|Home | About | Journals | Submit | Contact Us | Français|
To determine if the lower mortality often observed in teaching-intensive hospitals is due to lower complication rates or lower death rates after complications (failure-to-rescue), and whether the benefits at these hospitals accrue equally to white and black patients, since blacks receive a disproportionate share of their care at teaching-intensive hospitals.
A retrospective study of patient outcomes and teaching intensity using logistic regression models, with and without adjusting for hospital fixed and random effects.
30-day mortality, in-hospital complications and failure-to-rescue (“FTR”, the probability of death following complications).
3,270 acute care hospitals in the United States.
Medicare claims on general, orthopedic and vascular surgery admissions in the U.S. for 2000 – 2005 (N = 4,658,954 unique patients).
Combining all surgeries, compared to non-teaching hospitals, patients at very major teaching hospitals demonstrated a 15% lower odds of death (P<0.0001), no difference in complications, and a 15% lower odds of death after complications (FTR) (P<0.0001). These relative benefits associated with higher RB ratio were not experienced by black patients, for whom the odds of mortality and FTR are similar at teaching and non-teaching hospitals, a pattern that is significantly different from that of white patients (P<0.0001).
Survival after surgery is higher at hospitals with higher teaching intensity. Improved survival is due to lower mortality after complications (better FTR), and generally not due to fewer complications. However, this better survival and FTR at teaching intensive hospitals is seen for whites, not for blacks.
Outcomes are generally better in hospitals with higher teaching intensity,1–6 but it is unclear how this benefit is achieved. Lower risk-adjusted mortality at teaching hospitals might result from the prevention of some complications, prevention of death after a complication has occurred, both, or even one effect offsetting the other. While teaching hospitals are generally larger, have more advanced technology, greater volume, and better nurse staffing4, 7, 8 (attributes that may aid in both preventing complications and successfully treating complications), it is by no means clear whether all patients benefit equally from these attributes.
This study first examines surgical outcomes to determine whether differences in complication and failure-to-rescue (FTR) rates explain observed differences in mortality rates between more and less teaching intensive hospitals. As a measure of death after complications, FTR provides an important test of how well hospitals do in treating patients who develop complications.9–11 We then examine how race is associated with outcomes at hospitals with higher or lower teaching intensity, as black patients both comprise a disproportionate share of patients at teaching-intensive hospitals, and obtain a disproportionate share of their surgical care at more teaching-intensive hospitals.12, 13
A description of the data set and the selection/exclusion criteria have been previously reported in the “Resident Hours Study”,14 which examined all Medicare patients admitted to short-term general non-federal acute-care hospitals from July 1, 2000 to June 30, 2005 with principal procedure/DRG classification of general, orthopedic or vascular surgery. The initial sample included 6,610,766 surgical patients from 5,736 acute care hospitals within 50 states. After exclusions, a total sample of 4,658,594 patients from 3,270 hospitals was left.
Outcome measures were death within 30-days of hospital admission, in-hospital complications, and failure-to-rescue. A patient was considered to have developed a complication if any complication was noted in the index hospitalization based on an algorithm published previously using the 1999–2000 Medicare Provider Analysis and Treatment File (MEDPAR) and available in the electronic appendix.11 Failure-to-Rescue (FTR) was defined as a death following an in-hospital complication and has been described in detail in other publications.9–11, 15–19
The risk-adjustment approach used was developed by Elixhauser and colleagues at AHRQ.20–22 We used age, sex, and 27 comorbidities (excluding fluid and electrolyte disorders and coagulopathy) 21, 22 and added 37 interaction terms derived from previous models using a 180-day lookback for comorbidities.11,23–26 There were a total of 82 DRG/Principal Procedure groups10, 11. Racial assignments were based on self-reports. To simplify the presentation, we have sorted patients only by black and white race, other racial groups were coded as “other” and not reported in this analysis.
The number of residents per hospital was obtained from Medicare Cost Reports. The resident-to-bed (RB) ratio is defined as the ratio of (interns + residents)/average operating beds.4, 14, 27 and has been used in previous studies2, 5, 6, 14 to differentiate “very major” teaching (RB >0.6), from less teaching-intensive hospitals.
We test the robustness of our findings with both logit regression models fitted by SAS Logistic and hospital random effects in a hierarchical model using SAS GLIMMIX.28 To help illustrate the impact of race and teaching intensity on outcomes, we also utilized direct standardization.19, 29, 30 After fitting our models with race and RB ratio, we calculated the estimated probability of each outcome under four alternative assumptions: All patients were: (1) white and in a hospital with an RB ratio = 0.6; (2) white and RB ratio = 0; (3) black and RB ratio = 0.6, and (4) black and RB ratio = 0. In this way, we can better illustrate comparisons of outcome rates by race and teaching intensity adjusting for differences in the health of patients, based on the distribution of risk factors for the entire study population.
Table 1 describes the patient population. Blacks generally were younger but had more comorbidities than whites. Patients at more teaching intensive hospitals were younger and had fewer comorbidities. Blacks undergoing procedures at non-teaching hospitals (RB = 0) were somewhat older and had more comorbidities than blacks at teaching-intensive (RB > 0.6) hospitals.
In Table 2 we display the associations between the RB ratio and other hospital characteristics often associated with better patient outcomes.1–4, 11, 17, 18 Larger RB ratios were associated with higher proportions of hospitals with characteristics traditionally associated with better outcomes. In this report, we use the RB ratio as a marker for a type of hospital, that is, as a proxy for the hospital characteristics associated with teaching intensity. Our models do not determine whether residents themselves cause the differences we observe.
For each outcome measure in Table 3 we provide results for each surgical category separately and then for the combined group. There were 4,658,954 patients in the mortality and complication models, but only 2,021,314 in the FTR model because the FTR analysis included only those who had a complication or died. For patients with similar comorbidities and procedures at hospitals with high teaching intensity (RB = 0.6 residents per bed) versus no residents (RB = 0), the fitted odds of death was 15% lower (95% CI = 13% to 16%) for the combined surgery group, with similar findings for subgroups. Results fitting a random effects model using individual hospital indicators were similar. Adding income (as defined by median income in the patient’s ZIP code31) to the combined surgery random effects model did not change these results, suggesting that the observed differences between teaching intensive and non-teaching hospitals are not reflecting unequal access by income level.
In contrast, the associations between the RB ratio and complication rates indicated no consistent relationship with odds ratios overlapping 1.0. However, similar to mortality, FTR rates were consistently lower in hospitals with higher RB ratios. Hospitals of high teaching intensity (RB = 0.6) compared to non-teaching hospitals (RB = 0) were associated with 14% (12% to 15%) lower odds of FTR for combined surgery, and again similar for subgroup analysis. The random effects model also produced similar results.
In Table 4 we can see that blacks had higher mortality rates and higher complication rates than whites. Whites displayed a lower odds of death at teaching intensive hospitals versus non-teaching hospitals (OR = 0.92, 95% CI = 0.90, 0.95) whereas blacks displayed a slightly increased, but statistically insignificant odds of dying at the teaching intensive versus non-teaching hospital (OR= 1.03, 95% CI =0.97, 1.09). For both whites and blacks there was a modest reduction in complications at the teaching intensive hospitals. Finally, whereas whites displayed a reduction in FTR rates in the teaching intensive hospitals versus the non-teaching hospitals (OR=0.94, (95% CI 0.92, 0.97), blacks displayed an increased FTR rate (OR=1.06, 95% CI = 1.00, 1.12). Figure 1 displays the unadjusted results. For both blacks and whites, rates of death were lower in the higher teaching intensity hospitals than in the non-teaching hospitals, although differences for blacks were far smaller than for whites when comparing non-teaching to teaching-intensive hospitals. We compared the relative advantage of teaching intensity for blacks by calculating the odds of an outcome between the higher (RB > 0.6) and lower (RB = 0) teaching intensity hospitals for blacks versus whites. The relative benefit (if less than 1) or worsening (if greater than 1) for blacks versus whites at teaching intensive versus non-teaching hospitals was 1.12 (1.05, 1.19), P < 0.0007 for death, 0.99 (0.96, 1.02), P=0.50 for complications and 1.12 (1.06, 1.20), P < 0.0004 for FTR.
Model 1 in Table 5 includes RB ratio and race and their interactions. In Model 1, in the first row of Table 5, the mortality model tests whether the odds of dying for blacks were higher or lower than for whites in hospitals without residents (RB ratio = 0). The adjusted odds of dying was 0.96 (0.95, 0.98) for blacks compared to whites at non-teaching hospitals (RB = 0). We then compared the odds of dying in a highly teaching intensive hospital (RB ratio = 0.6) to a hospital with an RB ratio = 0. For combined surgery, for whites, the odds of dying were 0.83 (0.81 to 0.84) representing 17% (16% to 19%) lower mortality in hospitals with an RB ratio of 0.6 versus 0. However, blacks displayed an odds ratio of 1.04 (0.99, 1.08) comparing hospitals with RB = 0.6 to RB = 0 hospitals. Hence, the mortality differences associated with teaching hospitals differ substantially for white and black patients -- 17% lower for whites and 4% higher for blacks when compared to non-teaching hospitals. The ratio 1.04/0.83 of these odds ratios (i.e., the race x RB interaction) is 1.25 (1.20 to 1.31) and represents the relative benefit (if < 1) or worsening (in > 1) in blacks relative to whites when comparing non-teaching hospitals (RB = 0) to teaching intensive hospitals (RB =0.6), (see Model 2 of Table 5). When we adjusted for Medicare geographic region in these models, our results were unchanged (results not shown).
The next analysis compares blacks and whites in the same hospital, in contrast to comparing blacks and whites at different hospitals with the same resident-to-bed ratio. We fit a model in which the RB ratio was replaced by hospital indicators or fixed effects, so RB ratio appears in the model only in the interaction with race. As can be seen from the row of Table 5 labeled “Hospital Fixed Effects”, in this alternative model (Model 3), the overall ratio of the black to white odds ratios comparing RB = 0.6 to RB = 0 is still large, but somewhat smaller, namely 1.13 (1.07 to 1.19), P < 0.0001 in the fixed effects model. This suggests that even after controlling for the individual hospital, blacks benefit less than whites when comparing highly teaching intensive and non-teaching hospitals. The random effects model specifying each hospital with an indicator variable (Model 4 in Table 5) gave similar results for the RB*black interaction, with the odds ratio for death being 1.18 (1.12 to 1.24).
Complications displayed a very different pattern. Among patients in the combined surgery group, at non-teaching hospitals (RB = 0), blacks had a 14% (13% to 15%) higher odds of developing a complication than whites. Whites in highly teaching intensive hospitals (RB = 0.6) had no different odds of complications than whites in non-teaching hospitals (OR= 1.0, (0.99, 1.00). Similarly, for blacks, the odds of developing complications were not different: OR = 0.99 (0.97, 1.01) and not significant when comparing hospitals with an RB ratio of 0.6 versus 0. The two models with fixed or random hospital indicators yield the same conclusion.
Failure-to-rescue results are reported in the last column of Table 5, and are generally similar in pattern to the mortality results. Whites, but not blacks, had lower FTR rates at teaching hospitals compared to non-teaching hospitals.
To better display the associations noted in Table 5, the directly standardized rates of death, complication and FTR are displayed in Figure 2 for each of 4 hypothetical (or ‘standardized’) patient groups: a black or white patient in a hospital with an RB ratio of 0.6 or 0. In terms of mortality and FTR, whites do better at teaching hospitals than non-teaching hospitals, but blacks do about the same at teaching and non-teaching hospitals. While complication rates were higher in blacks than whites, RB ratio had little association with whether whites or blacks developed complications. However, whereas whites were more likely to survive after experiencing a complication at a teaching intensive hospital as compared to a hospital without residents, this was not the case for black patients.
We found, as have others,1, 3, 11, 32, 33 that hospitals with higher teaching intensity appear to have lower risk-adjusted mortality after major surgery than less teaching intensive hospitals. Previous studies have shown similar or higher postoperative complication rates at teaching hospitals than at non-teaching hospitals.34–38 We now demonstrate that the lower mortality rates in surgical cases are mediated by fewer deaths among patients who experienced complications (lower FTR) and not by lower rates of complications. Moreover, this finding does not change when adjustments are made for ZIP code level income, suggesting that lower FTR rates in this population are not generated by unequal access to higher teaching intensity hospitals by patients of different incomes.
It is therefore of interest to find, when using data from the entire Medicare population in the United States, that blacks, unlike whites, do not experience lower surgical mortality and FTR rates at teaching intensive hospitals. It appears that blacks fare about equally well in teaching and non-teaching hospitals, whereas whites have significantly better risk adjusted mortality and FTR at teaching hospitals than at non-teaching hospitals.
Why does this racial disparity in mortality and FTR exist? It is noteworthy that this disparity is smaller, though still substantial, in the model with a separate fixed effect for each hospital. This indicates that some, but by no means all, of the disparity stems from blacks going to teaching hospitals with similar RB ratios but worse mortality and FTR rates than their white counterparts (a similar effect was reported by Lucas et al.39 and Barnato et al.40). However, our study found that the within-hospital disparities are large, significant, and more substantial than those observed in previous work.13, 40–42
In earlier work we also have studied racial differences in the length of surgery for comparable procedures, and found lower income black Medicare patients had surgery that took on average 29 minutes longer than whites of similar income (P < 0.0001). In part this was because blacks tended to go to teaching hospitals that had longer procedure times.43, 44 However, even when adjusting for the individual hospital, procedure time remained significantly longer in blacks, but now by 7 minutes (P < 0.0001). Inside some very major teaching hospitals the black-white difference was not apparent, while in others the difference was more than 16 minutes for comparable surgery. The observed racial disparities in adjusted procedure length raises questions as to whether there are potential differences in who provides care to these populations at teaching-intensive hospitals.
Why racial differences in FTR should occur within hospitals is not well understood, but there are many possibilities. Chan et al.45 report that black patients were 22% (P < 0.009) more likely to experience a delay in initiating defibrillation than their white counterparts, with arrests occurring in unmonitored beds more often than whites (P < 0.001). Are black patients being monitored in the same way as their white counterparts? In search of a more general cause, Balsa and McGuire have described a process of “statistical” discrimination in which unintentional actions potentially based on poor communication may lead to disparities in outcomes. 46 This could be exacerbated in time-pressured environments in which relatively inexperienced providers deliver much of the care. Unintentional differences in communication47 might lead to less appropriate or less accurate monitoring of black patients, or less involvement in their care by personnel who could make a difference in reducing FTR. In our previous work we considered the possibility that the differences in surgical procedure length between whites and blacks may be due to different levels of involvement of physicians-in-training in black versus white patients.43, 44
How does the difference in income between blacks and whites relate to the disparity in FTR? This is a complex issue because these are Medicare, non HMO, patients and, in principle, income should not be a factor in care, though gaps between principle and practice might occur. We did adjust for median income within the ZIP code of residence, and after adjustment, teaching intensive hospitals still have lower FTR than non-teaching hospitals in whites but not blacks, suggesting that the apparent benefit of teaching intensity is not an artifact of unequal income.
It also was interesting to observe that at non-teaching hospitals, blacks actually had slightly lower overall adjusted mortality than whites, although the crude mortality rates were higher for blacks than whites in non-teaching hospitals.48–51 We would not want to make too much of our finding since the coefficient on the race difference in non-teaching hospitals was small (an odds ratio of 0.96) and recent work by Volpp et al.49 and Polsky et al.,50 report that black patients were noted to have lower 30-day mortality than whites for a number of conditions, but this reversed with longer follow-up.
It is important to note limitations to our study. Although we report on a very large sample size based on Medicare claims data, the tradeoff is that these records do not contain chart-based data. For example, we do not have details on the sequencing or severity of complications and do not know whether subgroups in this study had a different distribution of complications that may partially explain our findings.52, 53 Relying on claims data, and not chart review, does leave open the possibility that racial differences in mortality and failure-to-rescue may be due to unmeasured severity. However, it should be noted that our study compared whites at less teaching-intensive hospitals to whites at more teaching-intensive hospitals, and the same for blacks. Hence, for our severity adjustment to be inadequate it would need to be the case that even after our extensive risk adjustment, whites entering teaching hospitals are in better health than whites entering non-teaching hospitals, but blacks entering teaching hospitals are in the same health as blacks entering non-teaching hospitals. If blacks were sicker than whites in the same unmeasured ways upon admission to all hospitals, this by itself would not produce the pattern of mortality and FTR rates that we found.
In conclusion, teaching intensive hospitals with high RB ratios have lower risk adjusted mortality rates after major surgery than hospitals with lower ratios or without residents. This better survival is mainly due to better failure-to-rescue rates after postoperative complications. However, on average, while whites have lower mortality and failure-to-rescue rates at teaching intensive hospitals, blacks do not.
This work was funded through The National Heart, Lung, and Blood Institute grant # R01 HL082637, The Department of Veterans Affairs grant # IIR 04-202, and The National Science Foundation grant # SES 0646002. There are no known financial conflicts of interest among any of the authors including but not limited to employment/affiliation, all grants or funding, honoraria, paid consultancies, expert testimony, stock ownership or options, and patents filed, received or pending. Drs. Silber and Volpp had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. The sponsors/funders have had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript. Drs. Silber, Rosenbaum and Volpp were responsible for the conceptualization and design of the statistical models and Ms. Wang is responsible for the SAS programming performed for this study. We thank Laura J. Bressler, BA, and Traci Frank, Center for Outcomes Research, The Children’s Hospital of Philadelphia, Philadelphia, PA for their help in conducting this research.