Effect Modification of Sex and Age for the Hospital Volume‐Outcome Relationship in Abdominal Aortic Aneurysm Treatment: Secondary Data Analysis of the Nationwide German Diagnosis Related Groups Statistics From 2005 to 2014

Figures

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  Figure 1. Case flowchart. EVAR indicates endovascular aortic repair; OAR, open aortic repair.

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  Figure 2. Association between in‐hospital mortality (primary outcome) and sex, age, comorbidity, and type of treatment: Forest plot of the underlying model. Sex was evaluated at median volume (14 cases) and median male age (72 years); age was evaluated at median volume (14 cases). To account for clustering of patients within hospitals, and to account for effect of calendar year, the year of treatment and hospital site code were entered as random effects.

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  Figure 3. Odds ratios and 95% CIs of the volume‐outcome relationship by sex (women [left] and men [right]) and age (indicated by color). The median annual volume (14 cases; indicated by vertical line) was set as reference. Odds ratios were compared with the median annual hospital volume (14 cases) and corresponding 95% CI evaluated at the median age within each age group.

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  Figure 4. Odds ratio of volume compared with an increased volume (5 additional cases a year) with 95% CIs by sex (women [left] and men [right]) and age (indicated by color) for all cases (open aortic repair and endovascular aortic repair [EVAR]). Each line behaves like the first derivative of the corresponding line of Figure 3. At each volume point, the regression coefficients were treated as normally distributed random variables. Then, all variables except the volume were set constant and the linear predictor of the 2 time points was calculated and subtracted. Then, the corresponding estimator of the SE was calculated. Finally, the linear predictor difference with 95% CI was retransformed to the odds ratio scale.

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  Figure 5. Predicted in‐hospital mortality depending on annual hospital volume by sex (women [left] and men [right]) and age (indicated by color) for endovascular aortic repair (A) and open aortic repair (OAR) (B), amended by highlighted extrema (black dots).

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  Figure 6. Predicted in‐hospital mortality depending on annual hospital volume by sex (women [left] and men [right]) and age (indicated by color) for all cases (open aortic repair and endovascular aortic repair [EVAR]), amended by highlighted extrema (black dots). Averaged on Figure 5A and 5B by EVAR proportion within each stratum. AAA indicates abdominal aortic aneurysm.