Table 1.

Study characteristics of the included studies

Authors, year, and journal	Design	Country	Period	Frailty measure	Inclusion criteria	Exclusion criteria	Funding
McGuckin et al., Anaesthesia [26]	Retrospective Cohort	United Kingdom	June 2012 – January 2013	CFS	Age ≥ 65 Unscheduled non-cardiac surgery Stratified data: Colorectal and upper gastrointestinal surgery	None	Research institute
Tan et al., World Journal of Emergency Surgery [27]	Prospective Cohort	Singapore	June 2016–February 2018	MFI	Age ≥ 65 Emergency abdominal surgery (including diagnostic laparoscopies and emergency abdominal wall hernia repairs)	Vascular, gynaecological and transplant surgeries Emergency operations for complications of elective surgery Patients who were not expected to survive the index admission	University, Hospital
Parmar et al., Annals of Surgery[28]a	Prospective cohort	United Kingdom	20 March 2017–19 June 2017	CFS	Age ≥ 65 Expedited, urgent, or emergency surgical abdominal procedure for gastrointestinal pathology (laparoscopic or open procedure) Returning to theatre for any major postoperative complication/dehiscence	Diagnostic intervention Appendicectomy only Cholecystectomy only Vascular surgery, including abdominal aortic aneurysm repair Laparotomy/laparoscopy for pathology caused by blunt or penetrating trauma	Research foundation
Carter et al., British Journal of Surgery [29]a	Prospective cohort	United Kingdom	20 March 2017–19 June 2017	CFS	Age ≥ 65 Expedited, urgent, or emergency surgical abdominal procedure for gastrointestinal pathology (laparoscopic or open procedure) Returning to theatre for any major postoperative complication/dehiscence	Diagnostic intervention Appendicectomy only Cholecystectomy only Vascular surgery, including abdominal aortic aneurysm repair Laparotomy/laparoscopy for pathology caused by blunt or penetrating trauma	Research foundation
Arteaga et al., European Journal of Trauma and Emergency Surgery [30]	Prospective cohort	Spain	September 2017–April 2019	CFS	Age ≥ 70 Emergency abdominal surgery	Moderate-severe cognitive deterioration Terminal illness, defined as a life expectancy of less than 6 months	None
Vilches-Moraga et al., Aging Clinical and Experimental Research [31]	Prospective cohort	United Kingdom	September 2014–March 2017	CFS	Age ≥ 75 Emergency general surgery	Diagnostic intervention Appendicectomy only Cholecystectomy only Vascular surgery, including abdominal aortic aneurysm repair Laparotomy/laparoscopy for pathology caused by blunt or penetrating trauma	None

MFI Modified Frailty Index, CFS Clinical Frailty Scale

^aFor those studies, patients were part of the National Emergency Laparotomy Audit (NELA), which has specific inclusion and exclusion criteria. Only important criteria have been mentioned in the table. Moreover, the articles from Parmar and Carter report results from the same cohort