Neuro anesthetic considerations

Abstract

Traumatic brain injury is a contributing factor in 30.5 % of all injury related deaths in the United States. Primary traumatic neurological injury is the damage caused by the initial trauma from mechanical impact to the skull and brain tissue due to acceleration, deceleration, rotation, or penetration. Secondary injury progresses after initial injury, resulting in additional brain damage and worsened neurological outcome. The duration of intraoperative hypotension along with hypocapnea, hypercapnea, hyperglycemia, and hypoglycemia can all worsen secondary brain injury. A resuscitation continuum begins at the point of injury, continues on to the operating room then to the intensive care unit. Specialized care in designated trauma centers has been demonstrated to improve outcome in patients with serious injury. Patients with traumatic brain injury will most often need endotracheal intubulation, facilitated by the use of anesthesia induction agents and muscle relaxants. Selection of the best induction agent is based on level of consciousness, need for a muscle relaxant and hemodynamic stability. Induction drugs discussed include Midazolam, Scopolamine, Flumazenil, Propofol, Etomindate, Sodium Thiopental, Ketamine, Mannitol. Hypotension, hypoxia and hyperventilation should be avoided. Hypotension occurring during the first 6 h after head injury has the highest prediction of poor neurological outcome at discharge. Volatile agents (isoflurane, sevoflurane, desflurane) decrease cerebral metabolic rate while increasing cerebral blood flow. They uncouple autoregulation. However, at less than one MAC these affects are minimal and all three agents can be used at low doses in patients with traumatic brain injury. IV anesthetic agents including propofol, etomidate, and thiopental decrease cerebral blood flow, cause cerebral vasoconstriction, and decrease cerebral metabolic rate. Erythrocyte transfusions increased the cerebral tissue oxygenation in anemic patients with severe TBI with a low baseline brain tissue oxygen (PtiO2) levels (<15 mm Hg).