BACKGROUND : The objective of the current study was to assess the impact of case mix index at the hospital level on postoperative outcomes among Medicare beneficiaries who underwent hepatopancreatic surgery.

METHODS : Medicare beneficiaries who underwent hepatopancreatic surgery between 2013 and 2017 were identified and analyzed. The primary independent variable, Case Mix Index, is a freely available metric; the primary outcome was textbook outcome defined as the absence of complications, extended length of stay, readmission, and mortality.

RESULTS : Among 37,412 Medicare beneficiaries, 64.9% (n = 24,299) underwent a pancreatectomy and 35.1% (n = 13,113) underwent hepatectomy. The overall incidence of textbook outcome was 47.2%, which varied by case mix index (low case mix index: 41.6% vs high case mix index: 51.3%), as did extended length of stay (low case mix index: 27.9% versus high case mix index: 19.3%), complications (low case mix index: 33.3% vs high case mix index: 24.7%), and 90-day mortality (low case mix index: 12.5% vs high case mix index: 6.3%). After controlling for hepatopancreatic-specific surgical volume and hospital teaching status, multivariable analyses revealed that patients who underwent surgery at a low case mix index hospital had 28% decreased odds (95% confidence interval 0.66-0.79) of achieving a textbook outcome versus patients from a high case mix index hospital. Moreover, patients at a low case mix index hospital had 39% increased odds of extended length of stay (95% confidence interval 1.23-1.59), 48% increased odds of experiencing a complication (95% confidence interval 1.32-1.65), and 56% increased odds of 90-day mortality (95% confidence interval 1.31-1.87).

CONCLUSION : Case mix index was strongly associated with the probability of achieving a textbook outcome after hepatopancreatic surgery. Hospitals with a higher case mix index were more likely to perform hepatopancreatic surgeries with no adverse postoperative outcomes.