Abstract
BackgroundThe purpose of this study is (1) to define the proportion of patients undergoing emergent open repair of thoracic aortic dissection admitted directly through the emergency room versus those transferred from outside hospitals and (2) to determine if a volume-outcomes relationship exists for those patients across admission types.MethodsDe-identified patient-level data was obtained from the Nationwide Inpatient Sample (2004–2008). Patients undergoing emergent aortic surgery for thoracic aortic dissection (n = 1,507) were identified by ICD-9 codes and stratified by annual center volume into low volume (≤5 cases/year) (n = 963; 63.9 %), intermediate volume (6–10 cases/year) (n = 370; 24.5 %), and high volume (≥11 cases/year) (n = 174; 11.6 %) groups. The analysis was further stratified by admission type: direct admission (DA), transfer admission (TA), and other. The primary outcome was in-hospital mortality. Multivariate logistic regression analysis was performed comparing outcomes between high vs low and high vs intermediate volume centers.ResultsOverall in-hospital mortality was 21.8 % (n = 328/1,507). Absolute percent mortality at high volume centers was significantly lower (12.6 %) than at medium (20.6 %) and low volume (23.9 %) centers. For DA patients, mortality was 10.6, 21.4, and 24.0 % for high, medium, and low volume centers respectively. For TA patients, mortality was 10.2, 12.7, and 23.5 % for high, medium, and low volume centers, respectively. Multivariate analysis suggested that patients in low volume center were more likely to die compared to high volume center (Odds Ratio 2.06, 95 % CI 1.25 – 3.38, p = 0.004). Admission source was not associated with increased mortality.ConclusionsDirect admissions comprise the largest proportion of dissections regardless of volume strata, and they comprise the largest proportion in the low and intermediate volume cohorts. Admission to low volume center is an independent risk factor for increased mortality. Patients transferred to high volume centers from low volume centers have similar outcome as direct admits in terms of mortality.
Highlights
The purpose of this study is (1) to define the proportion of patients undergoing emergent open repair of thoracic aortic dissection admitted directly through the emergency room versus those transferred from outside hospitals and (2) to determine if a volume-outcomes relationship exists for those patients across admission types
Baseline demographics From January 1, 2004 to December 31, 2008 there were a total of 1,507 patients in the Nationwide Inpatient Sample (NIS) registry who underwent emergent open repair of an acute aortic dissection
A similar observation was made for high volume centers (7 out of 66 patients (10.6 %) and 5 out of 49 patients (10.2 %) for direct admission (DA) and transfer admission (TA)). These findings suggest that center volume may be a more important factor in determining outcome than admission type
Summary
The purpose of this study is (1) to define the proportion of patients undergoing emergent open repair of thoracic aortic dissection admitted directly through the emergency room versus those transferred from outside hospitals and (2) to determine if a volume-outcomes relationship exists for those patients across admission types. Numerous studies have demonstrated a volume-outcomes relationship for complex surgical procedures [5,6,7]. The observation was subsequently expanded to other cardiothoracic procedures [8,9,10], including emergent repair for acute aortic dissection [11]. One proposed explanation for better outcomes at high volume centers is survival bias, especially in the setting of emergent procedures. Because high volume centers accept a greater proportion of transfer patients, who are able to survive the added duration of a transfer, those centers may be treating patients who are already preselected to have improved outcomes
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