Does it matter what a hospital is "high volume" for? Specificity of hospital volume-outcome associations for surgical procedures: analysis o
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《英国医生杂志》
1 Department of Surgery, University of Toronto, 200 Elizabeth Street, 9EN-236A, Toronto, ON M5G 2C4, Canada, 2 Department of Surgery, University of Minnesota Cancer Center, MMC 806, 420 Delaware Street SE, Minneapolis, MN 55455, USA
Correspondence to: D R Urbach david.urbach@uhn.on.ca
Abstract
Evidence that the short term outcomes of complex surgical procedures are better in hospitals that do high volumes of such procedures has prompted some authors to suggest that high risk surgery should be regionalised at high volume hospitals.1-5 Relatively little research has been done into the underlying mechanisms and the potential role of selection bias in surgical volume-outcome associations.6-10 Health policy measures advocating volume based regionalisation are, for the most part, predicated on the overwhelming empirical evidence of hospital volume-outcome associations.11 In general, policy initiatives have proposed that patients needing certain high risk surgical procedures should have them done in a hospital that performs a large volume of similar procedures.
The findings of volume-outcome studies are usually interpreted in the light of the conceptual framework of quality in health care proposed by Donabedian: structures, processes, and outcomes.12 High volume hospitals are assumed to have structural characteristics associated with better quality of care, and providers in these hospitals are thought to improve their processes of care through experience in providing complex care. Central to this framework is an implied linkage between the volume of a specific surgical procedure done in a hospital and the outcome of the same surgical procedure. The finding of improved outcome after pancreaticoduodenectomy in high volume hospitals has been uniformly attributed to the high volume of pancreaticoduodenectomy,3 13-15 not the volume of a different complex procedure, the volume of all complex procedures, or other hospital characteristics. Whether the volume-outcome association is unique to the combination of the volume and the outcome of the same procedure has never been tested. We sought to answer the question of whether the improved outcome observed in high volume hospitals was unique to the volume of the procedure of which the outcome is being assessed.
Methods
Patients and hospitals
During the five year study period, 31 632 patients had one of the five surgical procedures of interest (table 1). Patients undergoing oesophagectomy seemed to have the highest burden of comorbid illness (median Charlson score 4), whereas those having colorectal cancer resection or repair of an unruptured AAA had fewer comorbid conditions (median Charlson score 0). The largest preponderance of male patients was among those having an oesophagectomy (73.4%) or repair of unruptured AAA (82.3%). Mortality within 30 days of surgery ranged from 3.8% (excision of colon or rectum for cancer) to 13.4% (oesophagectomy).
Table 1 Characteristics of patients and hospitals for people who had one of five major surgical procedures in Ontario, Canada, between 1994 and 1999
Volume-outcome associations
Table 2 shows associations between volume and outcome for the five surgical procedures. In this table, the rows indicate the procedure of which the outcome is being assessed, and the columns indicate the procedure that was used to define hospital volume. For example, the first column of data in the first row represents the outcome of oesophagectomy according to the hospital volume of oesophagectomy. The second column of data in the first row represents the outcome of oesophagectomy according to the hospital volume of colorectal resection. Comparisons of operative mortality by hospital volume for the same procedure are indicated in bold along the diagonal.
Table 2 30 day mortality after each of five major surgical procedures according to hospital volume, by volume of same procedure and volume of other procedures
Association of outcome of procedure with volume of same procedure
Hospital volume and 30 day mortality were significantly associated for lung resection (adjusted odds ratio for death at high volume hospitals compared with low volume hospitals 0.64, 95% confidence interval 0.44 to 0.94) and AAA repair (0.62, 0.46 to 0.83). Although the point estimates of the association of volume and outcome for oesophagectomy (0.60, 0.30 to 1.20) and pancreaticoduodenectomy (0.76, 0.44 to 1.32) were consistent with an inverse relation between volume and outcome, the number of patients who had these procedures was relatively small and the confidence intervals included values consistent with no association. We found little evidence of an association between volume and outcome for colorectal resection (0.98, 0.83 to 1.16).
Association of outcome of procedure with volume of different procedure
We also examined the effect on operative mortality of the hospital volume of procedures other than the one for which the outcome was being measured. These comparisons are indicated by the non-bold data off the diagonal in table 2. In many instances, 30 day mortality was associated with the hospital volume of different procedures. This is illustrated by the fact that many of the off-diagonal odds ratio estimates are less than 1.0, indicating improved outcome in high volume hospitals regardless of the procedure for which a hospital was "high volume." For example, the reduction in 30 day mortality after pancreaticoduodenectomy in hospitals that were high volume hospitals for AAA repair (odds ratio 0.75, 0.45 to 1.27) was similar to the reduction in 30 day mortality after pancreaticoduodenectomy in hospitals that were high volume hospitals for pancreaticoduodenectomy (0.76, 0.44 to 1.32).
The association with the volume of a different procedure was occasionally stronger than with that of the same procedure. For example, the reduction in 30 day mortality after pancreaticoduodenectomy in hospitals that were high volume hospitals for lung resection (0.36, 0.23 to 0.57) was much stronger than the reduction in 30 day mortality after pancreaticoduodenectomy in hospitals that were high volume hospitals for pancreaticoduodenectomy (0.76, 0.44 to 1.32; table 2).
Correlation of hospital procedure volumes
The correlation coefficients for hospital volume for the five procedures we studied ranged from 0.17 (oesophagectomy and colorectal resection) to 0.73 (oesophagectomy and lung resection).
Discussion
Halm EA, Lee C, Chassin MR. Is volume related to outcome in health care? A systematic review and methodologic critique of the literature. Ann Intern Med 2002;137: 511-20.
Birkmeyer JD, Siewers AE, Finlayson EVA, Stukel TA, Lucas FL, Batista I, et al. Hospital volume and surgical mortality in the United States. N Engl J Med 2002;346: 1128-37.
Begg CB, Cramer LD, Hoskins WJ, Brennan MF. Impact of hospital volume on operative mortality for major cancer surgery. JAMA 1998;280: 1747-51.
Birkmeyer JD. High-risk surgery—follow the crowd. JAMA 2000;283: 1191-3.
Epstein AM. Volume and outcome—it is time to move ahead. N Engl J Med 2002;346: 1161-4.
Flood AB, Scott WR, Ewy W. Does practice make perfect? Part I: the relation between hospital volume and outcomes for selected diagnostic categories. Med Care 1984;22: 98-114.
Flood AB, Scott WR, Ewy W. Does practice make perfect? Part II: the relation between volume and outcomes and other hospital characteristics. Med Care 1984;22: 115-25.
Luft HS, Hunt SS, Maerki SC. The volume-outcome relationship: practice-makes-perfect or selective-referral patterns? Health Serv Res 1987;22: 157-82.
Melton LJI. Selection bias in the referral of patients and the natural history of surgical conditions. Mayo Clin Proc 1985;60: 880-5.
Ballard DJ, Bryant SC, O'Brien PC, Smith DC, Pine MB, Cortese DA. Referral selection bias in the Medicare mortality prediction model: are centers of referral for Medicare beneficiaries necessarily centers of excellence? Health Serv Res 1994;28: 771-84.
Birkmeyer JD. Should we regionalize major surgery? Potential benefits and policy considerations. J Am Coll Surg 2000;190: 341-9.
Donabedian A. The methods and findings of quality assessment and monitoring: an illustrated analysis. Ann Arbor, MI: Health Administration Press, 1985.
Glasgow RE, Mulvihill SJ. Hospital volume influences outcome in patients undergoing pancreatic resection for cancer. West J Med 1996;165: 294-300.
Simunovic M, To T, Theriault M, Langer B. Relation between hospital surgical volume and outcome for pancreatic resection for neoplasm in a publicly funded health care system. CMAJ 1999;160: 643-8.
Birkmeyer JD, Finlayson SR, Tosteson AN, Sharp SM, Warshaw AL, Fisher, et al. Effect of hospital volume on in-hospital mortality with pancreaticoduodenectomy. Surgery 1999;125: 250-6.
Iron K, Goel V, Williams JI. Concordance with hospital discharge abstracts and physician claims for surgical procedures in Ontario. Toronto, Canada: Institute for Clinical Evaluative Sciences, 1995. (ICES Working Paper Series Report No 42.)
Urbach DR, Bell CM, Austin PC. Differences in operative mortality between high- and low-volume hospitals in Ontario for 5 major surgical procedures: estimating the number of lives potentially saved through regionalization. CMAJ 2003;168: 1409-14.
Charlson ME, Pompei P, Ales KL, MacKenzie CR. A new method of classifying prognostic comorbidity in longitudinal studies: development and validation. J Chron Dis 1987;40: 373-83.
Deyo RA, Cherkin DC, Ciol MA. Adapting a clinical comorbidity index for use with ICD-9-CM administrative databases. J Clin Epidemiol 1992;45: 613-9.
Burton P, Gurrin L, Sly P. Extending the simple linear regression model to account for correlated responses: an introduction to generalized estimating equations and multi-level mixed modelling. Stat Med 1998;17: 1261-91.
Localio AR, Berlin JA, Ten Have TR, Kimmel SE. Adjustments for center in multicenter studies: an overview. Ann Intern Med 2001;135: 112-23.
Iezzoni LI. Assessing quality using administrative data. Ann Intern Med 1997;127: 666-74.
Urbach DR, Bell CM. The effect of patient selection on comorbidity-adjusted operative mortality risk: implications for outcomes studies of surgical procedures. J Clin Epidemiol 2002;55: 381-5.
Urbach DR. Misclassification of hospital procedure volume in surgical outcomes studies. Surgery 2000;127: 238-9.(David R Urbach, assistant)
Correspondence to: D R Urbach david.urbach@uhn.on.ca
Abstract
Evidence that the short term outcomes of complex surgical procedures are better in hospitals that do high volumes of such procedures has prompted some authors to suggest that high risk surgery should be regionalised at high volume hospitals.1-5 Relatively little research has been done into the underlying mechanisms and the potential role of selection bias in surgical volume-outcome associations.6-10 Health policy measures advocating volume based regionalisation are, for the most part, predicated on the overwhelming empirical evidence of hospital volume-outcome associations.11 In general, policy initiatives have proposed that patients needing certain high risk surgical procedures should have them done in a hospital that performs a large volume of similar procedures.
The findings of volume-outcome studies are usually interpreted in the light of the conceptual framework of quality in health care proposed by Donabedian: structures, processes, and outcomes.12 High volume hospitals are assumed to have structural characteristics associated with better quality of care, and providers in these hospitals are thought to improve their processes of care through experience in providing complex care. Central to this framework is an implied linkage between the volume of a specific surgical procedure done in a hospital and the outcome of the same surgical procedure. The finding of improved outcome after pancreaticoduodenectomy in high volume hospitals has been uniformly attributed to the high volume of pancreaticoduodenectomy,3 13-15 not the volume of a different complex procedure, the volume of all complex procedures, or other hospital characteristics. Whether the volume-outcome association is unique to the combination of the volume and the outcome of the same procedure has never been tested. We sought to answer the question of whether the improved outcome observed in high volume hospitals was unique to the volume of the procedure of which the outcome is being assessed.
Methods
Patients and hospitals
During the five year study period, 31 632 patients had one of the five surgical procedures of interest (table 1). Patients undergoing oesophagectomy seemed to have the highest burden of comorbid illness (median Charlson score 4), whereas those having colorectal cancer resection or repair of an unruptured AAA had fewer comorbid conditions (median Charlson score 0). The largest preponderance of male patients was among those having an oesophagectomy (73.4%) or repair of unruptured AAA (82.3%). Mortality within 30 days of surgery ranged from 3.8% (excision of colon or rectum for cancer) to 13.4% (oesophagectomy).
Table 1 Characteristics of patients and hospitals for people who had one of five major surgical procedures in Ontario, Canada, between 1994 and 1999
Volume-outcome associations
Table 2 shows associations between volume and outcome for the five surgical procedures. In this table, the rows indicate the procedure of which the outcome is being assessed, and the columns indicate the procedure that was used to define hospital volume. For example, the first column of data in the first row represents the outcome of oesophagectomy according to the hospital volume of oesophagectomy. The second column of data in the first row represents the outcome of oesophagectomy according to the hospital volume of colorectal resection. Comparisons of operative mortality by hospital volume for the same procedure are indicated in bold along the diagonal.
Table 2 30 day mortality after each of five major surgical procedures according to hospital volume, by volume of same procedure and volume of other procedures
Association of outcome of procedure with volume of same procedure
Hospital volume and 30 day mortality were significantly associated for lung resection (adjusted odds ratio for death at high volume hospitals compared with low volume hospitals 0.64, 95% confidence interval 0.44 to 0.94) and AAA repair (0.62, 0.46 to 0.83). Although the point estimates of the association of volume and outcome for oesophagectomy (0.60, 0.30 to 1.20) and pancreaticoduodenectomy (0.76, 0.44 to 1.32) were consistent with an inverse relation between volume and outcome, the number of patients who had these procedures was relatively small and the confidence intervals included values consistent with no association. We found little evidence of an association between volume and outcome for colorectal resection (0.98, 0.83 to 1.16).
Association of outcome of procedure with volume of different procedure
We also examined the effect on operative mortality of the hospital volume of procedures other than the one for which the outcome was being measured. These comparisons are indicated by the non-bold data off the diagonal in table 2. In many instances, 30 day mortality was associated with the hospital volume of different procedures. This is illustrated by the fact that many of the off-diagonal odds ratio estimates are less than 1.0, indicating improved outcome in high volume hospitals regardless of the procedure for which a hospital was "high volume." For example, the reduction in 30 day mortality after pancreaticoduodenectomy in hospitals that were high volume hospitals for AAA repair (odds ratio 0.75, 0.45 to 1.27) was similar to the reduction in 30 day mortality after pancreaticoduodenectomy in hospitals that were high volume hospitals for pancreaticoduodenectomy (0.76, 0.44 to 1.32).
The association with the volume of a different procedure was occasionally stronger than with that of the same procedure. For example, the reduction in 30 day mortality after pancreaticoduodenectomy in hospitals that were high volume hospitals for lung resection (0.36, 0.23 to 0.57) was much stronger than the reduction in 30 day mortality after pancreaticoduodenectomy in hospitals that were high volume hospitals for pancreaticoduodenectomy (0.76, 0.44 to 1.32; table 2).
Correlation of hospital procedure volumes
The correlation coefficients for hospital volume for the five procedures we studied ranged from 0.17 (oesophagectomy and colorectal resection) to 0.73 (oesophagectomy and lung resection).
Discussion
Halm EA, Lee C, Chassin MR. Is volume related to outcome in health care? A systematic review and methodologic critique of the literature. Ann Intern Med 2002;137: 511-20.
Birkmeyer JD, Siewers AE, Finlayson EVA, Stukel TA, Lucas FL, Batista I, et al. Hospital volume and surgical mortality in the United States. N Engl J Med 2002;346: 1128-37.
Begg CB, Cramer LD, Hoskins WJ, Brennan MF. Impact of hospital volume on operative mortality for major cancer surgery. JAMA 1998;280: 1747-51.
Birkmeyer JD. High-risk surgery—follow the crowd. JAMA 2000;283: 1191-3.
Epstein AM. Volume and outcome—it is time to move ahead. N Engl J Med 2002;346: 1161-4.
Flood AB, Scott WR, Ewy W. Does practice make perfect? Part I: the relation between hospital volume and outcomes for selected diagnostic categories. Med Care 1984;22: 98-114.
Flood AB, Scott WR, Ewy W. Does practice make perfect? Part II: the relation between volume and outcomes and other hospital characteristics. Med Care 1984;22: 115-25.
Luft HS, Hunt SS, Maerki SC. The volume-outcome relationship: practice-makes-perfect or selective-referral patterns? Health Serv Res 1987;22: 157-82.
Melton LJI. Selection bias in the referral of patients and the natural history of surgical conditions. Mayo Clin Proc 1985;60: 880-5.
Ballard DJ, Bryant SC, O'Brien PC, Smith DC, Pine MB, Cortese DA. Referral selection bias in the Medicare mortality prediction model: are centers of referral for Medicare beneficiaries necessarily centers of excellence? Health Serv Res 1994;28: 771-84.
Birkmeyer JD. Should we regionalize major surgery? Potential benefits and policy considerations. J Am Coll Surg 2000;190: 341-9.
Donabedian A. The methods and findings of quality assessment and monitoring: an illustrated analysis. Ann Arbor, MI: Health Administration Press, 1985.
Glasgow RE, Mulvihill SJ. Hospital volume influences outcome in patients undergoing pancreatic resection for cancer. West J Med 1996;165: 294-300.
Simunovic M, To T, Theriault M, Langer B. Relation between hospital surgical volume and outcome for pancreatic resection for neoplasm in a publicly funded health care system. CMAJ 1999;160: 643-8.
Birkmeyer JD, Finlayson SR, Tosteson AN, Sharp SM, Warshaw AL, Fisher, et al. Effect of hospital volume on in-hospital mortality with pancreaticoduodenectomy. Surgery 1999;125: 250-6.
Iron K, Goel V, Williams JI. Concordance with hospital discharge abstracts and physician claims for surgical procedures in Ontario. Toronto, Canada: Institute for Clinical Evaluative Sciences, 1995. (ICES Working Paper Series Report No 42.)
Urbach DR, Bell CM, Austin PC. Differences in operative mortality between high- and low-volume hospitals in Ontario for 5 major surgical procedures: estimating the number of lives potentially saved through regionalization. CMAJ 2003;168: 1409-14.
Charlson ME, Pompei P, Ales KL, MacKenzie CR. A new method of classifying prognostic comorbidity in longitudinal studies: development and validation. J Chron Dis 1987;40: 373-83.
Deyo RA, Cherkin DC, Ciol MA. Adapting a clinical comorbidity index for use with ICD-9-CM administrative databases. J Clin Epidemiol 1992;45: 613-9.
Burton P, Gurrin L, Sly P. Extending the simple linear regression model to account for correlated responses: an introduction to generalized estimating equations and multi-level mixed modelling. Stat Med 1998;17: 1261-91.
Localio AR, Berlin JA, Ten Have TR, Kimmel SE. Adjustments for center in multicenter studies: an overview. Ann Intern Med 2001;135: 112-23.
Iezzoni LI. Assessing quality using administrative data. Ann Intern Med 1997;127: 666-74.
Urbach DR, Bell CM. The effect of patient selection on comorbidity-adjusted operative mortality risk: implications for outcomes studies of surgical procedures. J Clin Epidemiol 2002;55: 381-5.
Urbach DR. Misclassification of hospital procedure volume in surgical outcomes studies. Surgery 2000;127: 238-9.(David R Urbach, assistant)