The present study is a comprehensive review of contemporary outcomes for vascular surgery operations at teaching and non-teaching institutions. Moreover, these findings are the first to examine the effect of time of year of vascular surgery operations at U.S. academic medical centers. These results demonstrate that teaching hospital status has no effect on outcomes after accounting for confounding differences in patient risk factors and operations. Academic quarter and time of year of operation did not independently influence patient mortality following vascular surgical procedures, reflecting the absence of a new-trainee influence on patient outcomes. Moreover, this study demonstrates the performance of more complex, higher risk operations at teaching hospitals. Despite these differences, patients undergoing vascular operations at teaching hospitals accrued only slightly longer hospital lengths of stay compared to patients undergoing operations at non-teaching hospitals.
The influence of time of year of operation has been postulated as a potential explanation for variations in patient outcomes following both medical and surgical hospitalizations at academic centers. This effect has been investigated within various patient populations with mixed results.1-4, 9
In a large, multi-institutional cohort study of 20,254 patients undergoing various surgical operations as collected in the American College of Surgeons-National Surgical Quality Improvement Program (NSQIP), Englesbe and colleagues (2007) demonstrated an impressive 41% increase in the risk of mortality for operations performed during July and August.9
Similarly, Rich and colleagues (1993) demonstrated a similar pattern of outcomes among patients with non-surgical diseases.3
However, several other studies have failed to demonstrate such an effect on surgical outcomes,2-4
including cardiac surgery operations performed at teaching hospitals.1
In another study of over 300,000 Medicare beneficiaries, the authors concluded that the beginning of the academic year was a safe time to undergo major surgical operations, including coronary artery bypass grafting, elective abdominal aortic aneurysm repair, carotid endarterectomy, pancreatectomy, esophagectomy, coloectomy, and hip repair following fracture.2
Similarly, Bakeen and colleagues documented similar risk-adjusted outcomes for over 70,000 Veterans Affairs (VA) patients undergoing cardiac operations during early (July 1-August 31) and late (September 1-June 31) academic periods.1
These results are in agreement with those of the present study.
The findings of the present study extend the examination of resident work experience and the investigation of academic season to reflect contemporary trends at academic medical centers spanning current eighty-hour workweek restrictions for surgical trainees. In our analyses, we controlled for comorbidities and other confounders through the inclusion of over 45 patient, hospital and operation related factors, including vascular surgery teaching hospital status, in each of our predictive models. Importantly, the combined influence of academic quarter and hospital status was assessed through the inclusion of an interaction term between these two variables in each statistical model. Even after these adjustments, performance of operations during a given academic quarter at both teaching and vascular surgery hospitals was not associated with increased patient mortality. In addition, the present results revealed differences in resource utilization between those undergoing operations at TH versus NTH, demonstrating slightly longer median hospital lengths of stay (LOS) and higher median total costs for those undergoing operations at TH. These findings are not surprising given the performance of more complex operations at academic medical centers.
Discrepancies in types of operations performed at teaching and non-teaching hospitals may explain the differences observed. Patients undergoing operations at teaching hospitals more frequently underwent complex and higher risk operations, including open and endovascular AAA repairs and aortoiliac bypass operations. In the Dutch Randomized Endovascular Aneurysm Management (DREAM) trial, 30 day mortality rates for endovascular aneurysm repair (EVAR) were 1.2%, while those for open aneurysm repair (OAR) was 4.6%.14
A second trial from the United Kingdom demonstrated similar early perioperative mortality rates for both EVAR (1.7%) and OAR (4.7%).15
In our study, we observed similar trends, documenting a 12 fold increase in the odds of death for patients undergoing OAR, a 7.9 fold increase in the odds of death for those undergoing EVAR, and 3.9 fold increased risk of death for those undergoing aortoiliac bypass operations compared to carotid enderarterectmy. Alternatively, non-teaching hospitals more frequently performed carotid endarterectomies. As carotid endarterectomy is a commonly performed operation with low perioperative mortality rates of approximately 0.5%,16
the higher frequency of these operations at non-teaching hospitals was postulated to explain the lower mortality on univariate analysis at these institutions. However, after risk adjustment, these discrepancies did not translate into higher adjusted mortality at either teaching or vascular surgery hospitals upon testing the interaction between major vascular operation type and hospital type. In fact, we observed no significant differences in the adjusted odds of mortality when testing this important interaction. Similarly, a slightly higher incidence of non-elective (urgent/emergent) operations at academic centers may have contributed to higher rates of postoperative cardiopulmonary and procedure related complications and increased mortality. However, following risk adjustment, the contribution of these differences on outcomes was small.
This study has important clinical relevance as it provides a nationally representative and broadly generalizable sampling of an increasingly reported epidemiologic phenomenon to surgical outcomes literature. The existing medical and surgical literature is mixed regarding the true influence of seasonality at academic institutions. Our results also provide important insight into surgical subspecialty care. As surgical subspecialty care often requires more specialized postoperative management, we believe that the lack of differences in patient outcomes at the beginning of an academic year may have several potential explanations. First, these findings may represent the result of a higher level of supervision from more senior surgical trainees and attending surgeons. Next, the presence of more mid-level providers often present on subspecialty surgical services can maintain consistent postoperative care during the period of new trainees. Finally, much of the postoperative care is protocolized to avoid variation in postoperative care. Consequently, we believe our data dispels the notion that patient outcomes differ at teaching institutions during the early academic season.
Despite these interesting results, this study has several limitations and potential considerations that warrant further discussion. First, inherent selection bias must be considered due to its retrospective design; however, the strict methodology and randomization of the NIS database likely reduces this bias. Second, the potential for unrecognized miscoding of diagnostic, procedure, and complication codes must be considered. The NIS database designates hospitals as teaching hospitals if there is any ACGME-accredited residency program, regardless of specialty, and these designations serve as a potential source of confounding. Additionally, true perioperative mortality and morbidity rates may be underestimated as they may have occurred following the patient's discharge. In our analyses, we categorized the operative time of year into academic quarters as opposed to analyzing the data by individual operative months. While this approach has been reported in similar series, it may dilute reported outcomes that may otherwise be observed within individual operative month. Nevertheless, we believe that such stratification appropriately captures and reports variations in patient outcomes that they exist throughout the academic year. The potential for a mortality bias in the hospital length of stay analysis should be considered. However because the mortality rates are rather small in both study groups, and fairly similar, such a bias would likely not be large. The de-identified nature of this administrative database limits us to only comment on in-hospital, short-term outcomes. In addition, we are unable to include adjustments for other well-established surgical risk factors, such as low preoperative albumin levels or poor nutrition status, as they are not captured in the NIS databases. However, upon sensitivity analyses our statistical models proved resilient to the presence of a potentially unmeasured confounder.