Les agents utilisés pour la sédation en neuro-réanimation

Escalate and De-Escalate Therapies for Intracranial Pressure Control in Traumatic Brain Injury

Severe traumatic brain injury (TBI) is frequently associated with an elevation of intracranial pressure (ICP), followed by cerebral perfusion pressure (CPP) reduction. Invasive monitoring of ICP is recommended to guide a step-by-step “staircase approach” which aims to normalize ICP values and reduce the risks of secondary damage. However, if such monitoring is not available clinical examination and radiological criteria should be used. A major concern is how to taper the therapies employed for ICP control. The aim of this manuscript is to review the criteria for escalating and withdrawing therapies in TBI patients. Each step of the staircase approach carries a risk of adverse effects related to the duration of treatment. Tapering of barbiturates should start once ICP control has been achieved for at least 24 h, although a period of 2–12 days is often required. Administration of hyperosmolar fluids should be avoided if ICP is normal. Sedation should be reduced after at least 24 h of controlled ICP to allow neurological examination. Removal of invasive ICP monitoring is suggested after 72 h of normal ICP. For patients who have undergone surgical decompression, cranioplasty represents the final step, and an earlier cranioplasty (15–90 days after decompression) seems to reduce the rate of infection, seizures, and hydrocephalus.

Pediatric head injury: a pain for the emergency physician?

The prompt diagnosis and initial management of pediatric traumatic brain injury poses many challenges to the emergency department (ED) physician. In this review, we aim to appraise the literature on specific management issues faced in the ED, specifically: indications for neuroimaging, choice of sedatives, applicability of hyperventilation, utility of hyperosmolar agents, prophylactic anti-epileptics, and effect of hypothermia in traumatic brain injury. A comprehensive literature search of PubMed and Embase was performed in each specific area of focus corresponding to the relevant questions. The majority of the head injured patients presenting to the ED are mild and can be observed. Clinical prediction rules assist the ED physician in deciding if neuroimaging is warranted. In cases of major head injury, prompt airway control and careful use of sedation are necessary to minimize the chance of hypoxia, while avoiding hyperventilation. Hyperosmolar agents should be started in these cases and normothermia maintained. The majority of the evidence is derived from adult studies, and most treatment modalities are still controversial. Recent multicenter trials have highlighted the need to establish common platforms for further collaboration.

[Sedation in neurointensive care unit]

The objectives for using sedation in neurointensive care unit (neuroICU) are somewhat different from those used for patients without severe brain injuries. One goal is to clinically reassess the neurological function following the initial brain insult in order to define subsequent strategies for diagnosis and treatment. Another goal is to prevent severely injured brain from additional aggravation of cerebral blood perfusion and intracranial pressure. Depending on these situations is the choice of sedatives and analgesics: short-term agents, e.g., remifentanil, if a timely neurological reassessment is required, long-term agents, e.g., midazolam and sufentanil, as part of the treatment for elevated intracranial pressure. In that situation, a multimodal monitoring is needed to overcome the lack of clinical monitoring, including repeated measurements of intracranial pressure, blood flow velocities (transcranial Doppler), cerebral oxygenation (brain tissue oxygen tension), and brain imaging. The ultimate stop of neurosedation can distinguish between no consciousness and an alteration of arousing in brain-injured patients. During this period, an elevation of intracranial pressure is usual, and should not always result in reintroducing the neurosedation.

[Inflammation and acute brain injuries in intensive care]

Patients with acute brain injuries or susceptibility to post-surgery stroke are a major therapeutic challenge for intensive care and anaesthesiology medicine. The control of systemic stress involved in brain damage is necessary to reduce the frequency and severity of secondary brain lesions. Inflammation is known to be directly involved in acute brain lesions. The brain is a major participant in inflammation control through activation or inhibition effects. The exact mechanisms involved in deleterious effects following acute brain injuries due to inflammation are still unknown. This non-exhaustive study will expose the principal processes involved in inflammatory brain disease and explain the consequences of peripheral inflammation for the brain. Neuroprotection strategies in acute neuroinflammation will be reported with a focus on anaesthetic agents and the inflammation cascade.

Hiérarchisation des traitements de l'hypertension intracrânienne chez le traumatisé crânien grave

The objective of the treatment of intracranial hypertension is to decrease intracranial pressure (ICP) while maintaining cerebral blood flow (CBF). Despite numerous treatments, none of them associates total efficiency and security. Systemic secondary cerebral injuries, which are responsible for cerebral ischemia, lead us to administer non specific treatments in order to optimize CBF and cerebral oxygenation. Thus, the goals are: 1) to maintain cerebral perfusion pressure> or =70 mmHg; 2) to control metabolic status by preventing hyperglycaemia, anaemia and hyperthermia; 3) to maintain normoxia and normocapnia (hypercapnia increases ICP and hypocapnia decreases CBF). Beside the neurosurgical evacuation of extra- and intraparenchymatous haematomas, osmotherapy and cerebrospinal fluid (CSF) evacuation are the two specific treatments of intracranial hypertension. Osmotherapy consists in an administration of a hypertonic solution which induces a decrease in cerebral water and finally in ICP. Mannitol (20%), which is the reference, associates osmotic and rheologic effects, and decreases CSF production too. Recent data conduct us to administer larger doses, between 0.7 and 1 g/kg in 15 minutes. Hypertonic saline solution associates osmotic effects and plasma volume loading. Thus, this solution is particularly appropriate in severe head injury with arterial hypotension. CBF evacuation decreases rapidly ICP without any major side-effect. Until now, there is no proof of a superior efficiency of a treatment for intracranial hypertension compared to another. Considering their mechanism of action, all of them are efficient but potentially dangerous too. Indeed, the choice between treatments depends on data which are issued from the multimodal monitoring. General non specific treatments are always necessary. Specific treatments are indicated if ICP is above 20-25 mmHg. Maintaining cerebral perfusion pressure represents the first therapeutic goal. If intracranial hypertension persists, evacuation of CBF or osmotherapy may be advocated. In case of refractory intracranial hypertension, it may be useful to deepen neurosedation. Controlled hypocapnia and barbiturates remain a third line therapy providing to monitor and maintain an appropriate CBF and cerebral oxygenation. Controlled hypothermia and decompressive craniectomy must be individually discussed.

Quelle sédation pour la prévention et le traitement de l'agression cérébrale secondaire ?

The aim of sedation and analgesia is to prevent secondary brain insult. The goals of sedation are the prevention and treatment of intracranial hypertension and systemic disorders. In such situation, the use of sedative and analgesic therapy should respect the rate of cerebral blood flow/cerebral oxygen consumption coupling while preserving cerebral perfusion pressure and decreasing the intracranial pressure. This treatment should have an analgesic and myorelaxing action with short and predictable time of action. The optimal agent with all these characteristics does not exist, but the combination of several pharmacological compounds may reach this goal. Benzodiazepines are the most frequently agents used. In most of cases they are associated with analgesics like opioids or ketamine. Opioids are the basis of analgesia because they do not produce brain haemodynamic alterations if arterial pressure is maintained. Ketamine, which use in this indication is matter of debate, has the advantage to maintain haemodynamics. Ketamine has no side effects on brain haemodynamics when used in combination with propofol or midazolam. Because of their side effects on haemodynamics and immune response, barbituric are no longer used as long term sedative agents. However, they are still recommended in cases of refractory intracranial hypertension. Propofol remains the optimal sedative agent because of its short duration action although its use is restricted because it is an expensive drug. Its use is recommended for short time sedation with or without opioids. The use of neuromuscular blockers should be focused on the patients with an intracranial hypertension refractory to standard treatment. The presence of brain damage in patients makes difficult to assess the level of sedation. One should avoid over sedation, which increases morbidity by prolongation of the duration of mechanical ventilation.

Evidence of acute tolerance to remifentanil in intensive care but not in anesthesia

We report the case of a 19-year-old man with a drug abuse history, admitted to the intensive care unit for head and chest trauma, who experienced an acute tolerance to sedative and respiratory depression effects of remifentanil, which was given as the sole agent for sedation. He did not exhibit any signs of drug tolerance or intraoperative awareness during prolonged remifentanil-based anesthesia using propofol or sevoflurane as adjuvants. Several recent studies support the hypothesis of a possible involvement of N-methyl-d-aspartate glutamate receptors. The clinical relevance of this report is that if a patient with a previously acute tolerance to remifentanil during sedation undergoes long-term surgery, and propofol or sevoflurane is coadministered in a remifentanil-based anesthesia, the patient will not necessarily develop opioid tolerance. It is of interest for anesthesiologists, given the high frequency of patients with drug abuse history who are admitted to intensive care units, often sedated with remifentanil, who undergo anesthesia for emergency surgery.

Effect of Ketamine on Dendritic Arbor Development and Survival of Immature GABAergic Neurons In Vitro

Ketamine, a noncompetitive antagonist of the N-methyl-D-aspartate type of glutamate receptors, was reported to induce neuronal cell death when administered to produce anesthesia in young rodents and monkeys. Subanesthetic doses of ketamine, as adjuvant to postoperative sedation and pain control, are also frequently administered to young children. However, the effects of these low concentrations of ketamine on neuronal development remain unknown. The present study was designed to evaluate the effects of increasing concentrations (0.01-40 microg/ml) and durations (1-96 h) of ketamine exposure on the differentiation and survival of immature gamma-aminobutyric acidergic (GABAergic) interneurons in culture. In line with previous studies (Scallet et al., 2004), we found that a 1-h-long exposure to ketamine at concentrations > or = 10 microg/ml was sufficient to trigger cell death. At lower concentrations of ketamine, cell loss was only observed when this drug was chronically (> 48 h) present in the culture medium. Most importantly, we found that a single episode of 4-h-long treatment with 5 microg/ml ketamine induced long-term alterations in dendritic growth, including a significant (p < 0.05) reduction in total dendritic length and in the number of branching points compared to control groups. Finally, long-term exposure (> 24 h) of neurons to ketamine at concentrations as low as 0.01 microg/ml also severely impaired dendritic arbor development. These results suggest that, in addition to its dose-dependent ability to induce cell death, even very low concentrations of ketamine could interfere with dendritic arbor development of immature GABAergic neurons and thus could potentially interfere with the development neural networks.