Septic shock is one of the major causes of death worldwide with in-hospital mortality rates varying between (11.9% to 47.2 %). Alterations in microcirculatory blood flow were associated with high risk of organ dysfunction and death. Experimental studies on septic rats revealed that dexmedetomidine treatment can effectively reduce the generation of inflammatory mediators and yields beneficial effects on endotoxemic animals' microcirculation.

Prospective randomized double blinded study. Investigators planned to enroll (40 cases diagnosed with severe sepsis and/or septic shock ) admitted in 50-bed trauma and surgical ICU Cairo University hospital. Demographic data, cause of ICU admission, source of sepsis, APACHE II score, SOFA score 24 hours after admission. Microcirculatory variables (MFI), peripheral perfusion (PI) and metabolic variables will be measured before drugs administrations and at 2, 4, 6, 24 hours thereafter. The total dose of the infused drugs, The requirement of vasopressor will be evaluated as yes/no and total dose of vasopressor will be calculated.

Inclusion Criteria:

• Age more than 18 years old
• All mechanically ventilated patients who will be clinically suspected of having severe sepsis/septic shock defined by the criteria of the American College of Chest Physicians/ Society of Critical Care Medicine Consensus Conference

Exclusion Criteria:

• Age < 18 years old
• Pregnant patient
• Acute hepatitis or severe liver disease (Child-Pugh class C)
• Left ventricular ejection fraction less than 30%
• Heart rate less than 50 beats/min
• Second or third degree heart block
• Systolic pressure < 90 mmHg despite of infusion of 2 vasopressors