Study and patient characteristics and clinical outcome
Individual study characteristics are presented in Supplementary Material, Table S4. Ten studies were from United States, six from Japan, four from China, two from Canada, United Kingdom, France, Greece and Germany, one from Austria, Korea, Russia and Saudi Arabia. References of the studies included in this meta-analysis are available in the Online Data Supplement. A total of 12370 patients were included in the final analysis. Pooled patient and procedural characteristics are presented in Table 1. The mean age was 60.4 years in the DHCA group, 59.5 years in the MHCA group and 60.8 years in the mild HCA group. Acute aortic dissections were mainly operated under mild HCA (67.4%), whereas degenerative aneurysms under DHCA (41.5%). The mean lowest rectal temperature was 18.7 °C in the DHCA group, 24.0 °C in the MHCA group and 28.0 °C in the mild HCA group. Mild hypothermia was always used in conjunction with selective cerebral perfusion, most commonly unilateral antegrade cerebral perfusion (88.4%). Retrograde cerebral perfusion (RCP) was mainly utilized in the presence of deep hypothermia (40.2%) (Table 1). Hemiarch surgery was largely done under DHCA (83.1%), whereas total aortic arch surgery was done under moderate HCA (21.4%).
Patients operated under mild hypothermia levels experienced shorter cardiopulmonary bypass (CPB) and aortic cross clamp (ACC) times. Pooled clinical outcome measures for different hypothermia levels are presented in Table 2. Heterogeneity was high in all outcome measures.