Determination of the 90% Effective Dose of a Sufentanil Bolus in Analgesia During Lateral Decubitus of Mechanically Ventilated Patients

Inclusion Criteria: * 48th hour of mechanical ventilation * mechanical invasive ventilation * 48th hour midazolam sedation * Behavioral Pain Scale (BPS) at 3 or 4 * mechanical ventilation of 5 days duration Exclusion Criteria: * Pregnant or breast-feeding woman * Impossibility of evaluation of the BPS tetraplegia, curare-link , post anoxic coma encephalic death * Indication of deep conscious-sedation, malignant cranial trauma, toxic shock, acute respiratory distress syndrome * Extra renal clearance OU people in hemodialysis * Severe renal failure (creatinine clearance \<15ml/min) * Severe hepatic failure * State of consciousness with impossibility to use self-assessment scale * Body mass index \>35 ou \<18 * Sufentanil midazolam paracetamol allergy or contraindication * Guardianship or confirmed criminal Subject who give his informed consent * Morphinic other than sufentanil (morphine, alfentanil fentanyl, remifentanil, nalbuphine, codeine, buprenorphine) * Antalgic other than sufentanil and paracetamol ( tramadol nefopam, ketamine, dextropropoxyphene, non steroidal anti-inflammatory drug ) * MAO inhibitors