Cytokines such as such as TNF-a, IL-1, IL-6 correlate with the severity of pancreatitis.Neuroendocrine pathways, such as the sympathetic nervous system or parasympathetic nervous system, in turn, have some impact on the immune systems, through a-2 adrenoreceptor stimulation or the cholinergic anti-inflammatory pathway. The investigators aim to use Dexmedetomidine Hydrochloride to decrease the activity of sympathetic nervous system, thus relieve inflammation response.

Infected pancreatic necrosis (IPN) and multiple organ dysfunction syndrome (MODS) are major complications of acute pancreatitis which determine disease severity and outcome.It is concluded that systemic inflammation in SAP characterized by the endocrine release of different cytokines, such as TNF-a, IL-1, IL-6 and many others. These cytokines correlate with the severity of pancreatitis.

Neuroendocrine pathways, such as the sympathetic nervous system or parasympathetic nervous system, in turn, have some impact on the immune systems, through a-2 adrenoreceptor stimulation or the cholinergic anti-inflammatory pathway. Dexmedetomidine Hydrochloride is a high selected a-2 adrenoreceptor agonists.Some studies have shown that Dexmedetomidine Hydrochloride could improve the outcome of sepsis patients and decrease the development of organ failure.

The investigators aim to use Dexmedetomidine Hydrochloride to decrease the activity of sympathetic nervous system,thus relieve inflammation response.

Inclusion Criteria:

• Patients diagnosed with severe acute pancreatitis within 48h
• APACHE II≥8
• Patients or the family agreed to receive the treatment, and signed the informed consents

Exclusion Criteria:

• Patients were allergy to the drug
• Patients were diagnosed with Arrhythmia
• Patients with artificial permanent pacemaker implantation