• Adequate sedation is of paramount importance to avoid stress and pain in mechanically ventilated patients. It is usually achieved by infusing sedatives (benzodiazepine) and analgesic (opiate) drugs.
• This combined sedation may not be sufficient in some instances.
• The aim of this study is to evaluate whether addition of a third substance, ketamine, allows the achievement of better sedation and avoids the use of neuromuscular blocking agents.

• Mechanical ventilation is widely used in critically ill patients. Sedation is used in most instances to alleviate symptoms of pain and distress. It usually consists of an association of opiates and benzodiazepines.
• In some instances, pain and agitation persist despite this combined sedation regimen. In such cases, the clinicians have the choice between increasing dosage of these 2 substances which may increase their adverse effects (mainly hypotension) and/or adding a neuromuscular blocking agent which is not devoid of adverse effects (mainly the onset of neuromyopathy of critical illness).
• This study will assess the safety, efficacy and cost-effectiveness of adding ketamine, a well known anesthetic agent, to a combination of midazolam and sufentanil when this combination is not sufficient to reach acceptable sedation target.

Inclusion Criteria:

• Mechanically ventilated patients who receive adequate dosing of sedative agents (midazolam > 0.15 mg/kg/h plus sufentanil > 0.3 mcg/kg/h)
• Persistence of agitation indicating that sedation is not appropriate, as assessed by validated sedation scales (Harris scare; Motor Activity Assessment scale).

Exclusion Criteria:

• Pregnancy
• Patient who already receives neuromuscular blocking agents