Delirium, cerebrovascular accidents, postoperative cognitive dysfunction (POCD), and spinal cord ischaemia are among the most devastating perioperative neurological outcomes. In an attempt to address these outcomes, it would be helpful to identify patients at risk, predict their short- and long-term outcomes, monitor them perioperatively, and possibly apply neuroprotective interventions aimed at improving such outcomes. There is no available methodology to test for and measure central nervous system (CNS) reserve in a way that a cardiac stress test would tell about cardiac reserve. Intraoperative monitoring of responsiveness of the awake patient is still considered the gold standard for early detection of neurological insult. However, when general anaesthesia is used, that modality monitoring is not available, and the evidence for the utility of EEG is at best controversial.Somato-sensory and motor-evoked potential have been used to detect spinal cord injury during spine surgery. However, it has its own limitations. There is considerable interest in neurological biomarkers with the hope that they would meet the current needs.
The ideal neurological biomarker should have similar characteristics to other markers of injury such as cardiac troponins. Thus, the â€˜brain troponinâ€™ should be CNS-specific, easily and cheaply measured in the blood, resistant to cytoplasmic and extracellular proteolytic activity, and not dependent on renal excretion. It should also have a high sensitivity and specificity for predicting short- and long-term outcomes. Consequently, its level should vary with the degree of CNS damage and improve with neuroprotective interventions.
In addition, a reliable neurological biomarker in the context of systemic inflammation, such as in severe sepsis or during cardiopulmonary bypass (CPB), would be important for monitoring the CNS as sepsis-induced encephalopathy prolongs intensive care unit stay and increases mortality.Although there is no strong support for the use of neurologicalbiomarkers in the prognosis of outcome after cardiac arrest, some authorities have recommended their use in the context of mild therapeutic hypothermia.
Biomarkers can be classified as biomarkers of susceptibility, effect, and exposure. Susceptibility biomarkers reveal subjects with genetically mediated predisposition to a specific condition. Effect biomarkers measure early biological effect such as structural or functional changes in affected cells or tissues, or clinical disease. Exposure biomarkers are used to measure chemicals or their metabolites to determine a subject's exposure to them.Thus, the identification ofneurological biomarkers that fulfil these characteristics would be useful for the identification of patients at risk and the detection and treatment of those with on-going neurological insults.
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