate duplex ultrasound follow-up at 6 months or 1 year), and greater than 70% obstruction (who were offered endarterectomy); the number of operations performed; and perioperative and postoperative (follow-up) strokes or death.
Effectiveness results The total number of patients with normal carotid arteries, and who were given no specific management, was 45.
The 28 patients with 30-70% stenosis were treated medically, and the 27 with greater than 70% obstruction were offered carotid endarterectomy. Of this latter group, 25 (8 of whom had bilateral lesions) elected for surgery, resulting in 33 operations (23 symptomatic and 10 symptom-free).
There were no perioperative strokes or deaths and no further strokes occurred during the study follow-up period of 1.5 years in either the surgical or non-surgical groups.
Clinical conclusions It should be noted that, after proper laboratory validation, angiography for confirmation was not employed in the medical arm of the Asymptomatic Carotid Atherosclerosis Study (ACAS) and the present authors also felt that their findings of not significantly diseased carotid arteries were accurate. It should be emphasised that this was not a study of carotid artery screening. All patients were referred by their physicians for specific reasons. 'Symptom-free patients' were referred because of bruits, a contralateral symptomatic lesion, or non-lateralising symptoms, most of which were left or were improved following carotid endarterectomy.
Outcomes assessed in the review The following outcomes were assessed: the percentage of strokes anticipated in unoperated symptomatic and symptom-free patients, proportion of symptom-free patients who would have had transient ischemic attacks or amaurosis fugax and the corresponding rates of anticipated strokes if not operated on, the proportion of severe and moderate strokes in true strokes, mortality rate of patients with severe strokes within 1 month and proportion who require long-term care.
Study designs and other criteria for inclusion in the review No study designs or other criteria were reported in the review.
Sources searched to identify primary studies The sources searched were not reported in the review.
Criteria used to ensure the validity of primary studies The criteria used were not reported in the review.
Methods used to judge relevance and validity, and for extracting data The methods used were not reported in the review.
Number of primary studies included In total, 5 studies were included in the review.
Methods of combining primary studies The method of combination was not reported in the review.
Investigation of differences between primary studies Results of the review The percentage of strokes anticipated in unoperated symptomatic patients with greater than 70% stenosis was 24% within 1.5 years.
The corresponding value for the symptom-free patients (extrapolated to a time period of 1.5 years) was 7.6%.
The proportion of symptom-free patients who would have had transient ischemic attacks or amaurosis fugax was 9%; 24% or 2.25% respectively of these patients would have had strokes if not operated on, for a total stroke prevention of 9.85%.
The proportion of severe and moderate strokes in true strokes was 50% each.
There was a 15% mortality rate of severe strokes within 1 month and 85% required long-term care.
Measure of benefits used in the economic analysis The benefit measure was the number of strokes prevented. The number of duplex ultrasound (DUS) required to prevent one CVA was also reported.
Direct costs Costs were not discounted despite the time frame of 4 years considered for the long-term care of survived patients with strokes. Some quantities (duration of use of different facilities and number of tests) were reported separately from the costs. Cost items were reported separately. Cost analysis covered the costs of stroke avoidance procedures (including the duplex ultrasound examinations, the secondary examinations used selectively (magnetic resonance imaging, transcranial Doppler, technetium nuclear brain scan, angiography, and carotid endarterectomies), and estimated medical care costs of strokes prevented (including hospitalisation, rehabilitation, home care, equipment, and long-term care)). The perspective adopted in the cost analysis appears to have been that of the health care system. The sources of cost data were local Medicare payments, data from the literature, and the experience of one of the authors. The price year was not explicitly specified.
Indirect Costs Indirect costs were not included.
Sensitivity analysis No sensitivity analysis was conducted.
Estimated benefits used in the economic analysis The number of strokes prevented among symptomatic patients with 23 operations was 5.520 (2.76 with moderate cerebrovascular accident (CVA) and 2.76 with severe CVA); among symptom-free patients with 10 operations it was 0.985 (0.493 with moderate CVA and 0.493 with severe CVA): the total was 6.505. The overall number of duplex ultrasound (DUS) required to prevent one CVA was 15.4. The corresponding number of DUS required to prevent one CVA in symptomatic patients was 8.7 and 52.8 for symptom-free patients.
Cost results The overall (n=100) stroke cost avoided was $958,838 versus $300,494 for the cost of stroke avoidance procedure, resulting in overall total cost savings of $658,344.
The stroke cost avoided for the symptomatic patients (n=48) was $813,524 versus $210,418 for the cost of stroke avoidance procedure, resulting in cost savings of $603,106.
The stroke cost avoided for the symptom-free (n=52) was $145,314 versus $90,076 for the cost of stroke avoidance procedure, resulting in cost savings of $55,238.
Synthesis of costs and benefits Costs and benefits were not combined since the intervention (the use of DUS) was the dominant strategy.
Authors' conclusions This study has shown that when a patient is referred by a physician for a duplex ultrasound of the carotid arteries for a reason, this not only leads to the discovery of stroke-potential lesions and, by safely performed carotid endarterectomy, the avoidance of devastating strokes, but in so doing avoids the high medical care costs of the strokes prevented and saves money for the health care system.
CRD COMMENTARY - Selection of comparators The strategy of not performing duplex ultrasound was implicitly regarded as the comparator. This allowed the active value of the intervention to be evaluated.
Validity of estimate of measure of effectiveness The internal validity of the effectiveness results may be open to question, given the retrospective nature of the study design performed in the study institution and the possible limitations of the literature review used to derive some of the effectiveness data (details of which were not given). As a result, it is not possible to objectively assess whether the study sample was representative of the study population.
Validity of estimate of measure of benefit The estimate of the benefit measures was directly derived from the effectiveness analysis. It would have been useful to know why the more widely used benefit measures such as life-years gained or quality-adjusted life-years were not adopted in this study.
Validity of estimate of costs The following features enhanced the validity of the cost results: some quantities were reported separately from the costs; a cost breakdown was given; the perspective adopted in the cost analysis appears to be specified. However, in terms of limitations: the price year was not reported; the cost analysis was conducted retrospectively; it is not entirely clear whether the cost data were true costs or charges/reimbursements; statistical analyses were not performed on resource use and cost data; the effects of alternative procedures on indirect costs were not addressed; the cost results may not be generalisable outside the study setting due to lack of sensitivity analyses.
Other issues Given the inherent limitations of the study design and lack of sensitivity analysis, the study results may need to be treated with some caution. The issue of generalisability to other settings or countries was not addressed although appropriate comparisons were made with other studies. The degree to which the study sample was representative of the study population was not explicitly addressed.
Implications of the study Symptom-free patients are worthy of consideration since it has been estimated that half of the major strokes that occur in this group do so without any warning or lateralising event; hence carotid endarterectomy in this group is seriously recommended by many. More stroke prevention and cost saving would undoubtedly be shown with a longer period of follow-up.
The conclusion of this study is of particular importance with the advent of managed care in which there is concern that patients may not be referred for carotid artery duplex ultrasound, dangerous lesions will not be discovered, and the required carotid endarterectomy will not occur. Consequently, preventable strokes will not be prevented, resulting in adverse health consequences, and higher costs for the medical care system.
Bibliographic details Lavenson G S, Sharma D. Medical cost savings through stroke prevention from 100 consecutive new carotid duplex scans. Cardiovascular Surgery 1996; 4(6): 753-758 Indexing Status Subject indexing assigned by NLM MeSH Carotid Arteries /surgery /ultrasonography; Carotid Stenosis /surgery /ultrasonography; Cerebrovascular Disorders /economics /prevention & Cost Savings; Cost-Benefit Analysis; Endarterectomy, Carotid /economics; Humans; Risk; Ultrasonography, Doppler, Duplex /economics; control AccessionNumber 21997006751 Date bibliographic record published 31/07/2001 Date abstract record published 31/07/2001 |
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