IL6 and acute respiratory distress syndrome: Xuebijing injection improved oxygenation index (SMD 1.08 [95 % confidence interval (CI) 0.79–1.38]), reduced the incidence of acute respiratory distress syndrome (RR 0.56 [95 % CI 0.42–0.74) and all-cause mortality (RR 0.48 [95 % CI 0.34–0.67]), and decreased serum tumor necrosis factor-alpha (SMD -1.33 [95 % CI -1.50 to −1.17]) and interleukin-6 levels (SMD -1.35 [95 % CI -1.52 to −1.17]).