Data Extraction
Microsoft Office Excel 2016 (Microsoft Corp., Redmond, WA, USA) was used for data extraction. Two reviewers (D.A. and G.T.) independently extracted the data and recorded all data with a standardized form. All two-arm (two groups reported) studies with a within-study comparison of different hypothermia regimens, regardless of cerebral perfusion strategy, were extracted. The different levels of hypothermia were classified as following: deep hypothermia (≤20°C), moderate hypothermia (20.1°C to 25°C), mild hypothermia (≥ 25.1°C). The cutoff of 20°C to separate the patients into moderate vs. deep hypothermia cohorts was consistent with the International Aortic Arch Surgery Study Group (IAASSG) consensus guideline regarding the nomenclature of hypothermia during aortic arch surgery 10. In the literature, moderate hypothermia is often referred to as low-MHCA, while mild hypothermia is often considered high-MHCA. Concerning the location of temperature measurement, the rectal temperature was reported in almost all studies. If no rectal temperature was present in a publication, the nasopharyngeal temperature was reported. Outcomes were considered early outcomes when they occurred within 30 days postoperatively or during the period of initial hospital admission. Extracted baseline characteristics and outcome measures are provided in Supplementary Material, Table S1.