Dexmedetomidine hydrochloride ,a relatively new drug in Chinais ,is a highly selective, potent a2-adrenoceptor agonist with significant analgesic, sedative and anxiolytic effects. The morbid obesity in Chinese population is rapidly increasing. But the pharmacokinetics of the drug in these people is still unknown.This research was designed to study the pharmacokinetics of dexmedetomidine in Chinese morbidly obese population.

For the obese are sensitive to the disease such as hypertension, ischaemic heart disease and diabetes, the changes of the state may affect the pharmacokinetics of dexmedetomidine. Besides,the clearance of dexmedetomidine is parallel with liver function and it is excreted by kidney, so differences in the obese may be expected.

About 10 obese patients and 10 matched healthy volunteers with normal weight would be chosen to receive a normal dosage of dexmedetomidine. And venous samples will be collected in different time points. Next the investigators can get the plasma concentration of dexmedetomidine by the use of HPLC-MS. And then the plasma concentration could be analyzed.

Inclusion Criteria:

1. Weight:28≦BMI≦45 and 18.5≦BMI≦24
2. Written informed consent from the patient or the relatives of the participating patient.

Exclusion Criteria:

1. A previous history of intolerance to the study drug or related compounds and additives.
2. Existing significant haematological, endocrine, metabolic or gastrointestinal disease.