Inclusion Criteria:  Adult septic shock patients (age≥18 years old) Norepinephrine dose was more than or equal to 15μg/min  Exclusion Criteria:  Age older than 85 years Serum creatinine more than 177 μmol/L Acute myocardial ischemia Acute mesenteric artery ischemia Pregnancy Expected death within 24 hours.