Evaluation of the Safety of Inhaled Sedation With Isoflurane in Head Trauma Patients

Intensive care management of patient with severe traumatic brain injury (TBI) includes deep and prolonged sedation with intravenous hypnotics (propofol, midazolam, ketamine) in combination with opioids to prevent and/or treat episodes of intracranial hypertension. However, some patients may develop tachyphylaxis with a gradual increase of administered intravenous hypnotics and opioids to maintain the same level of sedation. This situation leads to a failure in controlling intracranial pressure (ICP) and/or to the risk of adverse effects due to high-dose sedatives: haemodynamic instability, prolonged mechanical ventilation, neuromyopathy, delirium, withdrawal syndrome. Halogenated agents (Isoflurane, Sevoflurane) are a class of hypnotics routinely used in the operating room. However, doses used in surgical patients (\> 1 Minimal Alveolar Concentration, MAC) are not suitable in neuro-intensive care unit (ICU) patients at risk of intracranial hypertension because of the cerebral vasodilator effects of halogenated agents at this dosage, hence the risk of high ICP and compromised cerebral perfusion pressure. The use of halogenated agents has been recently possible in the ICU through dedicated medical devices (Sedaconda ACD, Mirus). Recommended dosage are lower in the ICU, i.e. 0.3-0.7 MAC, because of their association with intravenous hypnotics and the absence of surgical stimuli. Several clinical studies in general ICUs showed improved sedation quality, reduced duration of mechanical ventilation, faster arousal and shorter extubation time, and lower costs in halogenated group compared with control group receiving midazolam or propofol. At low doses, the effects on ICP and intracerebral haemodynamics of halogenated agents are minor according to the available literature. In addition, beneficial effects were found on cerebral ischaemic volume in animal models treated with halogenated agents. However, there is a need to explore the benefit-risk ratio of the use of halogenated agents in the severe TBI population. The investigator hypothesise that 0.7 MAC Isoflurane can be administered in this population without deleterious effect on ICP.