Anesthetics and brain protection

PURPOSE OF REVIEW: There is a considerable risk of cerebral ischemia during anesthesia and surgery. Anesthetic agents have been shown to have a profound effect on the pathophysiology of cerebral ischemia. The present review provides a brief historical review and details new information about the anesthetic effects on the ischemic brain. RECENT FINDINGS: Although anesthetics have been shown to reduce ischemic cerebral injury, the durability of this neuroprotection has been questioned. Recent data indicate that, under the right circumstances, anesthetic neuroprotection can be sustained for at least 2-4 weeks; the durability of this protection is dependent upon the experimental model, control of physiologic parameters and the assurance of the adequacy of reperfusion. In addition, volatile anesthetics have been shown to accelerate postischemic neurogenesis; this suggests that anesthetics may enhance the endogenous reparative processes in the injured brain. SUMMARY: The available data indicate that anesthetics can provide long-term durable protection against ischemic injury that is mild to moderate in severity. Experimental data do not provide support for the premise that anesthetics reduce injury when the ischemic injury is severe.     

Anesthetics and the brain

The action of anesthetics on the nervous system can be understood by considering their possible interactions with neuronal function. Anesthesia may be produced by a change in the balance of inhibitory synapses (notable via GABAa receptors) and excitatory synapses (notably glutamate receptors). Our knowledge of the specific mechanisms of anesthetic drugs and the structures in the CNS remains inadequate to explain the anesthetic state by one mechanism. The action of anesthetics can also be considered based on the action of the drugs on cerebral physiology, notably CMR, CBF, metabolic coupling, and autoregulation. Some specific anesthetic recommendations can be made for certain neurosurgical procedures and pathology based on the effects on physiology.     

Evaluation of cerebral metabolism]

The brain requires high amounts of energy for cellular homeostasis and neurological functions. This energy is mainly supplied by the oxidation of glucose, although other substrates may be used in critical situations. The capacity of the brain to conserve energy is illustrated by flow metabolism coupling, and by the separation between functional and basal activity. The evaluation of cerebral metabolism is defined as the assessment of energy substrates availability and utilization. This evaluation may be performed in physiological or pathological conditions, at a regional or at the global level, at rest or during activation processes. The main techniques discussed in this review include monitoring of venous blood in the jugular bulb, cerebral microdialysis, near infrared spectroscopy, cerebral oximetry using microprobe electrodes, positron emission tomography, magnetic resonance and the magnetoencephalography.