Dexmedetomidine Pharmacokinetics-pharmacodynamics in Mechanically Ventilated Children With Single-organ Respiratory Failure

Inclusion Criteria: * patients (m/f) admitted to the paediatric intensive care unit * expected to require at least 24h of mechanical ventilation * patient age : 1 month-15 years * patients with single-organ respiratory failure Exclusion Criteria: * patients with neurologic conditions that prohibit an evaluation of adequate analgosedation * no arterial catheter in place at inclusion * patients who have received another investigational drug within 30 days * patients on continuous infusion with neuromuscular blockers * patients with a life expectancy \<72h * patients with a known allergy to lorazepam, midazolam and/or morphine * heart block * pre-existing bradycardia * hemodynamically unstable patients (Wernovsky index \> 16 points) after full fluid replacement with crystalloid * patients with significant renal insufficiency (creatinine plasma level 1 month-5 year : \> 1 mg/dl ; 5-10 years : \>1.2 mg/dl; \> 10 years : \> 1.5 mg/dl) * patients with significant hepatic insufficiency (aspartate aminase \>950 UI/L and prothrombin time \< 60 or INR \>1.4) * previous treatment with α2-adrenoreceptor agonist clonidine within 14 days