Prevention of venous thromboembolism: improving practice in surgical patients.

AIMS: Venous thromboembolism (VTE) is the most common preventable cause of hospital-related mortality. There are major inadequacies internationally in administering appropriate prophylaxis. Our initial aim was to show whether our local effectiveness of administration was equally poor. With local inadequacy confirmed, our second aim was to design, implement and evaluate the efficacy of a new VTE protocol nested within a surgical clerking proforma. METHODS: A pilot audit of the prescription and administration of enoxaparin and thromboembolic deterrent stockings for VTE prophylaxis in 51 acutely admitted surgical inpatients (Round 1) was performed against local guidelines derived from the American College of Chest Physicians (ACCP) criteria. The authors then designed and implemented a VTE prevention protocol incorporating risk assessment and decision support within a new clerking proforma for acute surgical admissions. Local practice was audited against the same criteria in Round 2, which comprised 60 consecutive acute surgical admissions in the same district general hospital. RESULTS: In the pilot study, only (19/51) 37% of subjects received appropriate VTE prophylaxis. Over half of patients were at high risk for VTE; 18/29 high risk patients and 4/10 medium risk patients were not adequately protected. Following implementation of the quality improvement intervention, (53/60) 88% of subjects received appropriate prophylaxis (p<0.001). CONCLUSIONS: Implementation of a VTE protocol as part of a clerking proforma for acute surgical admissions is a simple and effective way of ensuring that surgical patients receive appropriate thromboprophylaxis. A similar strategy could be employed to broaden the scope of the National Institute of Clinical Excellence (NICE) guidelines to address VTE prevention in all hospitalised patients.

A comparison between the short term and long term benefits of screening for abdominal aortic aneurysms from the Huntingdon Aneurysm screening programme.

BACKGROUND: The UK Multicentre Aneurysm Screening Study (MASS) showed a 44% reduction in AAA-related mortality after 4 years and predicted an increased number of deaths prevented in the longer term. We aim to compare the 5 and 13 years benefit from aneurysm screening in the Huntingdon Aneurysm screening programme. METHODS: Incidence and mortality of ruptured AAA (RAAA) after 5 and 13 years of screening in a population based aneurysm screening program. RESULTS: Five years of screening resulted in a reduction in the incidence of RAAA of 49% (95% CI: 3-74%). Nine out of 11 ruptures in the invited group did not survive (mortality 82%; 95% CI: 48-98%) compared to 38 non-survivors from 51 ruptures in the control group (mortality 75%; 95% CI: 60-86%). Five years of screening resulted in an RAAA-related mortality reduction of 45% (95% CI: -15 to 74%). After 13 years of screening the incidence of RAAA was reduced by 73% (95% CI: 58-82%). Twenty-one out of 29 ruptures in the invited group did not survive (mortality 72%; 95% CI: 53-87%) compared to 64 non-survivors from 82 ruptures in the control group (mortality 78%; 95% CI: 68-86%). Thirteen years screening resulted in a reduction of mortality from RAAA of 75% (95% CI: 58-84%). The number needed to screen to prevent one death reduced from 1380 after 5 years to 505 after 13 years. The number of elective AAA operations needed to prevent one death reduced from 6 after 5 years to 4 after 13 years. CONCLUSION: AAA screening becomes increasingly beneficial as screening continues over the longer term. Benefits continue to increase after screening has ceased.

ACE inhibitors increase type III collagen synthesis: a potential explanation for reduction in acute vascular events by ACE inhibitors.

INTRODUCTION: Large trials have shown that angiotensin converting enzyme inhibitor (ACE-I) therapy reduces the risk of myocardial infarction and stroke. Acute vascular events are thought to be initiated by plaque rupture. Animal models of atherosclerosis show an increase in extra cellular matrix when given ACE-I therapy. ACE-I therapy could influence collagen synthesis, one of the major constituents of the atherosclerotic cap. METHODS: A nested case-control study was performed within the Huntingdon Aneurysm Screening Project. Subjects were assessed for arterial disease, drug history and smoking. Blood samples were taken for a measure of collagen synthesis, the amino-terminal propeptide of type III procollagen (PIIINP), lipid levels, iron metabolism and cotinine levels. RESULTS: Information was available for 420 subjects. Thirty-five were taking ACE-I therapy and 385 were not. Mean serum PIIINP level was 3.5 microg/l (sd 1.3 microg/l, range: 1.7-16.5 microg/l. There was a marked increase in mean collagen turnover between subjects taking ACE-I therapy compared to those not. Mean PIIINP level for cases and controls was 4.26 microg/l (95% CI: 3.73-4.79 microg/l) versus 3.61 microg/l (95% CI: 3.48-3.75 microg/l). No differences were found for patients taking other antihypertensive drugs. After adjusting for age, weight, height, lipid levels and ferritin, PIIINP levels remained significantly higher in cases than controls: 4.14 microg/l (95% CI: 3.72-4.57 microg/l) versus 3.62 microg/l (95% CI: 3.49-3.75 microg/l) (P-value 0.02). DISCUSSION: These results suggest that ACE-I therapy up-regulates collagen synthesis, and could improve plaque stabilisation. This may provide an explanation for the decrease in acute vascular events observed in patients on ACE-I therapy.

LDL cholesterol is associated with small abdominal aortic aneurysms.

OBJECTIVE: To examine the relationship between serum lipids and abdominal aortic aneurysms (AAA). METHODS: Two hundred and six males (>50 years) with AAA (> or =30 mm) detected in a population based screening programme were compared with 252 age-matched male controls in a nested case-control study. Smoking status, previous medical and family histories, height, weight, blood pressure, ankle brachial pressure index (ABPI) and non-fasting lipid profile were recorded. RESULTS: Cases were found to have significantly higher LDL cholesterol than controls. LDL cholesterol was an independent predictor of the risk for aneurysms in a logistic regression model adjusting for smoking status, family history of AAA, history of ischaemic heart disease, presence of peripheral vascular disease, use of lipid lowering medication and treatment for hypertension. There was a linear effect with increased levels of LDL cholesterol increasing the risk of having a small aneurysm (test for trend p=0.03). CONCLUSION: The highly significant association between LDL cholesterol and small aneurysms suggests that LDL, possibly acting via inflammatory mediated matrix degeneration, could be an initiating factor in the development of AAA. The ability of statin therapy to prevent AAA formation requires further investigation.

A cost analysis of surgery for ruptured abdominal aortic aneurysm.

OBJECTIVE: This study compares our costs of salvaging patients with ruptured abdominal aortic aneurysms (AAA) with the costs for unruptured AAAs. METHODS: Details of all AAAs presenting over 18 months were obtained. Costs of repair were carefully calculated for each case and were based upon ITU and ward stay and the use of theatre, radiology and pathology services. We compared the costs in unruptured AAAs with both uncomplicated ruptures and ruptures with one or more system failure. RESULTS: The mortality rate for ruptures undergoing repair was 18% and for elective repairs was 1.6%. The median cost for uncomplicated ruptures was 6427 Pounds (range 2012-13,756 Pounds). For 12 complicated ruptures, it was 20,075 Pounds (range 13,864-166,446 Pounds), and for 63 unruptured AAAs, was 4762 Pounds (range 2925-47,499 Pounds). CONCLUSION: Relatively low operative mortality rates for ruptured AAA repair can be achieved but this comes at substantial cost. On average, a ruptured AAA requiring system support costs four times as much as an elective repair.

Effectiveness and cost of screening for abdominal aortic aneurysm: results of a population screening program.

OBJECTIVES: We undertook this study to calculate the cost per life-year gained in the first round of a screening program for abdominal aortic aneurysm (AAA) and to estimate the costs in a subsequent round. METHODS: This was an intervention study, with follow-up for ruptured aneurysms. Men older than 50 years were screened for asymptomatic AAA. Outcome measures included cost per life-year saved and number of men needed to be screened to save one life. RESULTS: The incidence of ruptured AAA was 2.6 per 10,000 person- years in the screening group and 7.1 per 10,000 person-years in the control group. Screening is estimated to have prevented 10.8 ruptured AAA and 8 deaths per year, gaining 51 life-years per year for the study population, and to have reduced the incidence of ruptured AAA by 64% (95% CI, 42%-77%). Each life-year gained during the first screening round cost $1107. To save one life, 1000 men need to be screened and 5 elective operations performed. We predict that a second round of screening can be cost neutral. CONCLUSIONS: The cost-effectiveness of screening for AAA compares favorably with screening programs for other disorders in adults.

Accuracy of serial screening for abdominal aortic aneurysms by ultrasound.

OBJECTIVES: To assess the accuracy of screening for abdominal aortic aneurysms (AAAs) by ultrasound (US). SETTING: An aneurysm screening programme in Huntingdon. METHODS: False negative tests were identified by tracing all patients with a ruptured aneurysm who were screened and then finding the number classified as normal on US. False positive tests were identified by calculating the number of aneurysmal aortas on US that were classified as normal on CT. Measurement variability of the infrarenal aortic diameter between US and CT was estimated. RESULTS: 14 out of 93 patients with a ruptured AAA since 1991 had been screened. No ruptured aneurysm had been classified as normal on US. All 64 patients with an AAA larger than 4.5 cm on US had their aneurysm confirmed on CT. The mean difference between CT and US measurements was 4 mm. The limit of variability between CT and US was 12 mm. CONCLUSION: No false negative scans were found using a cut off point of 3 cm as abnormal. No false positives were found if subjects with an AAA exceeding 4.5 cm were referred for further procedures. A serial US screening policy has excellent screening performance, justifying its use as a screening tool.

The incidence of small abdominal aortic aneurysms and the change in normal infrarenal aortic diameter: implications for screening.

AIM: to study the incidence of small abdominal aortic aneurysms (AAA), and to investigate what proportion of normal infrarenal aortic diameters (IAD) expand with age. METHODS: longitudinal follow-up in a population-based aneurysm screening programme. The infrarenal aortic diameter (IAD) was measured by ultrasound. A second scan was performed in subjects with a normal aorta after an average of 5.5 years. RESULTS: data were analysed from 4072 subjects, 464 with a small AAA and 3608 with a normal aorta. The infrarenal aorta expanded in 15% of subjects, but significant growth (>5 mm) occurred in only 7%. Age and initial diameter were independent predictors for aortic dilatation. The effect of diameter at first screen was non-linear. The relative risk for expansion increased dramatically for IADs over 2.5 cm (test for departure of trend: chi2=52, p<0.0001). The effect of age was also non-linear, the risk of expansion was highest in the 60-69 year old age group; test for departure of trend (chi2=13, p=0.002). The incidence of new aneurysms was 3.5 per 1000 person-years (py) (95% CI: 2.8-4.4). The highest incidence of new aneurysms was found in the 60 to 69 year old age group. CONCLUSION: only a small proportion of the population is prone to aortic dilatation. Patients over 70 with an IAD <2.5 cm can be discharged from follow-up.

The association between connective tissue laxity and the risk of an abdominal aortic aneurysm.

AIMS: to investigate whether connective tissue laxity is associated with abdominal aortic aneurysms (AAA). METHODS: a nested case control study in a population-based screening programme. The presence of pes planus, scoliosis, pectus deformities, flexible auricular cartilages and Gorling's sign were combined with the Beighton joint mobility score to form a connective tissue laxity score. The association between connective tissue laxity and the risk of AAA was investigated through a logistic regression model. Type III collagen turnover was assessed using a serum radio-immunoassay for type III procollagen (PIIINP). RESULTS: data from 231 controls (aortic diameter <2.5 cm) and 190 cases (AAA >2.9 cm) were analysed. Odds ratios (OR), adjusted for known confounders were 3.1 (95% CI: 1. 1-8.6) for the highest group of connective tissue scores and 2.4 (95% CI: 1.0-5.4) for the middle group, compared with those with no signs of abnormal connective tissue function. There was no difference in mean collagen turnover between cases and controls, nor between those with a stable AAA >4 cm and those with an expanding AAA. CONCLUSION: connective tissue laxity is associated with a higher risk of having an AAA. The collagen turnover is similar in subjects with an AAA and controls. Aneurysms may be associated with abnormal connective tissue rather than an increased breakdown of normal collagen.

Wave optics simulation of atmospheric turbulence and reflective speckle effects in CO2 lidar.

Laser speckle can influence lidar measurements from a diffuse hard target. Atmospheric optical turbulence will also affect the lidar return signal. We present a numerical simulation that models the propagation of a lidar beam and accounts for both reflective speckle and atmospheric turbulence effects. Our simulation is based on implementing a Huygens-Fresnel approximation to laser propagation. A series of phase screens, with the appropriate atmospheric statistical characteristics, are used to simulate the effect of atmospheric turbulence. A single random phase screen is used to simulate scattering of the entire beam from a rough surface. We compare the output of our numerical model with separate CO(2) lidar measurements of atmospheric turbulence and reflective speckle. We also compare the output of our model with separate analytical predictions for atmospheric turbulence and reflective speckle. Good agreement was found between the model and the experimental data. Good agreement was also found with analytical predictions. Finally, we present results of a simulation of the combined effects on a finite-aperture lidar system that are qualitatively consistent with previous experimental observations of increasing rms noise with increasing turbulence level.

The association between cigarette smoking and abdominal aortic aneurysms.

PURPOSE: The purpose of this study was to investigate the precise effect of smoking, duration of smoking, and cessation of smoking on the risk of the development of an abdominal aortic aneurysm (AAA). METHODS: A nested case control study was carried out in a population-based screening program for men over the age of 50 years. Smoking data were collected by questionnaire, and serum levels of cotinine were used as an objective measure of nicotine exposure. RESULTS: Data of 210 cases and 237 control individuals were analyzed. Current smokers were 7.6 times more likely to have an AAA than nonsmokers (95% confidence interval, 3.3%-17.8%). Exsmokers were 3.0 times more likely to have an AAA than nonsmokers (95% confidence interval, 1.4%-6.4%). Duration of smoking was significantly associated with an increased risk of AAA, and there was a clear linear dose response relationship with the duration of smoking; each year of smoking increased the relative risk of AAA by 4% (95% confidence interval, 2%-5%). In contrast, the effect of the amount smoked disappeared when an adjustment was made for the duration of smoking. After the cessation of smoking, there was a very slow decline in the risk of the occurrence of an AAA. Smoking was associated with a higher relative risk of a small aneurysm than a large aneurysm. Serum cotinine levels were higher in men with a small aneurysm than in men with a large aneurysm. Cotinine levels were similar in expanding aneurysms and stable aneurysms. CONCLUSION: The duration of exposure rather than the level of exposure appears to determine the risk of the development of an AAA in men older than 50 years. The slow decline of risk after the cessation of smoking and the higher relative risk for small compared with large aneurysms suggest that smoking is an initiating event for the condition.

The influence of screening on the incidence of ruptured abdominal aortic aneurysms.

PURPOSE: The purpose of this study was to estimate the influence of a screening program on the incidence and mortality of ruptured abdominal aortic aneurysms (RAAAs). METHODS: The effects of screening on the incidence and death rate of RAAAs were investigated with a stepped wedge study design. RAAAs that occurred in the Huntingdon district were traced with an examination of all hospital records and community postmortem records. RESULTS: During the 5-year period from 1991 to 1996, 78 RAAAs occurred in the Huntingdon district: 62 in men and 16 in women. Eleven of the 62 men with RAAAs had been invited for screening. The incidence of RAAA in the invited group was 3.7 per 10,000 person-years (py; 95% confidence interval [CI], 1.5 - 7.3). In the noninvited group, the incidence was 7.3 per 10,000 py (95% CI, 5.3. - 9.2), a rate ratio of 0.51 (95% CI, 0.26 - 0.97). The mortality of rAAAs in the invited group was 3.0 per 10, 000 py (95% CI, 1.4 - 5.4) as compared with 5.4 per 10,000 py in the noninvited group (95% CI, 3.9 - 7.3), resulting in a rate ratio of 0. 55 (95% CI, 0.26 - 1.15). CONCLUSION: Screening for asymptomatic AAAs can reduce the incidence rate of RAAAs by 49% (95% CI, 3% - 74%).

Incidence among men of asymptomatic abdominal aortic aneurysms: estimates from 500 screen detected cases.

OBJECTIVES: To determine the incidence of asymptomatic abdominal aortic aneurysms and the implications for an ultrasound screening programme in England and Wales. METHODS: First screen data were obtained from the Chichester and Huntingdon screening studies and used to estimate the prevalence of abdominal aortic aneurysms. The incidence of new, asymptomatic aneurysms was estimated from the prevalence rates observed in the Huntingdon screening study. SETTING: Screening programmes in Huntingdon and Chichester using ultrasound to screen all men over the age of 50 and men over age 65 respectively. RESULTS: The prevalence of abdominal aortic aneurysms ranged between 5.32% and 8.02% and between 6.18% and 9.88% of men aged between 65 and 79 in Chichester and Huntingdon respectively. Annual incidence rates, estimated by age, rose steadily reaching a peak of 0.67% of the Huntingdon population per year at age 65. Thereafter incidence falls. Estimates of the incidence of new asymptomatic abdominal aortic aneurysms, based on the observed prevalence data, were calculated and showed a peak at age 65. CONCLUSIONS: Hypotheses are offered to explain this unexpected early peak in incidence. This information should allow the definition of the optimum age for screening, and the relative benefits of screening at different intervals if widespread screening is adopted in the future.

Ruptured abdominal aortic aneurysm in the Huntingdon district: a 10-year experience.

A study was undertaken to establish the true incidence of ruptured abdominal aortic aneurysms (RAAA) in the Huntingdon districts. RAAAs in the Huntingdon district between 1986 and 1995 were studied retrospectively. Data were collected from hospital records and hospital and community autopsies. There was a total of 139 cases of RAAA; 119 were males and 20 females, giving a M:F ratio of 6:1. The incidence of RAAAs was 17.8/100,000 person years (py) in males and 3.0/100,000 py in females. Mean age at rupture was 75.5 years in men (95% confidence intervals (CI) 74-78 years) and 80.2 in women (95% CI 78.8-83 years). There was an age-specific increase in incidence after the age of 65 years in men and after 80 years in women, although 12.6% of all RAAAs occurred in men under 65 years. In all, 100 patients were confirmed to have died of RAAA during the 10-year period. This represents 79% of all ruptures discovered. Almost three-quarters of patients did not reach the operating theatre. Of the 61 patients operated on, 29 survived (48%). The size of the aneurysm at rupture was recorded in 68 cases (49%). The mean size was 8.14 cm (SD 2.0 cm). In five cases (7.4%), rupture occurred in AAAs smaller than 6 cm. The overall mortality from RAAA in Huntingdon health district is approximately 80% and three-quarters of all deaths occurred without an operation.

The infrarenal aortic diameter in relation to age: only part of the population in older age groups shows an increase.

OBJECTIVES: To resolve whether the infrarenal aortic diameter (IAD) continues to increase throughout life; to ascertain the relationship between IAD and age, sex, body size, and smoking status, and to determine whether these factors influence the IAD over the entire range of aortic diameters or only in a proportion. SETTING: Combined cross-sectional data from two population-based screening programmes for abdominal aortic aneurysms (AAA) in Huntingdon (U.K.) and Rotterdam (The Netherlands). METHODS: The antero-posterior diameter of the infrarenal aorta was measured. The influences of age, gender, body size and smoking status were examined. RESULTS: Data were analysed from 3066 women and 8270 men. In men, mean IAD rose from 20.7 mm to 23.5 mm in the older age groups. However, IADs remained constant below the 75th perentile in men and the 85th percentile in women. Similarly only the top 15-25% of the aortic diameters were larger in smokers compared with non-smokers. CONCLUSIONS: The aortic diameter increased with age in only a minority of the population. Furthermore, known risk factors for AAA contributed to aortic dilatation in only the upper tail of the frequency distribution. Thus only 25% of men and 15% of women may be prone to aortic dilatation.

Epidemiology and potential for prevention of abdominal aortic aneurysm.

BACKGROUND: Ruptured abdominal aortic aneurysm (AAA) is a common cause of death which is preventable by elective repair of an asymptomatic AAA. METHODS: The literature was reviewed with emphasis on epidemiological studies and population-based screening surveys. RESULTS AND CONCLUSION: The prevalence of small AAA ranges between 3 and 8 per cent. The incidence of asymptomatic AAA seems to be increasing, although exact incidence estimates vary. The most important risk factors for AAA are male sex, age, family history and smoking. Hypertension is associated with a mildly increased risk, but diabetes is not associated with any increase. Primary prevention of AAA is not a realistic option. There is no evidence of an effective medical treatment to prevent growth of small AAAs, although trials with propranolol are under way. The only intervention to prevent death from aneurysm is elective repair of the asymptomatic lesion. Screening for asymptomatic AAA can reduce the incidence of rupture. However, further studies are needed to determine the cost effectiveness of screening compared with that of other health programmes.

Growth rates and risk of rupture of abdominal aortic aneurysms.

BACKGROUND: Early identification of abdominal aortic aneurysms (AAAs) may reduce the risk of death from rupture by providing the opportunity for elective repair. Before a screening policy for AAA is implemented, the growth rates of AAAs and the accompanying risk of rupture without intervention should be established. METHODS: The growth rates of AAAs were calculated using longitudinal aneurysmal growth data from screening studies in Chichester and Huntingdon. Estimates of the growth rates of AAAs and the risks of rupture over time were made taking measurement error and individual variability into account. RESULTS: Growth rate estimates were found to vary by initial aortic diameter, with a more rapid growth seen in large aneurysms (50 mm or more). The rate of aneurysm growth did not differ with age or sex. The estimated risk of rupture of an AAA with an initial diameter of 45 mm did not exceed 20-5 per cent over 5 years. An AAA with an initial diameter of 30 mm has a 4.0 per cent or less chance of rupture over 5 years. CONCLUSION: The study provides a more accurate assessment of the risk of aneurysm rupture without surgery and helps to define rescreening intervals for those with an enlarged aortic diameter.

Midline extraperitoneal approach for elective abdominal aortic aneurysm repair.

The incidence of abdominal aortic aneurysms (AAA) is rising and elective repair is becoming more commonplace. We describe a new, simple midline extraperitoneal approach for AAA repair. It is particularly suitable for patients who have an inflammatory AAA, abdominal adhesions or a horseshoe kidney. This approach provides excellent exposure to the whole aortoiliac system without the need for separate incisions, whilst retaining the potential advantages of the extraperitoneal approach.