Dexmedetomidine pharmacokinetics during continuous venovenous hemofiltration and hemodiafiltration in critically ill patients

To determine the pharmacokinetics of dexmedetomidine during continuous venovenous hemofiltration and hemodialfiltration in critically ill patients. The measured values will be Cltot, ClCVVH(DF), Vd, T�, the amount of dexmedetomidine in ultrafiltrate and urine.