The effect of hospital vascular operation capability on outcomes of lower extremity arterial bypass graft procedures

The effect of hospital vascular operation capability on outcomes of lower extremity arterial bypass graft procedures James L. Ebaugh, MD, Joe Feinglass, PhD, and William H. Pearce, MD, Chicago, Ill

Background. The purpose of this study was to determine whether hospitals with a high capability for vascular operations have lower rates of inpatient mortality, major complication, and major amputation with lower extremity arterial bypass (LEAB) procedures than do less well-equipped hospitals after controlling for hospital procedure volume and patient characteristics. Methods. Admissions of 16,422 northern Illinois residents to Illinois hospitals for aortoiliac (AI) or distal bypass operations during 1993 to 1999 were analyzed. Hospitals were considered to have a high capability for vascular operations if they had cardiac surgical facilities and either an accredited blood flow laboratory, general surgical residency, or fellowship training in vascular surgery. Logistic regression was used to model the effect of hospital capability on mortality after controlling for hospital LEAB procedure volume, operation level, severity of illness, age, sex, and emergent admission. Results. Sixteen of 98 Illinois hospitals with 34.4% of the sample patients, including 8 of 18 hospitals with more than 40 admissions for LEAB procedures annually, were classified as having high surgical capability. Hospitals classified as having high versus low capability had lower mortality (2.8% vs 3.7%; P = .003) and amputation rates (4.6% vs 4.9% [not significant]) but higher major complication rates (9.8% vs 8.5%; P = .006). Conclusions. Mortality outcomes for LEAB procedures were superior at high capability hospitals, even after controlling for patient characteristics, disease severity, and LEAB volume. Hospital complication rates were not correlated with mortality rates and may not be a meaningful measure of quality of care. (Surgery 2001;130:561-9.) From the Division of Vascular Surgery, Department of Surgery, Division of General Internal Medicine, and Institute for Health Services Research and Policy Studies, Northwestern University, Chicago, Ill

AS WITH MANY OTHER HIGH-RISK SURGICAL PROCEDURES, variation in mortality after a lower extremity arterial bypass (LEAB) graft has been linked to differences in surgeon and hospital procedure volume.1,2 Overall inpatient mortality rates for this procedure have been found to average about 3.6% in referral center studies3 and 3.3% in 2 large state claims data studies.1,2 Hospitals in which more than 40 LEAB operations are performed annually have been found to have better mortality outcomes, and mortality appears to decline further as volume increases.2 However, how hospital procedure volume directly affects quality of care remains speculative. Hospitals with higher volume may achieve better

Presented at the 58th Annual Meeting of the Central Surgical Association, Tucson, Ariz, March 7-10, 2001. Reprint requests: James L Ebaugh, MD, 1725 N Halsted St, Chicago, IL 60614. Copyright © 2001 by Mosby, Inc. 0039-6060/2001/$35.00 + 0 11/6/116907 doi:10.1067/msy.2001.116907

mortality rates because of their technological sophistication, the larger number of skilled health professionals they employ, and the range of facilities they provide to patients undergoing vascular operations. Conversely, hospitals with larger volumes may admit fewer severely ill patients and perform relatively more operations for disabling claudication as opposed to limb salvage. The purpose of this study was to determine whether LEAB procedure volume is the primary determinant of risk-adjusted mortality outcomes or whether more basic measures of hospital surgical capability better explain variation in death rates. Unlike previous population-based studies, this analysis of the LEAB procedure in northern Illinois hospitals was performed after controlling for potentially important differences in the severity of lower extremity disease and comorbid conditions. Although the focus is on mortality rates, data on major perioperative complication and amputation rates are also presented. Results provide evidence for the value of regulatory approaches to improve the outcomes of lower extremity bypass procedures.4-7 SURGERY 561

562 Ebaugh, Feinglass, and Pearce

METHODS Administrative data. Institutional Review Board approval for this study was obtained from Northwestern University. Administrative data on admissions of residents in the 9 Chicago, Ill, area counties of Cook, DuPage, Grundy, Kane, Kankakee, Kendall, Lake, McHenry, and Will to 98 Illinois hospitals between 1993 to 1999 were obtained from the Illinois Hospitals and Health Systems Association Compdata files. This database contains publicly mandated data for all Illinois residents discharged from Illinois hospitals. Data include patient demographics, admission source, discharge disposition, the principal and up to 8 secondary diagnoses, and up to 5 procedure codes for each admission based on the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM). Records were selected based on the presence of 1 of 2 procedure codes: (1) aorta-iliac-femoral bypass (code 39.25) (AI) or (2) other (peripheral) vascular shunt or bypass procedure (code 39.29, which is used for distal bypass procedures). In the analysis, records with both codes for the same admission were counted as aorta-iliac-femoral bypass. To ensure that the patient sample reflected operations and outcomes for lower extremity vascular disease, patients younger than 40 years were excluded from the analysis, as were patients with procedure codes for open heart procedures, trauma, neoplasms, and abdominal aortic aneurysms. Risk adjustment. There are no validated methods of assessing a patient’s severity of illness at admission for vascular procedures on the basis of administrative data. It is well known that chronic conditions may be undercoded for patients who die or have severe complications and that ICD-9 coding does not indicate whether a given condition was present at admission or the result of an inhospital complication.8,9 For a fair comparison of institutions, it is nevertheless critical to attempt to perform risk adjustment that takes into account surgical outcomes for the severity of both chronic comorbid illness and lower extremity vascular disease symptoms.10 To address this, we performed risk adjustment in this analysis empirically by stratifying mortality rates by the prevalence of conditions that were very likely (ie, 90% of the time) to have been present at admission for this patient population. Codes for selected chronic disease and lower extremity diagnoses that were deemed highly likely to have been present on admission are presented in Table I. These codes, through examination of their association with mortality rates, were used to empirically

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stratify inpatient mortality into 4 severity-of-illness risk groups. Patient age, sex, and admission status (emergent vs elective) were also included as dichotomous risk variables. Variables of hospital vascular operation capability. Hospital surgical capability, as reflected by the human and technical resources available to vascular surgeons, is often difficult to quantify and document directly. To assess this dimension, information on the surgical facilities and training characteristics of northern Illinois hospitals was derived from the American Hospital Association 1999 Annual Survey of Hospitals, the Graduate Medical Education Directory, and the Intersocietal Commission for the Accreditation of Vascular Laboratories (ICAVL). Hospitals were designated as having high capability for vascular operation if they had (1) cardiac surgical facilities (cardiac catheterization laboratory, facilities for an open heart operation, and cardiac intensive care unit) and (2) an ICAVL accredited blood flow laboratory, a general surgical residency training program, or a fellowship training program in vascular surgery. Hospitals were classified as having high procedure volume if they performed more than 280 LEAB procedures from 1993 to 1999 (an average of at least 40 procedures per year). It was expected that a large number of hospitals with high capability might not have high volume and vice versa. Outcomes. Three endpoints—inpatient mortality, inpatient complications, and major amputations (through foot, below and above knee) that occurred during the admission for bypass—were used as outcome measures after LEAB procedures. Major postoperative inpatient complications were defined as acute myocardial infarction, acute renal failure, stroke, or cardiac arrest that occurred during the same admission as for the bypass procedure. The codes for these complications are listed in Table II. The practice of using ICD-9 discharge abstract codes for determining in-hospital complications in surgical patients has recently been studied. Chart review studies corroborated 89% of ICD-9 codes for surgical complications, with only a very small proportion of codes found to be present on admission. Professional Review Organization physician reviewers found substandard (negligent) care in 29.5% of patients with complicated operations as opposed to identifying quality problems in only 2.1% of randomly selected surgical control patients.9 In addition to these major complication codes, we also included ICD-9 derived surgical quality indicator codes as publicly distributed by the US Agency for Healthcare Research and Quality (AHRQ).11

Ebaugh, Feinglass, and Pearce 563

Surgery Volume 130, Number 4 Table I. ICD-9 codes used to stratify 4 severity-of-illness risk levels Severity of illness level 1

2

3

4

Likely preoperative comorbidity

ICD-9-CM

Atherosclerosis with claudication, stricture of artery, hypertension, osteomyelitis, atherosclerosis with rest pain, old myocardial infarction, angina, or chronic ischemic heart disease Diabetes and diabetic complications; cellulitis of toe, leg, foot; atherosclerosis with ulceration; decubitus or lower extremity ulcer; atherosclerosis, other and unspecified; pulmonary heart diseases; chronic obstructive pulmonary disease; chronic airway obstruction; other aneurysm or arterial embolism; thrombosis Gangrene, atherosclerosis with gangrene, malignancy, existing cerebrovascular disease, aortic or other aneurysm Hypertensive heart, renal disease, congestive heart failure, chronic renal failure, hypertensive renal disease

Table II. Major complication codes Acute myocardial infarction Acute renal failure Stroke Cardiac arrest

410.0-410.91 584.0-584.9, 997.5 430-436, 997.02 427.5, 997.1

The incidence of AHRQ codes for complications, which include pneumonia, thromboembolism, gastrointestinal bleeding, pulmonary compromise, and acute myocardial infarction, was computed with a denominator of all surgical admissions and was presumed to be a screen for “avoidable adverse outcomes.” For this study, the overall AHRQ-indicator complication rate was computed after exclusion of urinary tract infection, because of potential coding bias, and graft failure, which could be a cause of admission. A more expansive definition of the probable “any” complication rate was then produced by combining the incidence of major complications with AHRQ-coded complications. The validity of complication coding was assessed by comparing mean length of stay (LOS) between patients with complicated and uncomplicated diagnoses. Finally, codes for above-knee amputations (84.17), belowknee amputations (84.15), and forefoot amputations (84.12) were counted. Statistical analysis. Chi-square tests were used to compare the associations between categorical variables and the incidence of mortality, major complications, and amputations. Multiple logistic regression analysis, including patient demographics, severity of illness, operation level, hospital procedure volume, and capability for a vascular operation, was performed to test the significance of

440.21, 447.1, 401.0-402.99, 405.0-405.99, 730.07, 730.16-730.17, 730.26-730.28, 440.22, 412.0, 413.0-414.9 250.0-250.9, 681.10-681.11, 682.60, 682.70, 440.23, 707.0, 707.1, 440.1, 440.20, 440.29, 440.33-440.49, 440.80, 440.90, 415.00, 416.80-416.90, 491.00-494.00, 496.00, 442.0-442.9, 444.0-444.99 785.40, 440.24, 140.00-171.99, 174.00-195.99, 200.00-208.99, 273.00, 273.30, 196.0-199.99, 433.0437.9, 441.0-442.98 404.0-404.99, 428.0-428.9, 585.0-586.0, 403.0-403.99

a hospital’s capability for vascular operations as a risk-adjusted predictor of mortality. Model discrimination was measured with the area under the receiver operating characteristic curve; 0.5 indicated no discrimination and 1, perfect discrimination. Model calibration was measured with the HosmerLemeshow goodness-of-fit test, which examines the association between deciles of regression-predicted (expected) versus observed outcomes. RESULTS Hospital characteristics. Table III categorizes the 98 Illinois hospitals according to the presence of variables for hospital vascular operations capability. High capability for vascular operation was defined as the presence of full cardiac surgical capability and the pressure of either surgical training programs or ICAVL accreditation. Although not shown in Table III, only 3 of the 16 hospitals with high capability and residency training programs did not have ICAVL accreditation; 4 of the hospitals with high capability had IACVL accreditation but did not have residency programs. The 3 hospitals with fellowship training in vascular surgery had the highest volume of bypass procedures and total surgical admissions. Total surgical volume decreased with the increasing prevalence of each capability variable. Only 8 of 18 (44%) hospitals with high volume (more than 40 annual admissions for bypass procedures) also had high capability for vascular operation, and only half (8/16) of the hospitals with high capability for vascular operation also had high LEAB volume (not shown in Table III).

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Table III. Hospital vascular operation capability: volume and outcomes at northern Illinois hospitals 1993-1999

Hospitals Total Fellowship in vascular surgery General surgical residency Accredited blood flow laboratory Open heart procedures Cardiac intensive care unit Cardiac catheterization laboratory High vascular operation capability*

98 3 (3%) 20 (20%) 21 (21%) 33 (34%) 34 (35%) 54 (55%) 16 (16%)

Mean (SD) total annual lower extremity bypass volume

Mean (SD) annual aorta-iliac-femoral bypass volume

Mean (SD) 1999 inpatient and outpatient surgical admissions

24 (23) 91 (20) 47 (28) 43 (29) 41 (24) 38 (21) 36 (22) 50 (28)

4 (4) 17 (6) 9 (7) 8 (7) 7 (5) 7 (5) 6 (5) 9 (7)

1108 (661) 2600 (602) 1713 (807) 1604 (726) 1481 (751) 1444 (622) 1296 (651) 1959 (692)

*Defined as presence of the following 3 variables—capability of open heart operation, cardiac catheterization laboratory, and cardiac intensive care unit—and at least one of the following 3—accredited blood flow laboratory, general surgical residents, or fellowship for vascular operations.

Table IV. Proportions of severity-of-illness levels and claudication codes according to hospital capability for vascular operation Low capability for vascular operations High capability for vascular operations

SOI 1

SOI 2

SOI 3

SOI 4*

1255 (11.6%) 615 (10.9%)

4449 (41.3%) 2287 (40.5%)

2911 (27%) 1668 (29.5%)

2158 (20%) 1079 (19.1%)

Claudication†

Total

1693 (15.7%) 640 (11.3%)

10773 5649

SOI, Severity of illness. *P = .006. †P < .001.

Patient characteristics and outcomes by hospital type. Table IV compares patients’ severity of illness in hospitals with high capability for vascular operation versus those with low capability. Hospitals with high capability had approximately the same distribution levels of severity of illness as the lowcapability hospitals, but fewer patients at the high-capacity hospitals had codes for claudication. A higher percentage (18.7%) of the LEAB procedures performed at hospitals with high capability were aortoiliac reconstructions compared with only 14.9% at the hospitals with low capability (P < .001). Table V stratifies patients according to severity of illness and claudication and indicates a steadily increasing mortality and complication rate, as would be expected. Patients assigned codes for distal bypass procedures had higher amputation rates than those assigned codes for aorta-iliac-femoral bypass procedures (5.4% vs 1.7%; P < .001). This is because codes for gangrene were much more common in patients with distal bypass procedures than in those with aorta-iliac-femoral bypass procedures (28.4% vs 10.8%; P < .001) (not shown in Table V). On the other hand, patients assigned codes for more proximal bypass procedures experienced higher mortality and complication rates. Patients who underwent distal bypass procedures and were assigned codes for claudication had only a 3.4%

major complication rate, whereas those who were not assigned codes for claudication had a 9.4% major complication rate (P < .001). Advanced age (older than 74 years) was predictive of higher mortality and complications. Mortality and complications were not affected by patient sex. Emergency admission nearly doubled mortality and amputation rates, and the major complication rate rose from 9.6% to 11.8% (P < .001). Differences in mortality and complication rates between hospitals with high versus low procedure volume did not reach statistical significance, and although there was a statistically significant drop in amputation rates at hospitals with high volume, the effect was small (5.2% vs 4.5%; P = .04). However, high capability for vascular operations was predictive of a 24% lower inpatient mortality rate (2.8% vs 3.7%; P = .003) but not amputation rates (4.6% vs 4.9%; P = .38). In contrast, major complication rates were significantly higher at hospitals with high capability (9.8% vs 8.5%; P = .006). Adding AHRQ-coded complications to the 4 major complication codes (see Table II) resulted in a modest difference in magnitude of complications but little difference in the trend of complications for any patient-level risk factor (see Table V). This suggests that a more expansive definition of complication incidence will roughly double the compli-

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Surgery Volume 130, Number 4

Table V. Rates of inpatient mortality, major complications, and major amputations by patient risk factors Bypass admissions Severity of comorbid conditions

Aorta-iliac-femoral bypass Age > 74 Male Emergent admission Hospital LE bypass volume > 40/y High hospital vascular surgical capability‡ Low hospital vascular surgical capability§ Total admissions

Mortality rate

Major complications

AHRQ-coded complications plus major complications

Amputations 

1

1870(11%)

1.0%*

4.1%*

10.0%*

0.2%*

2 3 4

6736(41%) 4579(28%) 3237(20%) 2657(16%)

1.8%* 3.8%* 7.5%* 4.6%*

4.5%* 6.8%* 23.9%* 10.8%*

12.0%* 15.0%* 34.7%* 22.8%*

0.9%* 10.1%* 8.3%* 1.7%*

4882(30%) 9402(57%) 3355(20%) 7460(45%)

5.4%* 3.3% 6.4%* 3.1%

10.9%* 8.9% 11.8%* 9.2%

19.8%* 16.9% 23.9%* 17

5.0% 4.5%† 8.6%* 4.5%†

5649(34%)

2.8%†

9.8%†

18.0%†

4.6%

10773(66%)

3.7%

8.5%

16.5%

4.9%

16422

3.4%

8.9%

17.0%

4.8%

*P < .001. †P < .05. ‡Admissions to hospitals (16/98) with the following three variables—open heart procedure capability, cardiac catheterization laboratory, and cardiac intensive care unit—and at least 1 of the following 3—accredited blood flow laboratory, general surgical residents, or vascular surgery fellows. §Admissions to hospitals (82/98) that do not meet the aforementioned criteria. ||Percentages of above-knee (1.2%), below-knee (1.8%), and through foot (2.1%) amputations did not significantly differ between hospitals with high capability versus those with low capability.

Table VI. Logistic regression results for mortality Patients SOI 1 SOI 2 SOI 3 SOI 4 Claudication Age > 74 y High-capability hospital Male Emergency admission Bypass volume > 40/y Aortoiliac bypass

11% 41% 28% 20% 14% 30% 34% 57% 20% 45% 16%

Death rate 1.0% 1.8% 3.8% 7.5% 0.9% 5.4% 2.8% 3.3% 6.4% 3.1% 4.6%

Odds ratio 1 1.3 2.5 5 0.3 1.9 0.73 1 2.1 1 2.1

95% Confidence intervals Ref category 0.8-2.2 1.5-4.1 3.1-8.2 0.2-0.5 1.6-2.3 0.60-0.90 0.8-1.2 1.7-2.5 0.8-1.2 1.7-2.6

SOI, Severity of illness.

cation rate without altering the effect of risk factors. Patients admitted with any complication code were compared with those without such a code. Mean LOS differed widely (10.6 to 16.6 days for patients with complicated cases, P < .001). Logistic regression results. Table VI presents results of the mortality model. Although high hospital LEAB procedure volume was not predictive of lower mortality in multiple logistic regression, high capability for vascular operation showed a statistically significant protective effect (odds ratio = .73; P = .001). The other variables had predictable

effects. Increasing severity of illness, increasing age, emergent admission, and aorta-iliac-femoral bypass procedures all showed significantly increased risk of death, and patients assigned claudication codes had approximately one third the likelihood of inpatient death. The overall model area under the receiver operating characteristic curve was 0.75, which is equivalent to or better than most validated coronary bypass procedure mortality models based on detailed clinical data.12 The Hosmer-Lemeshow was Χ2 = 13.3 (df = 8, P = .1), indicating moderate model calibration. Table VII

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Table VII. Deciles of mean regression-predicted versus mean observed mortality 1 2 3 4 5 6 7 8 9 10 Total

Admissions

Predicted

Observed

1642 1632 1840 1636 1509 1701 1638 1728 1692 1404 16422

0.5% 0.9% 1.3% 1.7% 2.2% 2.5% 3.4% 4.6% 6.5% 11.5% 3.4%

0.4% 0.8% 0.5% 1.8% 2.3% 2.9% 4.0% 5.0% 6.1% 11.3% 3.4%

presents deciles of regression-predicted versus observed mortality. Expected mortality rates were all within 0.8% of observed rates. CONCLUSIONS Higher hospital procedure volume and higher volume of operations per surgeon have been associated with lower mortality rates in many studies.1,2,6,13-15 However, the exclusive use of volume statistics as a proxy for quality may obscure the complexity of what produces superior patient outcomes.16 In this study, institutions with higher procedure volumes were about equally divided between hospitals identified as having high capability for vascular operations and those without equivalent cardiovascular operation, blood flow laboratory, and surgical training characteristics. In reviewing this distinction, it was apparent that some (10/18) highly respected suburban community hospitals with high procedure volume were not among the hospitals with high capability and that half (8/16) of the largely urban hospitals with high capability did not have high (more than 40 annual) LEAB procedure volume. Yet when controlling for both high volume and high capability simultaneously in the mortality model, high capability rather than high volume predicted superior mortality experience. Another counterintuitive finding was the discrepancy between complication and mortality rates. Despite recent attempts to standardize complications reporting at an institutional level,17 no consensus exists about which complications to include when assessing clinical outcomes after a vascular operation. Higher mortality rates did not predict higher complication rates in this study. This discrepancy is consistent with findings in patients who have undergone coronary artery bypass graft18 and mirrors findings of higher complication rates in large, teaching hospitals in California that are

equipped for open heart operations.19 This difference in complication and mortality outcomes could be a result of more extensive ICD-9 coding rates at teaching institutions, where multiple physicians see patients and document findings, or because hospitals with lower mortality keep alive patients with complicated cases who might die elsewhere. This is supported by the higher percentage of aortoiliac bypass procedures performed at the hospitals with high capability (lower mortality). Another factor may be that hospitals with higher capability perform a greater number of more distal anastomoses, which have been associated with higher complication (and amputation) rates.20 In any case, there is evidence from hospital structural quality measures that the mortality rate, rather than often ambiguously defined complication rates, is a better indicator for hospital surgical quality of care.9,21 The use of administrative data in predicting the quality of care at various hospitals has major limitations. First, inpatient mortality may not fully reflect mortality as measured from a fixed interval from operation (eg, 30 days), although this is unlikely to have introduced major bias for the patients studied. Secondly, ICD-9 coding is known to imperfectly reflect chart documentation, which varies among institutions, and different risk adjustment approaches yield differing predicted probabilities of death for the same patients.22 Because of this, the approach to risk adjustment used in this study relies on empirical evidence specific to patients who underwent lower extremity bypass procedures rather than existing, but not validated, generic computer software products. Finally, this study could not assess surgeon age, volume, or board certification. These surgeon factors have been found to influence outcomes for aortic aneurysm and carotid endarterectomy procedures;1 however, there is no evidence for their influence on LEAB outcomes. Hospital procedure volume has long been associated with lower mortality rates for vascular operation.5 However, procedure volume only partially explains regional and hospital variation in outcomes.10 Differences in the patients, physicians, and the structural quality of the hospitals must all be considered simultaneously when health care delivery is evaluated. Variation in comorbid conditions and the severity of limb ischemia are key factors in outcomes for patients who undergo lower extremity vascular procedures. Thus, volume may not be a primary predictor of outcome when it is not adjusted for risk. Regionalized care from hospitals approved to perform certain procedures has been advocated

Surgery Volume 130, Number 4 for selected complex surgical procedures.4,5 Whether this concept would benefit the outcomes of a vascular operation depends on further investigation into the complex factors involved in determining not only the endpoints studied here but also functional and long-term outcomes. Functional endpoints, such as quality of life, exercise capacity, and walking ability, would be considered more accurate measures of success after these operations but are best measured prospectively.23 However, mortality and complication rates are more readily and inexpensively available at the regional level. In any case, regulatory measures may be best tailored to hospital surgical capability rather than volume, per se. In summary, hospital characteristics play an important role in determining outcome for lower extremity bypass procedures. Hospitals with high procedure volume tend to have better outcomes than those with lower volume. However, in this study we found that hospitals with high capability but low procedure volumes had better outcomes than those with high volumes alone. This finding implies that factors other than volume are important determinants of quality of care. It is possible that in hospitals with high capability there exists a structured environment for patients with vascular disease. This structured environment would include dedicated nursing units, vascular nurse specialists, and perhaps vascular medicine specialists. Further study is needed to define the role of these individuals in determining clinical outcomes. As the vascular surgery community strives to improve patient care, careful attention should be given to each step of a patient’s treatment, ranging from the blood flow laboratory, angiography, the nursing units, and surgical intensive care units to postoperative management. Special thanks to Molly Campbell from the Northwestern Memorial Hospital Financial Planning Office for assistance in obtaining the Compdata files. REFERENCES 1. Pearce WH, Parker MA, Feinglass J, Ujiki M, Manheim LM. The importance of surgeon volume and training in outcomes for vascular surgical procedures. J Vasc Surg 1999;29:768-78. 2. Manheim LM, Sohn MW, Feinglass J, Ujiki M, Parker MA, Pearce WH. Hospital vascular surgery volume and procedure mortality rates in California, 1982-1994. J Vasc Surg 1998;28:45-58. 3. Hunink MGM, Wong JB, Donaldson MC, Meyerovitz MF, de Vries Jelle, Harrington DP. Revascularization for femoropopliteal disease: a decision and cost-effectiveness analysis. JAMA 1995;274:165-71. 4. Gordon TA, Burleyson GP, Tielsch JM, Cameron JL. The effects of regionalization on cost and outcome for one general high-risk surgical procedure. Ann Surg 1995;221:43-9.

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5. Luft HS, Bunker JP, Enthoven AC. Should operations be regionalized? The empirical relation between surgical volume and mortality. N Engl J Med 1979;301:1364-9. 6. Harmon JW, Tang DG, Gordon TA, Bowman HM, Choti MA, Kaufman HS, et al. Hospital volume can serve as a surrogate for surgeon volume for achieving excellent outcomes in colorectal resection. Ann Surg 1999;230:404-11. 7. O’Connor GT, Plume SK, Olmstead EM, Coffin LH, Morton JR, Maloney CT, et al. A regional prospective study of in-hospital mortality associated with coronary artery bypass grafting. JAMA 1991;266:803-9. 8. Iezzoni LI, Foley SM, Daley J, Hughes J, Fisher ES, Heeren T. Comorbidities, complications, and coding bias: does the number of diagnosis codes matter in predicting in-hospital mortality? JAMA 1992;267:2197-203. 9. Lawthers AG, McCarthy EP, Davis RB, Peterson LE, Palmer H, Iezzoni LI. Identification of in-hospital complications from claims data: is it valid? Med Care 2000;38:785-79. 10. Kazmers A, Jacobs L, Perkins A, Lindenauer SM, Bates E. Abdominal aortic aneurysm repair in Veterans Affairs medical centers. J Vasc Surg 1996;23:191-200. 11. Ball JK, Elixhauser A, Johantgen M, et al. HCUP quality indicators, methods, version 1.1: outcome, utilization, and access measures for quality improvement. Healthcare cost and utilization project (HCUP-3) research note. Rockville, MD: Agency for Health Care Policy and Research; 1998. AHCPR Publication No. 98-0035. 12. Fortescue EB, Kahn K, Bates DW. Prediction rules for complications in coronary bypass surgery: a comparison and methodological critique. Med Care 2000;38:820-35. 13. O’Neill L, Lanska DJ, Hartz A. Surgeon characteristics associated with mortality and morbidity following carotid endarterectomy. Neurology 2000;55:773-81. 14. Cebul RD, Snow RJ, Pine R, Hertzer NR, Norris D. Indications, outcomes, and provider volumes for carotid endarterectomy. JAMA 1998;279:1282-7. 15. Hughes RG, Hunt SS, Luft HS. Effects of surgeon volume and hospital volume on quality of care in hospitals. Med Care 1987;25:489-503. 16. Hannan EL. The relation between volume and outcome in health care. N Engl J Med 1999;340:1677-9. 17. Pomposelli JJ, Gupta SK, Zacharoulis DC, Landa R, Miller A, Nanda R. Surgical complication outcome (SCOUT) score: a new method to evaluate quality of care in vascular surgery. J Vasc Surg 1997;25:1007-15. 18. Silber JH, Rosenbaum PR, Schwartz S, Ross RN, Williams SV. Evaluation of the complication rate as a measure of quality of care in coronary artery bypass graft surgery. JAMA 1995;274: 317-23. 19. Iezzoni LI, Daley J, Heeren T, Foley SM, Hughes JS, Fisher ES, et al. Using administrative data to screen hospitals for high complication rates. Inquiry 1994;31:40-55. 20. Rhodes RS, Krasniak CL, Jones PK. Factors affecting length of hospital stay for femoropopliteal bypass: implications of the DRGs. N Engl J Med 1986;314:153-7. 21. Hartz AJ, Krakauer H, Kuhn AM, Young M, Jacobsen SJ, Gay G, et al. Hospital characteristics and mortality rates. N Engl J Med 1989;321:1720-5. 22. Iezzoni LI. The risks of risk adjustment. JAMA 1997; 278:1600-7. 23. Mann NC, Mullins RJ, MacKenzie EJ, Jurkovich GJ, Mock CN. Systematic review of published evidence regarding trauma system effectiveness. J Trauma Inj Inf Crit Care 1999;47:S25-33.

DISCUSSION Dr Lazar J. Greenfield (as read by Dr Darrell A. Campbell Jr of Ann Arbor, Mich) (Ann Arbor, Mich). I

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would like to congratulate Dr Ebaugh on his presentation and express my gratitude to the authors for a copy of the manuscript well in advance of the meeting. In this retrospective analysis, the authors have reviewed more than 16,000 admissions to Illinois hospitals for the outcome of bypass procedures for peripheral vascular disease. There is good evidence of a relationship between better clinical outcomes and high volume institutions in other surgical procedures, and it is logical to raise this issue for patients with vascular disease. The refinement they have added is to look beyond volumes alone to what they term high-surgical capability institutions. This was defined by the accommodation of cardiac surgery facilities and either an accredited vascular laboratory or a training program in general or vascular surgery. This selectivity raises the question as to whether there is any basis for the assumption that teaching institutions have higher quality outcomes for surgical patients than nonteaching facilities. The key to any valid assessment of outcomes is appropriate stratification of illness, which is problematic when ICD-9 coding is utilized. To address this, the authors have used 4 categories of illness, including atherosclerotic, diabetic, gangrene, and hypertensive cardiac or renal disease. However, there are also large ranges of severity within these disorders that make the labeling incomplete. Therefore, was any effort made to determine whether there were comparable severities of these disorders between the types of hospital systems analyzed? The outcomes of major complications or amputations were recorded only for the operative hospitalization, which would exclude any delayed poor outcomes. How comfortable are the authors with the assumption that all patients who survived the procedure to leave the hospital should be considered as having had a high quality outcome? Since only 44% of the high-volume hospitals were categorized as high capability, and only half of the highcapability hospitals had high volumes, what have the authors concluded about referral practices? There was a slightly higher severity of illness found in high-capability hospitals, which also had higher major complication rates, thought to reflect better documentation. In view of this, how do you explain the 24% lower mortality rate? Does this reflect better surgical and anesthetic technique, better postoperative physician care, or should nursing and better technology get the credit? Other studies have suggested that vascular board certification makes a difference in limb and patient survival in these patients, and the obvious question is whether there is any evidence that a higher proportion of vascular boarded surgeons are to be found in the highcapability versus the high-volume institutions. Finally, if the latter assumption is correct, can we expect outcomes to improve as the number of vascular certified surgeons increases in nonteaching hospitals? Dr Josef E. Fischer (Cincinnati, Ohio). This is a very interesting paper because it adds one particular dimension to what has become a cottage industry and the relationship between hospital volume and surgeon volumes to outcomes.

Surgery October 2001 We have to be very careful about this bandwagon because if you really read the papers of, for example, statewide analysis of data, there seem to be some elements of outcomes that I don’t think anyone understands. In some of the papers that I have reviewed recently and which have not been published because of author bias, there do seem to be some aspects that we don’t understand. Perhaps the surgeon’s capability may explain the data. I have several questions for the authors. One of the things that struck me about your stratification of risk was there was one element which, at least as far as vascular patients are concerned, I associate with increased mortality, and that is a cardiac event. Perhaps that is hidden in some of the stratifications, but I did not see in either SOI 1 to 4 a prior myocardial infarction, which probably is significant, at least in most series. Secondly, I wonder whether you analyzed your data on the basis of quartiles, because one of the things that you see when you look at data from analysis of other surgical procedures—including some very ordinary surgical procedures like breast surgery or colectomy and even in the very complex procedures like pancreatic duodenectomy—is that in the second quartile there are always surgeons and hospitals that have moderate volumes whose outcomes are just as good as those who have high volumes at high-volume hospitals, which suggests that there is an element of surgical skill. I wonder whether you analyzed your data on the basis of not high versus low but rather first, second, third, and fourth quartiles, which might actually be more instructive to try and analyze some of these different components. My last comment is a caution. Patients really don’t want to leave home for regionalization. And there is a long-term problem. If you go 400 miles away for your surgery and you have a late complication, nobody in the community is likely to take care of you. So I think we have got to be very careful before we advocate wholesale regionalization of even moderately complex procedures, which, seems to be advocated by the same people who brought us managed care. Dr William H. Baker (Maywood, Ill). I have 3 questions for you. Why did you include transmetatarsal amputations as a bad result? We have some bypass graft patients who come in with rather poor-looking feet, and I consider some of those patients who subsequently have a transmetatarsal amputation a success. Secondly, how far out did you follow the patients for an amputation? Does your data reflect only the same hospitalization? Some of our patients with failed grafts go home and come back later to have an amputation, sometimes within a month, sometimes within 2 months. I wonder if these latter patients were included in your failures. And thirdly—you can’t answer this question, but I am going to ask it anyhow. If I have a patient with intermittent claudication, I perform a grafting procedure and the graft occludes, the patient may not complain of claudication on the way out of the hospital and will have not

Surgery Volume 130, Number 4 had an amputation. The patient would be classified as a success even though I didn’t accomplish anything. Did you try to factor this scenario into your paper at all? Dr J. Jeffrey Alexander (Cleveland, Ohio). I think an important part of this discussion is an attempt to separate surgical skill from ancillary care and perioperative management. In discussing the higher-capability hospitals, meaning those hospitals that have more extensive cardiovascular programs, are we really talking about institutions promoting greater utilization of preoperative evaluation such as noninvasive stress testing, cardiology evaluation, and catheterization, which is not related to surgical skill? Is this reflected in the overall cost of managing these patients in the higher-capability hospitals? Dr Ebaugh. In reponse to Dr Greenfield’s first question, yes, we attempted to determine whether there were comparable rates of illness severity between the types of hospital systems analyzed and found that the distribution was approximately equal. As for using mortality as a marker for quality of care, it definitely has its limitations, but we believe it is more informative than using only complications, which can be unreliably coded depending on the institution. Because half of the high-volume hospitals were not high capability and vice versa, one can conclude that referral patterns do not follow along the assumption that more patients are referred to institutions with more resources. As for our conclusions regarding the referral practices having any effect on the referral of patients who had more claudication codes to the lower-capability hospitals, I think any comment we would make would be purely speculation. Possibly, the centers noted for their expertise in vascular surgery receive the patients with more critical ischemia indications and conservatively managed the claudication patients. There is no way to pinpoint who or what is responsible for the lower mortality rates at the high-capability hospitals, but we postulate that it is due to the combination of factors categorizing the hospitals as high capability. Further study is needed to address the other specific factors that you mention. Also, as for the comment about the higher rate of documentation at teaching or high-capability hospitals, this is thought to be partially due to the fact that there are more physicians making observations on each patient at these hospitals as opposed to the private hospitals, where it is usually just 1 or 2 physicians, and therefore more complications would be noted in teaching hospitals by ICD-9 coders. With regard to board certification between the highand low-capacity hospitals, this data set, unlike other data sets from other states such as Florida, we did not have valid information regarding board certification for the surgeons performing these operations. Analysis of

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the Florida data by Pearce et al, which was not risk adjusted, did not find a statistically significant lower mortality rate for this operation when performed by certified vascular surgeons, but looking at the combination of high capability and vascular board certification may show a difference. Dr Fischer, thank you for your comments. With regard to our stratification scheme and what was included in the severity of illness levels: in the severity of illness level 1, 6 different codes were included; in severity level 2, 11; and in SOI level 3, 5 different codes were included; and in the fourth level both congestive heart failure and chronic renal insufficiency were included. The SOI level 1 included codes for angina and chronic ischemic heart disease and the code for old MI. We did not stratify the 98 hospitals into quartiles of volume or capability. Although we observed lower mortality when hospitals had a high number of the capability variables, there was relatively equal mortality in those hospitals with 1, 2 or 3 of these, but in hospitals with 4 or more, there was an abrupt drop of about 1 percentage point, which formed the basis of our 2 groups of high and low capability. As for regionalization, all of our 98 northern Illinois hospitals were within less than 100 miles of each other. Many patients, including many of us here, would indeed be willing to travel to a referral center institution for a life-threatening operation if they knew quality was superior. the SOI level 1 included codes for angina and chronic ischemic heart disease and the code for old MI. As for Dr Baker’s question, we analyzed the data without transmetatarsal amputation included in the analysis, and there was no difference in terms of the pattern seen. So I think that transmetatarsal amputation could be left out and we would still arrive at the same conclusions. With regard to how far out the patients were followed, our data had information for one single admission, and we did not have any follow-up on these patients after their discharge. Codes for graft failure were not included in the analysis because they could have been either the cause of admission or a complication. The subsequent measures of success or failure to which you are referring were not detected by our study, which only counted failures as those patients who died, had a major amputation, or had one of the 4 specified complication codes during the index admission. Dr Alexander, you have touched on an important area for future study. Specialized nurses, cardiologists, and extensive ancillary resources could be responsible for the improved outcomes seen at these high-capability hospitals. The mean total charges for admissions to highcapability hospitals were 12% higher than to low-capability hospitals, while the length of stay was only 7% higher at the high-capability hospitals. This could be due to the higher resource utilization you are referring to.