The effect of volume on esophageal cancer resections: what constitutes acceptable resection volumes for centers of excellence?

Abstract

Objective: Volume-outcome relationships for esophageal cancer resection have been well described with centers of excellence defined by volume. No consensus exists for what constitutes a "high-volume" center. We aim to determine if an objective evidence-based threshold of operative volume associated with improvement in operative outcome for esophageal resections can be defined.

Methods: Retrospective analysis was performed on patients undergoing esophageal resection for cancer in the 1998 to 2005 Nationwide Inpatient Sample. A series of multivariable analyses were performed, changing the resection volume cutoff to account for the range of annual hospital resections. The goodness of fit of each model was compared by pseudo r(2), the amount of data variance explained by each model.

Results: A total of 4080 patients underwent esophageal resection. The median annual hospital resection volume was 4 (range: 1-34). The mortality rate of "high-volume" centers ranged from 9.94% (>or=2 resection/year) to 1.56% (>or=30 resections/year). The best model was with an annual hospital resection volume greater than or equal to 15 (3.87% of data variance explained). The difference in goodness of fit between the best model and other models with different volume cutoffs was 0.64%, suggesting that volume explains less than 1% of variance in perioperative death.

Conclusion: Our data do not support the use of volume cutoffs for defining centers of excellence for esophageal cancer resections. Although volume has an incremental impact on mortality, volume alone is insufficient for defining centers of excellence. Volume seems to function as an imperfect surrogate for other variables, which may better define centers of excellence. Additional work is needed to identify these variables.

Figure 1. Graph of in-hospital mortality rates for individual hospitals by annual hospital esophageal resection volume

These data represent the annual hospital mortality rates of in-hospital death at 1,506 different hospitals. The data points have been staggered to illustrate the trend, due to the high frequency of overlapping values.

Figure 2. Graph showing the different mortality rates above and below each volume threshold

Squares indicate the mortality rates of hospitals with annual esophagectomy volumes for esophageal cancer less than the volume threshold. Triangles indicate the mortality rates of hospitals with annual esophagectomy volumes for esophageal cancer greater or equal to the volume threshold. The difference between each pair of mortality rates at a given annual hospital volume is statistically significant for all volume thresholds except ≥29 and ≥34. Associated data are listed in Table 2.

Figure 3. Graph of goodness-of-fit versus annual hospital resection volume

Each point represents one resection volume. McFadden’s pseudo r² is shown as percent. Dashed line represents “baseline” McFadden’s pseudo r² from the model without resection volume (3.23%).