- Email: [email protected]
The quality of care for patients with abdominal aortic aneurysms
doi:10.1016/S0967-2109(03)00102-9
Cardiovascular Surgery, Vol. 11, No. 5, pp. 331–336, 2003 2003 The International Society for Cardiovascular Surgery Published by Elsevier Ltd. All rights reserved. 0967-2109/03 $30.00
www.elsevier.com/locate/cardiosur
The quality of care for patients with abdominal aortic aneurysms Justin B. Dimick and Gilbert R. Upchurch Jr. University of Michigan Medical Center, Section of Vascular Surgery, 2210 Taubman Health Care Center, 1500 E. Medical Center Drive, Ann Arbor, MI, 48109-0329, USA Abdominal aortic aneurysm (AAA) repair is a complex surgical procedure and is commonly performed in a variety of practice settings across the United States. The quality of surgical care is neither ideal nor uniform across medical centers with documented variation in both utilization and outcomes. Recent data document that screening, though effective in reducing AAA-related deaths, may have only small contributions to population mortality. Large randomized trials have provided evidence regarding the timing of AAA repair and provide strong evidence for the development of appropriateness criteria. In general, lower mortality rates have been consistently associated with higher provider volume (surgeon and hospital) and specialization in vascular surgery. Current health policy initiatives suggest referral of several complex procedures to high volume centers based on minimum volume standards. Processes of care of high-volume providers and vascular surgeons should be studied and used to guide quality improvement efforts for lower volume providers and surgeons of other specialties performing AAA repair. 2003 The International Society for Cardiovascular Surgery. Published by Elsevier Ltd. All rights reserved. Keywords: abdominal aortic aneurysms, quality of care, screening, detection
Introduction The quality of care for patients with vascular disease varies across medical centers [1–3]. Rates of postoperative complications and operative mortality, for instance, differ widely across hospitals for most highrisk surgical procedures, with some of the largest differences observed for abdominal aortic aneurysm (AAA) repair [1–3]. In the United States, a recent report from the Institute of Medicine (IOM) has highlighted these differences between medical centers [4]. As a result, many stakeholders (e.g. patients and payers) are interested in holding physicians and hospitals accountable for providing high quality health care. Abdominal aortic aneurysms are a common cliniCorrespondence to: G.R. Upchurch. Tel.: +1-734-936-5790; fax: +1734-647-8967; e-mail: [email protected]
CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5
cal problem encountered by a variety of healthcare professionals. The quality of care for patients with the AAAs is potentially related to screening and recognition in at-risk populations, and is certainly dependent upon the appropriate timing of repair and optimal outcomes of the surgical repair. The objective of the current review is to discuss emerging evidence in each of these areas in the context of the quality of care for patients with AAAs. The diffusion of endovascular technology has implications on changes in both utilization and outcomes of AAA repair and these are considered in the discussion. When assessing the quality of care, it is important to maintain a distinction between structure, process, and outcomes of a provider–patient encounter. Structure relates to the material resources, human resources, and organizational structure of a health care organization; process relates to what is done to and for the patient; and outcome is how the process and structure allow patients to achieve desired 331
The quality of care for patients with abdominal aortic aneurysms: Justin B. Dimick and Gilbert R. Upchurch Jr.
changes in health status. Structural attributes associated with improved outcomes after complex aortic surgery include provider experience (hospital or surgeon volume), anesthesia specialists, and intensive care unit physician and nurse staffing. At least in part, organizational structure leads to improved quality through promotion and practice of more effective processes of care. In considering the process of care it is important to recognize three distinct areas, which include the preoperative, intraoperative, and postoperative phases of care. For AAA repair, several health care processes can be linked to improved outcomes during each stage. Examples include the appropriate cardiac and pulmonary evaluation and optimization before the operation (preoperative phase), use of perioperative antibiotics, resuscitation, and surgical technique (intraoperative phase), and invasive monitoring, ongoing resuscitation, and the prompt diagnosis and management of complications (postoperative phase) (Table 1).
Detection and screening The natural history of AAAs is characterized by progressive expansion and eventual rupture. Rupture of an AAA is associated with an extremely high mortality rate. Even patients fortunate enough to make it to the operating room experience a 50% operative mortality rate [2]. Consequently, the objective of surgical replacement of the aorta is to prevent rupture. Screening for AAAs, in theory, should increase the proportion undergoing elective repair and reduce the population-based mortality rate of this disease process. Many AAAs are currently detected either on physical exam (pulsatile abdominal mass) or incidentally on abdominal imaging (e.g. ultrasounds, computed tomography) performed for another reason. Screening in at-risk groups, such as elderly men with hypertension, is recommended but very few largescale organized screening efforts currently exist. The recent publication of the Multicentre Aneurysm Screening Study (MASS) provides good evidence that screening efforts aimed at older men would reduce AAA-related rupture and death [6]. Table 1
This large trial randomized more than 60 000 elderly men (65 to 74 years old) to be invited or not invited to receive ultrasound screening. The majority of men (80%) who were invited volunteered to have screening performed. Those with AAAs were continually followed with ultrasound for a mean of 4.1 years and those with aneurysms greater than 5.5 cm were offered elective repair. As a result, there was a significant reduction in AAA-related deaths (42% relative reduction) in the group who received screening. In a related cost-effectiveness analysis, the authors concluded that the additional cost of the screening program was $98 per person [7]. Over 4 years, the overall cost-effectiveness was found to be $57 700 per quality adjusted life year (QALY). Importantly, after 10 years, the authors concluded that figure would drop to $12 800 per QALY, which is well below the threshold considered to be cost-effective. However, when examining the absolute risk difference between the two groups (0.19 vs. 0.33%) the actual benefits of universal screening appear small. For example, 712 patients (95% CI, 500 to 1000) would have to be screened to prevent one AAArelated death [6]. Thus, until specific groups of patients at higher risk of rupture can be identified, screening for AAA repair should be seen as an acceptable, but not mandatory measure. From a quality assessment perspective, rates of screening in at-risk populations would not be a useful quality indicator since the data are not strongly supportive of its effectiveness.
Threshold for repair Optimal quality for patients with AAAs involves referral for operation at the appropriate size threshold. Since AAA repair is performed to prevent rupture, the time at which the risk of rupture is greater than the risk of death from operation is generally regarded as the appropriate time for repair. This threshold for repair of AAAs has traditionally been when the maximal aortic diameter reaches 5 cm. However, recent evidence has emerged providing further guidance in choosing the appropriate size
Matrix of quality assessment for surgical patients Structure
Process
Outcome
Preoperative
Volume-based referral
Intraoperative
Available technology Anesthesia specialists
Optimization Preparation Mortality Complications
Postoperative
ICU physician staffing Nurse-to-patient ratios
Pulmonary testing Cardiac evaluation Antibiotics Surgical technique Anesthesia skill Early extubation Resuscitation Monitoring Nutrition
332
Mortality Complications Quality of life Satisfaction
CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5
The quality of care for patients with abdominal aortic aneurysms: Justin B. Dimick and Gilbert R. Upchurch Jr.
threshold for repairing AAAs. The Aneurysm Detection and Management (ADAM) trial compared the outcomes associated with immediate surgical repair with those associated with long-term surveillance in patients with asymptomatic AAAs less than 5.5 cm in diameter [8]. The study found that there was no significant difference in overall survival between the two treatment groups after 5 years of follow-up. This study reinforces previous data from the United Kingdom Small Aneurysm Trial, which also demonstrated no survival advantage for early surgical repair compared to surveillance during a similar period of follow-up [9]. Wide regional variations in the rate of AAA repair exist and likely reflect, at least in part, differences in practice patterns regarding the threshold for operation. For example, data from the Dartmouth Atlas of Vascular Health Care demonstrate that rates of elective AAA repair vary four-fold across hospital referral regions in the United States: from 0.37 per 1000 Medicare enrollees in Grand Junction, CO to 1.54 per 1000 enrollees in Odessa, TX [3]. These regional differences are likely to be due to variation in the intensity of diagnostic testing, as well as differences in physician practice. Surgeons in some geographic regions with high rates may be operating on patients with small aneurysms (overuse or misuse) and some regions may not be offering operate even when aneurysms are above appropriate thresholds (underuse). The large randomized trials discussed above provide a strong evidence base for appropriateness criteria that can be used in future studies to investigate the contribution of overuse, underuse, and misuse to variation in rates of aneurysm surgery.
Choice of open vs. endovascular open repair The last decade has witnessed a paradigm shift in the treatment of AAAs in the United States. Each year, endovascular repair of AAA occupies an increasing share of the market. Diffusion of this new technology has penetrated most geographic areas and is generally available across the United States. Operative mortality rates are either equivalent or lower for endovascular repair, and the endovascular approach is associated with marked reductions in postoperative complications and length of stay [10]. It appears that this new technology may prove to be durable with long-term follow-up (4 years) showing a freedom from aneurysm-related death rate of 97% with a 14% persistent endoleak rate [11]. The tradeoff associated with the lower short-term morbidity rate of endovascular repair is the need for long-term surveillence and potential repeat intervention for endoleaks. These issues should be carefully discussed with each patient before the decision is made to pursue endovascular repair. Despite this caveat, current clinical practice is to offer endograft repair CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5
to patients who are anatomical candidates. Patients with pararenal and suprarenal aneurysms are presently not candidates for FDA-approved endovascular grafting and therefore should be referred for open repair. Since endovascular AAA repair has superior shortterm outcomes compared to open repair, the threshold for repair may be altered by the introduction of this new procedure. Using decision analysis techniques, Finlayson et al. investigated the impact of endovascular AAA repair on life expectancy to determine if the optimal threshold of repair given certain patient characteristics should be adjusted [12]. The authors found that for patients in good health (average operative risk) the threshold for repair was not changed significantly. However, for older patients in poor health (high operative risk) there was a significant difference in the threshold for repair in the conventional (8.1cm) vs. endovascular (5.7cm) patient groups [12]. These data indicate that for older patients with poor health, the endovascular approach should be favored. However, despite the superiority of endovascular repair in this group, the benefit of surgery is very small in this group of patients (0.2 QALYs) [12].
Provider characteristics and outcomes One current area of intense debate is the relationship between provider (surgeon or hospital) volume and quality of care. Skepticism about the relationship of volume to outcome in health care is based on the lack of adjustment for clinical differences between high and low volume centers. Population-based studies on the volume–outcome effect are largely derived from state and national administrative datasets, but there are a number of reports with rigorous clinical case-mix adjustment. The majority of reports, including those with robust risk adjustment, demonstrate a variable, but persistent relationship of higher procedural volume with improved outcomes [13]. Several surgical procedures have superior outcomes when performed at high volume centers, with more technically complex procedures showing a stronger relationship with volume [1–3]. One of the strongest and most persistent relationships has been noted for AAA repair which has lead to health policy suggesting selective referral to high volume centers [1–3, 5]. Population-based analyses conducted at the state and national level reveal a variable but persistent relationship between surgeon specialty, provider volumes, and outcomes for AAA repair. Using the Florida hospital discharge database, Pearce and colleagues showed a 24% lower risk of death or complications when AAA repairs were performed by surgeons with American Board of Surgery certification for added qualifications in vascular surgery 333
The quality of care for patients with abdominal aortic aneurysms: Justin B. Dimick and Gilbert R. Upchurch Jr.
[14]. In this study, a significant independent relationship was also found between increasing hospital and surgeon volume and lower mortality [14]. In another study from Ontario, CA, Tu and others used Canadian Institute for Health Information hospital discharge data linked to the Ontario Registered Patients Database to calculate risk-adjusted 30-day mortality rates for AAA repair [15]. They demonstrated a 62% increased risk of mortality when AAA repair was performed by general surgeons compared to vascular surgeons and no difference between cardiac and vascular surgeons was found. Furthermore, low surgeon volume [(five cases per year) was associated with an 83% increased risk of mortality in the risk-adjusted analysis [15]. One of the most comprehensive analyses of provider volume and surgeon specialty for AAA repair can be found in the Dartmouth Atlas of Vascular Health Care [3]. Using the national Medicare database, the effect of surgeon volume and surgeon specialty on 30-day mortality rates for AAA repair was determined. These authors found that low volume surgeons (⬍4 per year) had significantly higher mortality rate (7.9%) compared to high volume surgeons (⬎10 per year) with a mortality rate of 4.0%. Surgical specialty was also associated with mortality, with vascular surgeons (4.4%) and cardiac surgeons (5.4%) having lower mortality rates than general surgeons (7.3%). One of the most striking findings in the analysis provided by the Dartmouth Atlas is the variation in surgeon specialty type and surgeon volume among the 306 hospital referral regions performing AAA repair. For example, nine regions had 0% of AAA repairs performed by vascular surgeons compared to 92% in Greensboro, North Carolina. Further, seven regions saw 0% of AAA repairs performed by general surgeons compared to 85% in Green Bay, Wisconsin. Given the strong association of provider volume and surgeon specialty with outcomes and the dramatic variation in who performs AAA repairs, many deaths could be potentially avoided by increasing the proportion of this procedure performed by vascular surgeons or high volume providers. The studies discussed above are taken from limited geographic areas or only enrollees in Medicare and may not be representative of the entire United States population. In contrast, a recent study performed by our group studied the independent contribution of each provider level variable in determining outcomes after AAA repair in the United States [16]. Overall AAA repair mortality in this nationally representative sample was 4.2%, being lower at high volume hospitals (3.0%) vs. low volume hospitals (5.5%) (P ⬍ 0.001). In addition, vascular surgeons had the lowest mortality (2.2%) compared to cardiac (4.0%) and general surgeons (5.5%) (P ⬍ 0.001). Mortality rates were also lower for high volume sur334
geons (2.5%) compared to low volume surgeons (5.6%) (P⬍0.001). In the multivariate analysis, high volume hospitals, surgeon specialty, and high volume surgeons were all independently associated with a lower risk of in-hospital mortality. In this analysis, the risk reduction was 30% for high volume hospitals and 40% for surgery by a high volume surgeon. AAA repair by general surgeons compared to vascular surgeons was associated with a 76% greater risk of mortality. No significant difference in mortality existed between cardiac and vascular surgeons [16]. These three provider–level variables are closely related, yet each represents an independent predictor of mortality. These data have driven health policy suggesting referral of patients in need of AAA repair to high volume hospitals (e.g. the Leapfrog group). However, such policy does not take into account differences in outcomes attributable to individual surgeon volume or surgical specialty, which are at least as important as hospital volume in determining outcomes. Critics of volume-based referral methods remind us that volume is only a surrogate for the quality of health care. One alternative to relying on volumebased referral is to directly measure and compare risk-adjusted outcome between medical centers. Such quality improvement programs have achieved and sustained reductions in operative mortality for cardiac surgery in New York State and New England [17, 18]. The National Surgical Quality Improvement Project (NSQIP) has provided an example for non-cardiac surgery within the Veterans Affairs Hospital System [19]. Since the inception of the NSQIP, there has been a 27% decline in the risk-adjusted 30day mortality rate and at 45% decline in the 30-day morbidity rate in VA medical centers [11]. A system directly measuring risk-adjusted outcomes would seem ideal since it avoids the necessity of relying on a surrogate, such as hospital or surgeon volume, to determine the quality of care at a given hospital. In addition, it avoids relying on administrative data for information regarding outcomes. Currently, the NSQIP methodology is being further expanded into several private sector medical centers to further document the utility of such a quality improvement tool outside the VA system. While direct measurement of outcomes to determine quality is appealing, there are several limitations of such an approach. For instance, not all medical centers have the resources to make the changes necessary to improve their quality. For instance, if optimal outcomes are due, at least in part, to more highly specialized nurses, anesthesiologists, and physicians, small hospitals may not have sufficient volume to allow staff to specialize to the degree that would be necessary to attain procedurespecific skills. In addition, certain technologies may be related to superior outcomes and, given that they CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5
The quality of care for patients with abdominal aortic aneurysms: Justin B. Dimick and Gilbert R. Upchurch Jr.
represent large capital investments, many medical centers may not be able to obtain them. With these and other limitations, the quality improvement cycle is impeded in some institutions. Another limitation is relying on the use of a summary quality measure for all surgical procedures at a given hospital. Very few surgical procedures are performed frequently enough so that precise estimates of mortality rates can be generated for a single hospital. For example, if a hospital performs 30 AAA repairs in a year and three patients die, is the mortality rate 10%? From a statistical viewpoint, the precision of this estimate would be best represented with a 95% confidence interval. Using this method, the true value of the proportion (3/30) has a 95% chance of being between 2 and 27%. This example illustrates that single hospital mortality rates are certainly not precise enough to make conclusions about the quality of care for that hospital. For the NSQIP, this imprecision is dealt with by grouping procedures together and creating a summary quality measure for all surgical services. In contrast, with volume-based referral policies, aggregating hospitals into volume groups for each procedure eliminates the imprecision of hospital-specific event rates. A final limitation of using risk-adjusted outcomes to determine quality is the high cost. Prospective data collection is expensive and nurse-reviewers would need to be trained and employed to perform the data collection; also, data management and analysis would require computer programmers and statisticians. Given this overhead, the cost-effectiveness of quality improvement initiatives would need to be demonstrated before they are widely implemented.
Summary Abdominal aortic aneurysm (AAA) repair is a complex surgical procedure and is commonly performed in a variety of practice settings across the United States. The quality of surgical care is neither ideal nor uniform across medical centers with documented variation in both utilization and outcomes. Recent data document that screening, though effective in reducing AAA-related deaths, may have only small contributions to population mortality. Large randomized trials have provided evidence regarding the timing of AAA repair and provide strong evidence for the development of appropriateness criteria. In general, lower mortality rates have been consistently associated with higher provider volume (surgeon and hospital) and specialization in vascular surgery. Current health policy initiatives suggest referral of several complex procedures to high volume centers based on minimum volume standards. Given that provider volume is only a surrogate for the quality of care, the use of risk-adjusted outcomes CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5
as measures of quality should be explored for vascular surgery.
References 1. Birkmeyer, J. D., Siewers, A. E., Finlayson, E. V. et al. Hospital volume and surgical mortality in the United States. N Engl J Med, 2002, 346, 1128–1137. 2. Dimick, J. B., Stanley, J. C., Axelrod, D. A. et al. Variation in death rate after abdominal aortic aneurysmectomy in the United States: Impact of hospital volume, gender, and age. Ann Surg, 2002, 235, 579–585. 3. Cronenwett, J. L. and Birkmeyer, J. D. eds, The Dartmouth Atlas of Vascular Health Care AHA Press, Chicago 1999. 4. Institute of Medicine. Crossing the Quality Chasm: A New Health System for the Twenty-first Century. National Academy Press, Washington, 2001. 5. Birkmeyer, J. D., Finlayson, E. V. and Birkmeyer, C. M. Volume standards for high-risk surgical procedures: potential benefits of the Leapfrog initiative. Surgery, 2001, 130, 415–422. 6. The Multicentre Aneurysm Screening Study Group. The Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial. Lancet, 2002, 60, 1531–1539. 7. The Multicentre Aneurysm Screening Study Group. Multicentre aneurysm screening study (MASS): cost effectiveness analysis of screening for abdominal aortic aneurysms based on four year results from randomised controlled trial. BMJ, 2002, 325, 1135. 8. Lederle, F. A., Wilson, S. E., Johnson, G. R. et al. Immediate repair compared with surveillance of small abdominal aortic aneurysms. New England Journal of Medicine, 2002, 346, 1437– 1444May 9. 9. The United Kingdom Small Aneurysm Trial Participants. Longterm outcomes of immediate repair compared with surveillance of small abdominal aortic aneurysms. New England Journal of Medicine, 2002, 346, 1445–1452. 10. Zarins, C. K., White, R. A., Schwarten, D. et al. AneuRx stent graft versus open surgical repair of abdominal aortic aneurysms: multicenter prospective clinical trial. Journal of Vascular Surgery, 1999, 29, 292–305. 11. Zarins, C. K. The US AneuRx Clinical Trial: 6-year clinical update 2002. Journal of Vascular Surgery, 2003, 37, 904–908. 12. Finlayson, S. R., Birkmeyer, J. D., Fillinger, M. F. et al. Should endovascular surgery lower the threshold for repair of abdominal aortic aneurysms? Journal of Vascular Surgery, 1999, 29, 973– 985. 13. Halm, E. A., Lee, C. and Chassin, M. R. Is volume related to outcome in health care? A systematic review and methodologic critique of the literature. Annals of Internal Medicine, 2002, 137, 511–520. 14. Tu, J. V., Austin, P. C. and Johnston, K. W. The influence of surgical specialty training on the outcomes of elective abdominal aortic aneurysm surgery. Journal of Vascular Surgery, 2001, 33, 447–452. 15. Pearce, W. H., Parker, M. A., Feinglass, J. et al. The importance of surgeon volume and training in outcomes for vascular surgical procedures. Journal of Vascular Surgery, 1999, 29, 768–776. 16. Dimick J.B., Cowan J.A., Stanley J.C. et al. Surgeon specialty and provider volumes are related to outcomes of abdominal aortic aneurysm repair in the United States. Journal of Vascular Surgery 2003, 38 (in press). 17. Chassin, M. R. Achieving and sustaining improved quality: lessons from New York State and cardiac surgery. Health Aff (Millwood), 2002, 21, 40–51. 18. O’Connor, G. T., Plume, S. K., Olmstead, E. M. et al. A regional intervention to improve the hospital mortality associated with coronary artery bypass graft surgery. The Northern New England Cardiovascular Disease Study Group. JAMA, 1996, 275, 841–846. 19. Khuri, S. F., Daley, J., Henderson, W. et al. The Department of
335
The quality of care for patients with abdominal aortic aneurysms: Justin B. Dimick and Gilbert R. Upchurch Jr. Veterans Affairs’ NSQIP: The first national validated, outcomebased, risk-adjusted, and peer-controlled program for the measurement and enhancement of the quality of surgical care. National VA Surgical Quality Improvement Program. Annals of Surgery, 1998, 228, 491–507.
336
Paper accepted 20 May 2003
CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5
Cardiovascular Surgery, Vol. 11, No. 5, pp. 331–336, 2003 2003 The International Society for Cardiovascular Surgery Published by Elsevier Ltd. All rights reserved. 0967-2109/03 $30.00
www.elsevier.com/locate/cardiosur
The quality of care for patients with abdominal aortic aneurysms Justin B. Dimick and Gilbert R. Upchurch Jr. University of Michigan Medical Center, Section of Vascular Surgery, 2210 Taubman Health Care Center, 1500 E. Medical Center Drive, Ann Arbor, MI, 48109-0329, USA Abdominal aortic aneurysm (AAA) repair is a complex surgical procedure and is commonly performed in a variety of practice settings across the United States. The quality of surgical care is neither ideal nor uniform across medical centers with documented variation in both utilization and outcomes. Recent data document that screening, though effective in reducing AAA-related deaths, may have only small contributions to population mortality. Large randomized trials have provided evidence regarding the timing of AAA repair and provide strong evidence for the development of appropriateness criteria. In general, lower mortality rates have been consistently associated with higher provider volume (surgeon and hospital) and specialization in vascular surgery. Current health policy initiatives suggest referral of several complex procedures to high volume centers based on minimum volume standards. Processes of care of high-volume providers and vascular surgeons should be studied and used to guide quality improvement efforts for lower volume providers and surgeons of other specialties performing AAA repair. 2003 The International Society for Cardiovascular Surgery. Published by Elsevier Ltd. All rights reserved. Keywords: abdominal aortic aneurysms, quality of care, screening, detection
Introduction The quality of care for patients with vascular disease varies across medical centers [1–3]. Rates of postoperative complications and operative mortality, for instance, differ widely across hospitals for most highrisk surgical procedures, with some of the largest differences observed for abdominal aortic aneurysm (AAA) repair [1–3]. In the United States, a recent report from the Institute of Medicine (IOM) has highlighted these differences between medical centers [4]. As a result, many stakeholders (e.g. patients and payers) are interested in holding physicians and hospitals accountable for providing high quality health care. Abdominal aortic aneurysms are a common cliniCorrespondence to: G.R. Upchurch. Tel.: +1-734-936-5790; fax: +1734-647-8967; e-mail: [email protected]
CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5
cal problem encountered by a variety of healthcare professionals. The quality of care for patients with the AAAs is potentially related to screening and recognition in at-risk populations, and is certainly dependent upon the appropriate timing of repair and optimal outcomes of the surgical repair. The objective of the current review is to discuss emerging evidence in each of these areas in the context of the quality of care for patients with AAAs. The diffusion of endovascular technology has implications on changes in both utilization and outcomes of AAA repair and these are considered in the discussion. When assessing the quality of care, it is important to maintain a distinction between structure, process, and outcomes of a provider–patient encounter. Structure relates to the material resources, human resources, and organizational structure of a health care organization; process relates to what is done to and for the patient; and outcome is how the process and structure allow patients to achieve desired 331
The quality of care for patients with abdominal aortic aneurysms: Justin B. Dimick and Gilbert R. Upchurch Jr.
changes in health status. Structural attributes associated with improved outcomes after complex aortic surgery include provider experience (hospital or surgeon volume), anesthesia specialists, and intensive care unit physician and nurse staffing. At least in part, organizational structure leads to improved quality through promotion and practice of more effective processes of care. In considering the process of care it is important to recognize three distinct areas, which include the preoperative, intraoperative, and postoperative phases of care. For AAA repair, several health care processes can be linked to improved outcomes during each stage. Examples include the appropriate cardiac and pulmonary evaluation and optimization before the operation (preoperative phase), use of perioperative antibiotics, resuscitation, and surgical technique (intraoperative phase), and invasive monitoring, ongoing resuscitation, and the prompt diagnosis and management of complications (postoperative phase) (Table 1).
Detection and screening The natural history of AAAs is characterized by progressive expansion and eventual rupture. Rupture of an AAA is associated with an extremely high mortality rate. Even patients fortunate enough to make it to the operating room experience a 50% operative mortality rate [2]. Consequently, the objective of surgical replacement of the aorta is to prevent rupture. Screening for AAAs, in theory, should increase the proportion undergoing elective repair and reduce the population-based mortality rate of this disease process. Many AAAs are currently detected either on physical exam (pulsatile abdominal mass) or incidentally on abdominal imaging (e.g. ultrasounds, computed tomography) performed for another reason. Screening in at-risk groups, such as elderly men with hypertension, is recommended but very few largescale organized screening efforts currently exist. The recent publication of the Multicentre Aneurysm Screening Study (MASS) provides good evidence that screening efforts aimed at older men would reduce AAA-related rupture and death [6]. Table 1
This large trial randomized more than 60 000 elderly men (65 to 74 years old) to be invited or not invited to receive ultrasound screening. The majority of men (80%) who were invited volunteered to have screening performed. Those with AAAs were continually followed with ultrasound for a mean of 4.1 years and those with aneurysms greater than 5.5 cm were offered elective repair. As a result, there was a significant reduction in AAA-related deaths (42% relative reduction) in the group who received screening. In a related cost-effectiveness analysis, the authors concluded that the additional cost of the screening program was $98 per person [7]. Over 4 years, the overall cost-effectiveness was found to be $57 700 per quality adjusted life year (QALY). Importantly, after 10 years, the authors concluded that figure would drop to $12 800 per QALY, which is well below the threshold considered to be cost-effective. However, when examining the absolute risk difference between the two groups (0.19 vs. 0.33%) the actual benefits of universal screening appear small. For example, 712 patients (95% CI, 500 to 1000) would have to be screened to prevent one AAArelated death [6]. Thus, until specific groups of patients at higher risk of rupture can be identified, screening for AAA repair should be seen as an acceptable, but not mandatory measure. From a quality assessment perspective, rates of screening in at-risk populations would not be a useful quality indicator since the data are not strongly supportive of its effectiveness.
Threshold for repair Optimal quality for patients with AAAs involves referral for operation at the appropriate size threshold. Since AAA repair is performed to prevent rupture, the time at which the risk of rupture is greater than the risk of death from operation is generally regarded as the appropriate time for repair. This threshold for repair of AAAs has traditionally been when the maximal aortic diameter reaches 5 cm. However, recent evidence has emerged providing further guidance in choosing the appropriate size
Matrix of quality assessment for surgical patients Structure
Process
Outcome
Preoperative
Volume-based referral
Intraoperative
Available technology Anesthesia specialists
Optimization Preparation Mortality Complications
Postoperative
ICU physician staffing Nurse-to-patient ratios
Pulmonary testing Cardiac evaluation Antibiotics Surgical technique Anesthesia skill Early extubation Resuscitation Monitoring Nutrition
332
Mortality Complications Quality of life Satisfaction
CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5
The quality of care for patients with abdominal aortic aneurysms: Justin B. Dimick and Gilbert R. Upchurch Jr.
threshold for repairing AAAs. The Aneurysm Detection and Management (ADAM) trial compared the outcomes associated with immediate surgical repair with those associated with long-term surveillance in patients with asymptomatic AAAs less than 5.5 cm in diameter [8]. The study found that there was no significant difference in overall survival between the two treatment groups after 5 years of follow-up. This study reinforces previous data from the United Kingdom Small Aneurysm Trial, which also demonstrated no survival advantage for early surgical repair compared to surveillance during a similar period of follow-up [9]. Wide regional variations in the rate of AAA repair exist and likely reflect, at least in part, differences in practice patterns regarding the threshold for operation. For example, data from the Dartmouth Atlas of Vascular Health Care demonstrate that rates of elective AAA repair vary four-fold across hospital referral regions in the United States: from 0.37 per 1000 Medicare enrollees in Grand Junction, CO to 1.54 per 1000 enrollees in Odessa, TX [3]. These regional differences are likely to be due to variation in the intensity of diagnostic testing, as well as differences in physician practice. Surgeons in some geographic regions with high rates may be operating on patients with small aneurysms (overuse or misuse) and some regions may not be offering operate even when aneurysms are above appropriate thresholds (underuse). The large randomized trials discussed above provide a strong evidence base for appropriateness criteria that can be used in future studies to investigate the contribution of overuse, underuse, and misuse to variation in rates of aneurysm surgery.
Choice of open vs. endovascular open repair The last decade has witnessed a paradigm shift in the treatment of AAAs in the United States. Each year, endovascular repair of AAA occupies an increasing share of the market. Diffusion of this new technology has penetrated most geographic areas and is generally available across the United States. Operative mortality rates are either equivalent or lower for endovascular repair, and the endovascular approach is associated with marked reductions in postoperative complications and length of stay [10]. It appears that this new technology may prove to be durable with long-term follow-up (4 years) showing a freedom from aneurysm-related death rate of 97% with a 14% persistent endoleak rate [11]. The tradeoff associated with the lower short-term morbidity rate of endovascular repair is the need for long-term surveillence and potential repeat intervention for endoleaks. These issues should be carefully discussed with each patient before the decision is made to pursue endovascular repair. Despite this caveat, current clinical practice is to offer endograft repair CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5
to patients who are anatomical candidates. Patients with pararenal and suprarenal aneurysms are presently not candidates for FDA-approved endovascular grafting and therefore should be referred for open repair. Since endovascular AAA repair has superior shortterm outcomes compared to open repair, the threshold for repair may be altered by the introduction of this new procedure. Using decision analysis techniques, Finlayson et al. investigated the impact of endovascular AAA repair on life expectancy to determine if the optimal threshold of repair given certain patient characteristics should be adjusted [12]. The authors found that for patients in good health (average operative risk) the threshold for repair was not changed significantly. However, for older patients in poor health (high operative risk) there was a significant difference in the threshold for repair in the conventional (8.1cm) vs. endovascular (5.7cm) patient groups [12]. These data indicate that for older patients with poor health, the endovascular approach should be favored. However, despite the superiority of endovascular repair in this group, the benefit of surgery is very small in this group of patients (0.2 QALYs) [12].
Provider characteristics and outcomes One current area of intense debate is the relationship between provider (surgeon or hospital) volume and quality of care. Skepticism about the relationship of volume to outcome in health care is based on the lack of adjustment for clinical differences between high and low volume centers. Population-based studies on the volume–outcome effect are largely derived from state and national administrative datasets, but there are a number of reports with rigorous clinical case-mix adjustment. The majority of reports, including those with robust risk adjustment, demonstrate a variable, but persistent relationship of higher procedural volume with improved outcomes [13]. Several surgical procedures have superior outcomes when performed at high volume centers, with more technically complex procedures showing a stronger relationship with volume [1–3]. One of the strongest and most persistent relationships has been noted for AAA repair which has lead to health policy suggesting selective referral to high volume centers [1–3, 5]. Population-based analyses conducted at the state and national level reveal a variable but persistent relationship between surgeon specialty, provider volumes, and outcomes for AAA repair. Using the Florida hospital discharge database, Pearce and colleagues showed a 24% lower risk of death or complications when AAA repairs were performed by surgeons with American Board of Surgery certification for added qualifications in vascular surgery 333
The quality of care for patients with abdominal aortic aneurysms: Justin B. Dimick and Gilbert R. Upchurch Jr.
[14]. In this study, a significant independent relationship was also found between increasing hospital and surgeon volume and lower mortality [14]. In another study from Ontario, CA, Tu and others used Canadian Institute for Health Information hospital discharge data linked to the Ontario Registered Patients Database to calculate risk-adjusted 30-day mortality rates for AAA repair [15]. They demonstrated a 62% increased risk of mortality when AAA repair was performed by general surgeons compared to vascular surgeons and no difference between cardiac and vascular surgeons was found. Furthermore, low surgeon volume [(five cases per year) was associated with an 83% increased risk of mortality in the risk-adjusted analysis [15]. One of the most comprehensive analyses of provider volume and surgeon specialty for AAA repair can be found in the Dartmouth Atlas of Vascular Health Care [3]. Using the national Medicare database, the effect of surgeon volume and surgeon specialty on 30-day mortality rates for AAA repair was determined. These authors found that low volume surgeons (⬍4 per year) had significantly higher mortality rate (7.9%) compared to high volume surgeons (⬎10 per year) with a mortality rate of 4.0%. Surgical specialty was also associated with mortality, with vascular surgeons (4.4%) and cardiac surgeons (5.4%) having lower mortality rates than general surgeons (7.3%). One of the most striking findings in the analysis provided by the Dartmouth Atlas is the variation in surgeon specialty type and surgeon volume among the 306 hospital referral regions performing AAA repair. For example, nine regions had 0% of AAA repairs performed by vascular surgeons compared to 92% in Greensboro, North Carolina. Further, seven regions saw 0% of AAA repairs performed by general surgeons compared to 85% in Green Bay, Wisconsin. Given the strong association of provider volume and surgeon specialty with outcomes and the dramatic variation in who performs AAA repairs, many deaths could be potentially avoided by increasing the proportion of this procedure performed by vascular surgeons or high volume providers. The studies discussed above are taken from limited geographic areas or only enrollees in Medicare and may not be representative of the entire United States population. In contrast, a recent study performed by our group studied the independent contribution of each provider level variable in determining outcomes after AAA repair in the United States [16]. Overall AAA repair mortality in this nationally representative sample was 4.2%, being lower at high volume hospitals (3.0%) vs. low volume hospitals (5.5%) (P ⬍ 0.001). In addition, vascular surgeons had the lowest mortality (2.2%) compared to cardiac (4.0%) and general surgeons (5.5%) (P ⬍ 0.001). Mortality rates were also lower for high volume sur334
geons (2.5%) compared to low volume surgeons (5.6%) (P⬍0.001). In the multivariate analysis, high volume hospitals, surgeon specialty, and high volume surgeons were all independently associated with a lower risk of in-hospital mortality. In this analysis, the risk reduction was 30% for high volume hospitals and 40% for surgery by a high volume surgeon. AAA repair by general surgeons compared to vascular surgeons was associated with a 76% greater risk of mortality. No significant difference in mortality existed between cardiac and vascular surgeons [16]. These three provider–level variables are closely related, yet each represents an independent predictor of mortality. These data have driven health policy suggesting referral of patients in need of AAA repair to high volume hospitals (e.g. the Leapfrog group). However, such policy does not take into account differences in outcomes attributable to individual surgeon volume or surgical specialty, which are at least as important as hospital volume in determining outcomes. Critics of volume-based referral methods remind us that volume is only a surrogate for the quality of health care. One alternative to relying on volumebased referral is to directly measure and compare risk-adjusted outcome between medical centers. Such quality improvement programs have achieved and sustained reductions in operative mortality for cardiac surgery in New York State and New England [17, 18]. The National Surgical Quality Improvement Project (NSQIP) has provided an example for non-cardiac surgery within the Veterans Affairs Hospital System [19]. Since the inception of the NSQIP, there has been a 27% decline in the risk-adjusted 30day mortality rate and at 45% decline in the 30-day morbidity rate in VA medical centers [11]. A system directly measuring risk-adjusted outcomes would seem ideal since it avoids the necessity of relying on a surrogate, such as hospital or surgeon volume, to determine the quality of care at a given hospital. In addition, it avoids relying on administrative data for information regarding outcomes. Currently, the NSQIP methodology is being further expanded into several private sector medical centers to further document the utility of such a quality improvement tool outside the VA system. While direct measurement of outcomes to determine quality is appealing, there are several limitations of such an approach. For instance, not all medical centers have the resources to make the changes necessary to improve their quality. For instance, if optimal outcomes are due, at least in part, to more highly specialized nurses, anesthesiologists, and physicians, small hospitals may not have sufficient volume to allow staff to specialize to the degree that would be necessary to attain procedurespecific skills. In addition, certain technologies may be related to superior outcomes and, given that they CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5
The quality of care for patients with abdominal aortic aneurysms: Justin B. Dimick and Gilbert R. Upchurch Jr.
represent large capital investments, many medical centers may not be able to obtain them. With these and other limitations, the quality improvement cycle is impeded in some institutions. Another limitation is relying on the use of a summary quality measure for all surgical procedures at a given hospital. Very few surgical procedures are performed frequently enough so that precise estimates of mortality rates can be generated for a single hospital. For example, if a hospital performs 30 AAA repairs in a year and three patients die, is the mortality rate 10%? From a statistical viewpoint, the precision of this estimate would be best represented with a 95% confidence interval. Using this method, the true value of the proportion (3/30) has a 95% chance of being between 2 and 27%. This example illustrates that single hospital mortality rates are certainly not precise enough to make conclusions about the quality of care for that hospital. For the NSQIP, this imprecision is dealt with by grouping procedures together and creating a summary quality measure for all surgical services. In contrast, with volume-based referral policies, aggregating hospitals into volume groups for each procedure eliminates the imprecision of hospital-specific event rates. A final limitation of using risk-adjusted outcomes to determine quality is the high cost. Prospective data collection is expensive and nurse-reviewers would need to be trained and employed to perform the data collection; also, data management and analysis would require computer programmers and statisticians. Given this overhead, the cost-effectiveness of quality improvement initiatives would need to be demonstrated before they are widely implemented.
Summary Abdominal aortic aneurysm (AAA) repair is a complex surgical procedure and is commonly performed in a variety of practice settings across the United States. The quality of surgical care is neither ideal nor uniform across medical centers with documented variation in both utilization and outcomes. Recent data document that screening, though effective in reducing AAA-related deaths, may have only small contributions to population mortality. Large randomized trials have provided evidence regarding the timing of AAA repair and provide strong evidence for the development of appropriateness criteria. In general, lower mortality rates have been consistently associated with higher provider volume (surgeon and hospital) and specialization in vascular surgery. Current health policy initiatives suggest referral of several complex procedures to high volume centers based on minimum volume standards. Given that provider volume is only a surrogate for the quality of care, the use of risk-adjusted outcomes CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5
as measures of quality should be explored for vascular surgery.
References 1. Birkmeyer, J. D., Siewers, A. E., Finlayson, E. V. et al. Hospital volume and surgical mortality in the United States. N Engl J Med, 2002, 346, 1128–1137. 2. Dimick, J. B., Stanley, J. C., Axelrod, D. A. et al. Variation in death rate after abdominal aortic aneurysmectomy in the United States: Impact of hospital volume, gender, and age. Ann Surg, 2002, 235, 579–585. 3. Cronenwett, J. L. and Birkmeyer, J. D. eds, The Dartmouth Atlas of Vascular Health Care AHA Press, Chicago 1999. 4. Institute of Medicine. Crossing the Quality Chasm: A New Health System for the Twenty-first Century. National Academy Press, Washington, 2001. 5. Birkmeyer, J. D., Finlayson, E. V. and Birkmeyer, C. M. Volume standards for high-risk surgical procedures: potential benefits of the Leapfrog initiative. Surgery, 2001, 130, 415–422. 6. The Multicentre Aneurysm Screening Study Group. The Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial. Lancet, 2002, 60, 1531–1539. 7. The Multicentre Aneurysm Screening Study Group. Multicentre aneurysm screening study (MASS): cost effectiveness analysis of screening for abdominal aortic aneurysms based on four year results from randomised controlled trial. BMJ, 2002, 325, 1135. 8. Lederle, F. A., Wilson, S. E., Johnson, G. R. et al. Immediate repair compared with surveillance of small abdominal aortic aneurysms. New England Journal of Medicine, 2002, 346, 1437– 1444May 9. 9. The United Kingdom Small Aneurysm Trial Participants. Longterm outcomes of immediate repair compared with surveillance of small abdominal aortic aneurysms. New England Journal of Medicine, 2002, 346, 1445–1452. 10. Zarins, C. K., White, R. A., Schwarten, D. et al. AneuRx stent graft versus open surgical repair of abdominal aortic aneurysms: multicenter prospective clinical trial. Journal of Vascular Surgery, 1999, 29, 292–305. 11. Zarins, C. K. The US AneuRx Clinical Trial: 6-year clinical update 2002. Journal of Vascular Surgery, 2003, 37, 904–908. 12. Finlayson, S. R., Birkmeyer, J. D., Fillinger, M. F. et al. Should endovascular surgery lower the threshold for repair of abdominal aortic aneurysms? Journal of Vascular Surgery, 1999, 29, 973– 985. 13. Halm, E. A., Lee, C. and Chassin, M. R. Is volume related to outcome in health care? A systematic review and methodologic critique of the literature. Annals of Internal Medicine, 2002, 137, 511–520. 14. Tu, J. V., Austin, P. C. and Johnston, K. W. The influence of surgical specialty training on the outcomes of elective abdominal aortic aneurysm surgery. Journal of Vascular Surgery, 2001, 33, 447–452. 15. Pearce, W. H., Parker, M. A., Feinglass, J. et al. The importance of surgeon volume and training in outcomes for vascular surgical procedures. Journal of Vascular Surgery, 1999, 29, 768–776. 16. Dimick J.B., Cowan J.A., Stanley J.C. et al. Surgeon specialty and provider volumes are related to outcomes of abdominal aortic aneurysm repair in the United States. Journal of Vascular Surgery 2003, 38 (in press). 17. Chassin, M. R. Achieving and sustaining improved quality: lessons from New York State and cardiac surgery. Health Aff (Millwood), 2002, 21, 40–51. 18. O’Connor, G. T., Plume, S. K., Olmstead, E. M. et al. A regional intervention to improve the hospital mortality associated with coronary artery bypass graft surgery. The Northern New England Cardiovascular Disease Study Group. JAMA, 1996, 275, 841–846. 19. Khuri, S. F., Daley, J., Henderson, W. et al. The Department of
335
The quality of care for patients with abdominal aortic aneurysms: Justin B. Dimick and Gilbert R. Upchurch Jr. Veterans Affairs’ NSQIP: The first national validated, outcomebased, risk-adjusted, and peer-controlled program for the measurement and enhancement of the quality of surgical care. National VA Surgical Quality Improvement Program. Annals of Surgery, 1998, 228, 491–507.
336
Paper accepted 20 May 2003
CARDIOVASCULAR SURGERY
OCTOBER 2003 VOL 11 NO 5