ORIGINAL ARTICLE

Relationship Between Patient-reported Outcomes of Elective Surgery and Hospital and Consultant Volume Mira Varagunam, PhD, Andrew Hutchings, MSc, and Nick Black, MD

Objective: Our aim was to analyze the relationship for 3 elective operations between outcome [patient-reported outcome measures (PROMs) for functional status, health-related quality of life, and postoperative complications] and both hospital and consultant volume. Methods: Hospitals (NHS and independent) and consultants undertaking at least 10 NHS-funded procedures during 2011/2012 were included (230 hospitals for hip and knee replacement, 257 for hernia repair; 978 consultants for hip replacement, 1172 for knee replacement, and 1288 for hernia repair). Outcomes (disease-specific and generic PROMs, patient-reported complications) were available from the NHS National PROMs Programme for 2009/ 2010 to 2011/2012. Relationship between case-mix adjusted outcomes and volume investigated using multilevel modeling. Results: There was considerable variation in hospital volumes (about 10-fold) and consultant volumes (about 5-fold). No significant association was observed between hospital volume and outcome for all 3 procedures. For consultant volume, there was no significant association for knee replacement or hernia repair. However, outcomes were statistically significantly better for hip replacement, although the effect was of little clinical significance: an additional 10 cases was associated with a higher Oxford Hip Score (0.06), higher EQ-5D score (0.001), and lower odds ratio of complications (0.992). Conclusions: There are unlikely to be any benefits to patients from centralization of elective surgery into higher volume hospitals as regards the effectiveness of surgery or the avoidance of minor complications. There is some evidence that very low volume consultants achieve poorer outcomes than higher volume colleagues but the difference is slight and of little or no clinical significance. Key Words: patient-reported outcomes, elective surgery, hospital volume, consultant volume (Med Care 2015;53: 310–316)

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here is increasing interest among policymakers and health care funders to reduce the number of acute hospitals that manage emergency referrals and admissions. This

From the Department of Health Services Research & Policy, London School of Hygiene & Tropical Medicine, London, UK. The authors declare no conflict of interest. Reprints: Nick Black, MD, Department of Health Services Research & Policy, London School of Hygiene & Tropical Medicine, 15-17 Tavistock Place, London WC1H 9SH, UK. E-mail: [email protected]. Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved. ISSN: 0025-7079/15/5303-0310

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is largely driven by the challenge of providing experienced consultants (fully trained doctors) throughout the day and night, 7 days a week. Although such a consideration may reduce the number of hospitals providing emergency care, staffing concerns are less relevant when considering arrangements for elective admissions, particularly in surgery, when 24/7 working is not a necessity. However, it has been suggested that high-volume providers of elective care may have higher efficiency as a result both of lower costs through economies of scale and from better outcomes. To date, studies of the volume-outcome relationship in elective surgery have focused on adverse outcomes such as postoperative mortality and complications.1,2 It has been recognized for over 20 years that hospitals that perform a larger volume of surgery and surgeons who carry out a larger volume of operations, generally achieve lower mortality.3,4 Higher consultant volume has also been shown to be associated with fewer serious complications, revision operations, and infections.5–12 There have, however, been some studies that have found no such associations.13,14 One limitation of the studies that focus on postoperative mortality is that this is a rare event for most elective operations. For example, 90-day mortality in the United Kingdom following hip replacement surgery is 0.3%15 and 0.4% for knee replacement.16 In addition, most of the literature focuses on the safety of care (postoperative mortality, complications) rather than on the effectiveness of care, that is, the benefits of surgery such as changes in functional status and quality of life (HRQL). The few studies of joint replacement surgery that considered patients’ functional status have found better outcome with higher volume for total knee replacement17,18 but no association for total hip replacement.19 The dearth of studies of volume and effectiveness (health gain from surgery) is not surprising, given the absence of available routine data on the latter. The advent of the National Patient Reported Outcome Measures (PROMs) program in 2009 in England to measure the functional status and quality of life of all NHS-funded patients undergoing hip replacement, knee replacement, and hernia repair provides a new, welcome opportunity to investigate the effect of hospital and consultant volume on outcome.20 The program provides measures of functional status and HRQL using continuous scales, which have the potential to detect small but important differences in outcomes, hence providing a more sensitive indicator than a categorical variable such as mortality. In addition, data on patient-reported postoperative complications are also available. Our aim was to analyze the relationship for 3 elective operations between outcome (patient reported functional Medical Care



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status, HRQL, and postoperative complications) and both hospital and consultant volume.

METHODS Data All patients undergoing NHS-funded hip replacement, knee replacement, and groin hernia repair between April 2009 and March 2012 were invited to complete a preoperative questionnaire, which included disease-specific and generic PROMs. Follow-up questionnaires, mailed to patients 3 (hernia repair) or 6 (hip and knee replacement) months after surgery, included the same PROMs and a question about the occurrence of 4 common complications (wound problems; urinary problems; allergy or reaction to drug; bleeding). The length of follow-up was a pragmatic compromise between clinical considerations (time to achieve full benefit from the procedure) and the needs for timely feedback of outcome data to providers and patients with the aim of improving the quality of care. Completed questionnaires were linked, by the NHS Health and Social Care Information Centre, to the patient’s episode in the hospital administrative database—Hospital Episode Statistics (HES). This provided information on the patient’s ethnicity and enabled us to assign their socioeconomic status, derived from their postcode and based on the Index of Multiple Deprivation.21 In addition, HES identified the patient’s consultant and the hospital where the operation was performed. The effectiveness of hip and knee replacement was assessed using a disease-specific PROM—the Oxford Hip Score (OHS)22 and the Oxford Knee Score (OKS).23 Both include 12 items, each scored from 0 to 4 and summed to provide an overall score of between 0 (severe symptoms and disability) and 48 (no problem). There was no disease-specific PROM available for hernia repair. All 3 procedures were also assessed using a generic PROM, the EQ-5D-3L, which assesses 5 dimensions of health (mobility, self-care, daily activities, pain, and anxiety/depression).24 Each question has 3 levels of response and answers are transformed into a HRQL score using utilities from the UKTime Trade-Off value set.25 Scores range from –0.59 (worse than death) through 0.00 (dead) to 1.00 (perfect health). The measurement properties of all the PROMs used had been reviewed and established before their selection for use.26 Finally, the safety of all 3 procedures was assessed as the proportion of patients reporting at least 1 of 4 common complications. The proportions of patients reporting a complication were: 30% for hip replacement; 32% knee replacement; and 23% hernia repair.27 The recruitment rates for the 3 procedures were 69% for hip replacement, 67% for knee replacement, and 46% for hernia repair. Postoperative response rates were 85%, 85%, and 75%, respectively.

Inclusion Criteria We restricted our analysis to hospitals and consultants who had at least 10 cases recorded in HES in 2011/2012 and at Copyright

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Elective Surgery and Hospital and Consultant Volume

least 10 cases with complete PROMs data (those with missing items were excluded) during the period 2009/2010 to 2011/ 2012 (as long as some data were available for each year). The reason was to ensure that occasional cases that were incorrectly attributed to a nonsurgical consultant were excluded. Primary and revision procedures were included. A “complete case” analysis was conducted (ie, a case was excluded if 1 item was missing). There was 1 exception to this. The OHS and OKS tolerate up to 20% missing items with a value for missing item being imputed on the basis of the values for the items completed. This resulted in 168 NHS and 62 independent (private) providers for hip and knee replacement and 197 NHS and 60 independent providers for hernia repair. The numbers of consultants included were 978 for hip replacement, 1172 for knee replacement, and 1288 for hernia repair.

Case-mix Adjustment We adjusted for patients’ age, sex, socioeconomic status (as quintiles of the Index of Multiple Deprivation), self-reported comorbidities (heart disease; hypertension; stroke; claudication; lung disease; diabetes; kidney disease; neurological diseases; liver disease; cancer; depression), having had undergone previous surgery on the same hip or knee (for those operations) and preoperative PROM scores. The last of these is known to be the most predictive factor.28

Statistical Analysis Multilevel modeling was performed to analyze the relationship between volume and outcome with the exposure defined as HES volume for the year 2011/2012 for the hospitals and consultants. All analyses were performed on RunMLWin (University of Bristol). Case-mix adjusted multilevel models29 with a random intercept for the hospital and consultant to control for differences in hospitals (such as nursing quality) and differences in consultants (such as surgical technique and skills) were run with hospital volume and consultant volume as a fixed effect. The associations of consultant and hospital volume with outcome were estimated from the same 3-level model. Model assumptions were checked by examining residuals excluding potentially influential consultants and adding quadratic terms for volume to check for nonlinear associations. The association between volume and complications was analyzed using random effect logit models. Case-mix adjusted models were run with a random intercept for hospital and consultant with hospital volume and consultant volume added as fixed effects.

RESULTS Distribution of Hospital and Consultant Volumes The annual volume of cases varied considerably by hospital and by consultant (Table 1). There was about a 10-fold variation for hospitals, with about 10% undertaking < 50 and 10% more than 500 a year. Variation in consultant volumes was less extreme with about half undertaking 250 a year. www.lww-medicalcare.com |

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TABLE 1. Distribution of Numbers (%) of Hospitals and Surgeons by Annual Volumes (2011/2012) N (%) Hospitals Volume 10-50 51-100 101-250 251-500 > 500 Total

Hip Replacement 21 39 71 76 23 230

(9.1) (17.0) (30.9) (33.0) (10.0) (100)

Knee Replacement 19 33 75 78 25 230

Consultants Groin Hernia Repair

(8.3) (14.4) (32.6) (33.9) (10.9) (100)

15 41 95 89 17 237

Hip Replacement

(5.8) (16.0) (37.0) (34.6) (6.6) (100)

Association Between Hospital Volume and Outcome Outcomes for 79,050 patients having hip replacements, 83,648 having knee replacements, and 44,140 having groin hernia surgery were analyzed (Table 2). Figure 1 shows the lack of association between hospital volume and unadjusted postoperative PROM scores. After adjustment for case-mix there was still no statistically significant association for change in disease-specific or generic PROM for any of the 3 procedures (Table 3). A difference in hospital volume of 100 cases was not associated with any difference in the amount of health gain in terms of functional status or HRQL. The same was true when complications were considered. There was no statistically significant association between hospital volume and the odds ratio (OR) of developing a complication: hip replacement OR [95% confidence interval(CI)] 0.989 (0.976, 1.001), P = 0.078; knee replacement OR 0.994 (0.983, 1.005), P = 0.268; and groin hernia repair OR 1.010 (0.991, 1.029), P = 0.299.

506 280 188 4 0 978

(51.7) (28.6) (19.2) (0.4) (0) (100)

621 402 146 3 0 1172

(53.0) (34.3) (12.5) (0.3) (0) (100)

Groin Hernia Repair 850 338 95 5 0 1288

(66.0) (26.2) (7.4) (0.4) (0) (100)

association for hip replacement both for disease-specific and generic PROMs (Table 4). Consultants undertaking 10 more cases was associated with patients reporting slightly greater improvement according to the Oxford Hip Score (0.06) and the EQ-5D (0.001). In contrast, there was no significant association for the other 2 procedures. There was also a statistically significant association between consultant volume and the likelihood of developing a complication for hip replacement surgery OR (95% CI) 0.993 (0.989, 0.996), P < 0.001. Again there was no significant association for the other 2 procedures: knee replacement surgery OR 0.998 (0.993, 1.002), P = 0.264; and groin hernia repair OR 1.001 (0.995, 1.006), P = 0.794. The examination of residuals and the lack of significant improvement in model fit by including volume as a quadratic term indicated that there was little evidence to support a nonlinear association between volume and outcome. The exclusion of 2 potentially influential high-volume consultants did not alter the results of the hip replacement analyses.

Association Between Consultant Volume and Outcome Figure 2 shows the association between consultant volume and unadjusted postoperative PROMs scores. After adjustment for case-mix, there was a statistically significant

Knee Replacement

DISCUSSION Main Findings There was no significant association between hospital volume and the outcome of surgery as regards effectiveness

TABLE 2. Characteristics of Patients by Procedure Hip Replacement (n = 79,050) Mean age (SD) Female [n (%)] Comorbidity [n (%)] Heart disease Hypertension Stroke Claudication Lung disease Diabetes Kidney disease Neurological disease Liver disease Cancer Depression Revision operation [n (%)] Mean disease specific preoperative PROM score (SD) Mean EQ-5D preoperative PROM score (SD)

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Knee Replacement (n = 83,648)

68 (11) 47 239 (60)

69 (9) 47 347 (57)

7824 31 393 1114 5207 5265 6598 1339 615 387 3639 5631 8127 18 0.35

9269 (11) 38 635 (46) 1431 (2) 7065(8) 6067 (7) 10 435 (12) 1477 (2) 765 (1) 423 (0.5) 3595 (4) 6677 (8) 6548 (8) 18.7 (7.8) 0.40 (0.31)

(10) (40) (1) (7) (7) (9) (2) (1) (0.5) (5) (7) (10) (8.4) (0.32)

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Groin Hernia Repair (n = 44,140) 62 (15) 3132 (7) 4362 (10) 12 432 (28) 672 (2) 1999 (5) 2955 (7) 2361 (5) 593 (1) 429 (1) 211 (0.5) 2020 (5) 1844 (4) NA NA 0.79 (0.20)

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Elective Surgery and Hospital and Consultant Volume

0

500

1000

40 35 30 25

35

40

Mean post-operative OKS

45

45

Knee Replacement

30

Mean post-operative OHS

Hip Replacement

1500

0

500

Hospital volume

1000

1500

Hospital volume

.95 .9 .85 .8 .75 .7

Mean post-operative EQ5D

Hernia Repair

0

200

400 600 Hospital volume

800

1000

FIGURE 1. Association between hospital volume and unadjusted postoperative PROM score.

(functional status and HRQL) and safety (postoperative complications) for all 3 procedures studied. There was also no association with consultant volume for knee replacement and groin hernia surgery. In contrast, there was a statistically significant association between consultant volume and outcome for hip replacement surgery. Higher consultant volume was associated with slightly greater gain in functional status (change in OHS was 0.06 greater) and HRQL (change in EQ5D was 0.001 greater) for each additional 10 cases. In addition, there was less risk of a postoperative complication (OR 0.992).

Relationship to Previous Research Our failure to find an association between volume and outcome for total knee replacement is not consistent with the 2 previous studies reported. Heck et al17 found that functional status improved more in hospitals with at least 50 cases a year, although there was no association with consultant volume. However, this small study may have been subject to bias as the 48 surgeons who took part selected the 291 patients to participate, an average of only 6 each. The other study, which was methodologically strong, reported an association for both hospital and consultant volume.18 This may have been because they included very low volume hospitals and consultants, the types of providers for which the greatest concern exists. Copyright

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The only previous study of total hip replacement19 found no association with volume in contrast to our finding that higher consultant volume (but not higher hospital volume) was associated with better outcomes. The difference may be due to the time at which outcome was assessed. The earlier study assessed outcome 3 years after surgery, whereas in our study it was after only 6 months. Any difference in outcome may decay over time.

What This Study Adds Our results indicate that hospital volume is not associated with the outcome of surgery when judged by patients’ reports of changes to their functional status or HRQL for all 3 procedures. In contrast, consultant volume has an effect in hip replacement on all 3 outcomes studied. A patient operated on by a consultant with an annual volume of 250 may achieve 1.2 points more on the OHS scale compared with patients treated by a consultant with a caseload of 50. To put this in context, a clinically minimal important difference for the OHS is reported as being about 4 points.30

Limitations There are 5 potential limitations to consider. First, not all patients were recruited to the PROMs Programme and not all those who completed a preoperative questionnaire responded to the postoperative questionnaire. Previous work has indicated www.lww-medicalcare.com |

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TABLE 3. Association Between Hospital Volume and Health Gain (Disease-specific and Generic PROMs) Change in Adjusted Postoperative PROM (95% CIs) Associated With Additional 100 Cases Procedures

P

Disease Specific

Hip replacement Knee replacement Groin hernia repair

0.015 ( 0.077, 0.048) 0.014 ( 0.080, 0.051)

Generic

0.645 0.673

that while recruitment bias exists, it is taken into account when adjusting for patient characteristics in the analysis.31 Postoperative response bias also occurs but has been shown to be slight.32 It is, therefore, not apparent that nonrecruitment or nonresponse will have introduced any serious biases. Second, for the consultant analysis, our estimates of consultant volume did not include the operations they performed for privately funded procedures. In some areas of England (eg, London and the south east) that would have underestimated their true volume of work. As data on privately funded operations by consultant are not publicly available, it is impossible to determine what effect the omission of privately funded surgery had on the consultantlevel analysis as the relationship between a consultant’s NHS volume and their private volume is not uniform.

0.0010 ( 0.0025, 0.0004) 0.0009 ( 0.0024, 0.0007) 0.0004 ( 0.0006, 0.0015)

0.169 0.263 0.405

Third, a consultant’s volume referred to the number of patients for which they were clinically responsible. In many instances, the consultant will not have been the operating surgeon, although they may have been present and supervising a trainee surgeon. It is possible that the proportion of cases in which the responsible consultant is also the operating surgeon varies by consultant volume. For example, high-volume consultants may be more likely to be involved in training juniors than low-volume consultants. Accurate data were not available to determine who the operating surgeon was so the analyses relate to “responsibility volumes” rather than “operation volumes.” Fourth, some apparently low-volume consultants may not have been working throughout 2011/2012, the year on which their volume was based, as they may have been Knee Replacement

40 30 20 10

25

30

35

40

45

Mean post-operative OKS

50

50

Hip Replacement

Mean post-operative OHS

P

0

100

200 300 Consultant volume

400

0

100

200 300 Consultant volume

400

.9 .85 .8 .75

Mean post-operative EQ5D

.95

Hernia Repair

0

100

200 300 Consultant volume

400

FIGURE 2. Association between consultant volume and unadjusted postoperative PROM score.

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TABLE 4. Association Between Consultant Volume and Health Gain (Disease-specific and Generic PROMs) Change in Postoperative PROM (95% CIs) Associated With Additional 10 Cases Procedure Hip replacement Knee replacement Groin hernia repair

Disease Specific

P

Generic

P

0.058 (0.040, 0.075) 0.001 ( 0.020, 0.023)

< 0.001 0.893

0.0012 (0.0008, 0.0016) 0.0003 ( 0.0002, 0.0008) 0.0002 ( 0.0002, 0.0005)

< 0.001 0.267 0.383

appointed or retired during the year. The small proportion of consultants involved is unlikely to have been sufficient to undermine the results. Finally, we modeled outcomes using the postoperative PROM scores adjusted for preoperative scores in preference to analyzing unadjusted change scores (postoperative preoperative score) because of the presence of a ceiling effect.33 Reanalysis using unadjusted change scores (not reported) produced similar findings of a small and statistically significant positive association between higher consultant volume and greater improvement for hip replacements but no evidence of other associations between volume and outcome.

Implications of the Findings First, although reconfiguration of hospital services will, in all likelihood, be determined by factors such as surgical staffing requirements, travel distances for patients, economies of scale, and political considerations, this study suggests that there are unlikely to be any benefits to patients from centralization into higher volume hospitals as regards greater effectiveness of elective surgery or the avoidance of minor complications. It is possible that the incidence of severe harm (including death) is associated with volume, which might justify greater concentration and higher volumes. Second, there is some evidence that very low-volume consultants achieve poorer outcomes than higher volume colleagues but the difference is slight. Whether or not differences of little or no clinical significance should be taken into account in determining the configuration of surgical services is a factor that policy-makers need to consider. REFERENCES 1. Wilson A, Marlow NE, Maddern GJ, et al. Radical prostatectomy: a systematic review of the impact of hospital and surgeon volume on patient outcome. ANZ J Surg. 2010;80:24–29. 2. Hannan EL, Racz M, Ryan TJ, et al. Coronary angioplasty volumeoutcome relationships for hospitals and cardiologists. JAMA. 1997;277: 892–898. 3. Luft HS, Hunt SS, Maerki SC. The volume-outcome relationship: practice-makes-perfect or selective-referral patterns?. Health Serv Res. 1987;22:157–182. 4. Black N, Johnston A. Volume and outcome in hospital care: evidence, explanations and implications. Health Serv Manage Res. 1990;3:108–114. 5. Lavernia CJ, Guzman JF. Relationship of surgical volume to short-term mortality, morbidity, and hospital charges in arthroplasty. J Arthroplasty. 1995;10:133–140. 6. Kreder HJ, Deyo RA, Koepsell T, et al. Relationship between the volume of total hip replacements performed by providers and the rates of postoperative complications in the state of Washington. J Bone Joint Surg Am. 1997;79:485–494. 7. Katz JN, Losina E, Barrett J, et al. Association between hospital and surgeon procedure volume and outcomes of total hip replacement in the

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on a Review of the Scientific Evidence. London, UK: Health Services Research Unit, London School of Hygiene & Tropical Medicine; 2005. 27. Grosse Frie K, van der Meulen J, Black N. Relationship between patients’ reports of complications and symptoms, disability and quality of life after surgery. Brit J Surg. 2012;99:1156–1163. 28. Northgate Information SolutionsPROMs risk adjustment methodology guide for general surgery and orthopaedic procedures. September 2010. Available at: http://www.england.nhs.uk/statistics/wp-ontent/uploads/ sites/2/2013/07/proms-ris-adj-meth-sur-orth.pdf Accessed 25 September, 2014). 29. Neuburger J, Hutchings A, van der Meulen J, et al. Using patient reported outcomes (PROs) to compare the performance of providers: does the choice of measure matter?. Med Care. 2013;51:517–523.

30. Browne JP, van der Meulen JH, Lewsey JD, et al. Mathematical coupling may account for the association between baseline severity and minimally important difference value. J Clin Epidemiol. 2010;63:865–874. 31. Hutchings A, Neuburger J, van der Meulen J, et al. Estimating recruitment rates for routine use of patient reported outcome measures and the impact on provider comparisons. BMC Health Serv Res. 2014;14:66. 32. Hutchings A, Grosse Frie K, Neuburger J, et al. Late response to patientreported outcome questionnaires after surgery was associated with worse outcome. J Clin Epidemiol. 2013;66:218–225. 33. Neuberger J, Cromwell DA, Hutchings A, et al. Funnel plots for comparing provider performance based on patient-reported outcome measures. BMJ Qual Saf. 2011;20:1020–1026.

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Relationship between patient-reported outcomes of elective surgery and hospital and consultant volume.

Our aim was to analyze the relationship for 3 elective operations between outcome [patient-reported outcome measures (PROMs) for functional status, he...
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