“…There is significant variation in the included observational trials regarding sample size (range of 83 to 10,021 patients), hypothesis (ERAS vs historical control; impact of compliance with ERAS and outcomes), and design (prospective with matched historical controls, entirely retrospective). Of the included 26 observational trials, 21 reported the effect of ERAS on overall complications, with seven studies demonstrating that implementation of an ERAS protocol led to reduced overall post-operative morbidity [3,6,[9][10][11][12]14,15,[18][19][20][21]23,[25][26][27]28,29,[30][31][32]. Five of these studies were comparing the ERAS protocol to historical controls [3,9,10,11,31].…”