The Effects of Minimum Caseload Requirements on Management and Outcome in Abdominal Aortic Aneurysm Repair

Abstract

Background: The German quality assurance guideline on abdominal aortic aneurysm (AAA) was implemented by the Joint Federal Committee (Gemeinsamer Bundesausschuss, G-BA) in 2008. The aims of this study were to verify the association between hospital case volume and outcome and to assess the hypothetical effect of minimum caseload requirements.

Methods: The German diagnosis-related groups statistics for the years 2012 to 2016 were scrutinized for AAA (ICD-10 GM I71.3/4) with procedure codes for endo - vascular or open surgical treatment. The primary endpoint was in-hospital mortality. Logistic regression models were used for risk adjustment, and odds ratios (OR) were calculated as a function of the annual hospital-level case volume of AAA. In a hypo - thetical approach, the linear distances for various minimum caseloads (MC) were evaluated to assess accessibility.

Results: The mortality of intact AAA (iAAA) was 2.7% (men [M] 2.4%, women [W] 4.2%); ruptured AAA (rAAA), 36.9% (M 36.9%, F 37.5%). An inverse relationship between annual hospital case volume of AAA and mortality was confirmed (iAAA/rAAA: from 3.9%/51% [<10 cases/year] through 3.3%/37% [30-39 cases/year] to 1.9%/28% [≥ 75 cases/year]). For a reference category of 30 AAA procedures/year, the following significant OR were found: 10 AAA cases/year, OR 1.21 (95% confidence interval [1.20; 1.21]); 20 cases, OR 1.09 [1.09; 1.09]; 50 cases, OR 0.89 [0.89; 0.89]; 75 cases, OR 0.82 [0.82; 0.82]. In a hypothetical centralization scenario with assumed MC of 30/year, 86% of the population would have to travel less than 100 km to the nearest hospital; with an MC of 40, this would apply to only 50% (without redistribution effects).

Conclusion: In the observed period, a significant correlation was confirmed between high annual case volume and low in-hospital mortality. A minimum caseload requirement of 30 AAA operations/year seems reasonable in view of the accessibility of hospitals. Cite this.

Figure 1

Mortality after AAA treatment in hospital volume groups (patient-level analysis): a) iAAA; b) rAAA. Cumulated for years 2012 to 2016; confidence intervals of accumulated mortality calculated according to Wilson (17). AAA, Abdominal aortic aneurysm; i, intact; r, ruptured

Figure 2

Association between hospital volume and in-hospital mortality for patients with intact AAA. Estimated odds ratios with pointwise confidence intervals for volume modeled as a continuous variable (a) (reference: hospitals with a caseload of 30 /year) and volume modeled as a dichotomized variable (b). Adjusted for sex, age, comorbidity (Elixhauser score), type of admission, type of diagnosis, and treatment modality (open aortic repair vs. endovascular aortic repair); cumulated for years 2012 to 2016; For b):: the red line corresponds to the OR estimate for lower vs. higher caseload. For each minimum caseload requirement from 2 to 100 a separate regression model was calculated: The gray band shows the 95% confidence interval; the blue line, the smoothed estimate. AAA, Abdominal aortic aneurysm; OR, odds ratio

Figure 3

Geographical accessibility of hospitals according to hypothetical minimal annual caseload requirements (“what-if” scenario, without applying redistribution effects) Reference year = 2016 AAA, Abdominal aortic aneurysm; MC, minimal caseload of AAA operations per year

eFigure 1

Patient flow chart * Surgical treatment of the aneurysm by open or endovascular repair. Hybrid operations and other unspecific codes were excluded from this analysis. AAA, Abdominal aortic aneurysm; i, intact; r, ruptured; EVAR, endovascular aortic repair; OAR, open aortic repair

eFigure 2

Lorenz curve (proportion of treated patients vs. proportion of treating hospitals) for treatment of AAA in 2016 a) All AAA; b) iAAA and rAAA separately Point markers and data labels for steps between hospital volume groups. AAA, Abdominal aortic aneurysm; CL, caseload; i, intact; r, ruptured

eFigure 3

Absolute number (a) and relative distribution (b) of hospitals in volume groups per year (2012–2016)

eFigure 4

Mortality after AAA treatment in hospital volume groups (hospital-level analysis) Cumulated for years 2012 to 2016; AAA, abdominal aortic aneurysm; Q, quartile