Non Invasive Monitoring Of Cerebral Oxygenation during General Anesthesia Using Cerebral Oximetry

Abstract

The human brain is highly perfused organ. Its blood supply come through Circle of Willis which is raised from basilar artery (come from two vertebral arteries) and anterior, middle cerebral arteries (comes from internal carotid arteries). The techniques to assess cerebral oxygenation available today can be classified into invasive or non-invasive. The invasive technology uses the parenchyma probes, which measure oxygen and biochemical parameters, depending upon the type of probe used. The non-invasive technique uses near infrared spectroscopy for transcranial cerebral oximetry. Near–infrared spectroscopy (NIRS) is non-invasive new technique for monitoring intracerebral oxygen saturation. It is a reliable indicator of peripheral cortical perfusion and provides continuous and non-invasive monitoring of intracerebral oxygen saturation. Cerebral oximetry has been studied for more than 30 years, and has been commercially available to clinicians for more than 2 decades. However, whereas pulse oximetry has been a standard of care for decades, only recently has cerebral oximetry been extensively studied and adapted to investigate changes in oxygen delivery to the brain and how the monitor may be used as a “first alert” of impending organ dysfunction. Cerebral Oximetry was designed to give health care providers information to guard against neurological injuries due to compromised cerebral tissue oxygenation. Cerebral tissue oxygen saturation values are important to clinicians because cerebral hypoxia (lack of oxygen supply to brain tissue) is one of the leading causes of brain injuries that occur in many surgical and clinical situations. Cerebral oximetry estimates the oxygenation of regional tissue by transcutaneous measurement of the cerebral cortex, an area of the brain that is particularly susceptible to changes in the demand and supply of oxygen, and which has a limited oxygen reserve. Measurement is based on the ability of light to penetrate the skull and determine hemoglobin oxygenation according to the amount of light absorbed by hemoglobin—a process called near-infrared spectroscopy (NIRS). Unlike pulse oximetry (which uses a single sensor), cerebral oximetry with NIRS uses 2 photodetectors with each light source. The technology allows selective sampling of tissue beyond a specified depth beneath the skin. Near-field photodetection then can be subtracted from far-field detection to provide selective measurements of tissue oxygenation. Adhesive pads applied over the frontal lobes both emit and capture reflected near-infrared light passing through the cranial bone to and from the underlying cerebral tissue. Despite impressive improvements in the overall safety of anesthetized patients in the past two decades, brain injury remains a major and growing problem. This is demonstrated by the on-going American Society of Anesthesiologists closed claims analysis. Brain injury (including brain damage, stroke & awareness) represents the single largest fraction (17%) of malpractice claims.