Near Infrared Spectroscopy

Various bedside methods for cerebral monitoring are introduced in neurointensive care unit (NICU) for neurological or neurosurgical critically ill patients. Early diagnosis and treatment of abnormalities in cerebral perfusion, cerebral metabolism, or cerebral oxygenation are the main objective of the treating clinician in NICU to prevent further brain injury, termed as “secondary brain insult.” These cerebral monitors can be further divided into either invasive or noninvasive monitors (Table 11.1). Near-infrared spectroscopy (NIRS)-based cerebral oximetry is an important part of multimodel monitoring in neurocritically ill patients to measure cerebral oxygenation. NIRS uses the near-infrared spectrum of light to penetrate skin, subcutaneous tissue, bone, and finally brain tissue, to estimate oxy-/deoxyhemoglobin concentration changes and oxidation status of cytochrome c oxidase, and, finally, to measure the cortical regional oxygen saturation (rSO2) [1]. The bifrontal light-emitting diodes placed on the forehead at 4 cm apart provide information about oxygen saturation within the frontal lobe (Fig. 11.1) [2]. These probes contain a fiber optic light source and light detectors. Light sources release light in the infrared range through a process of either stimulated emission of radiation or through light-emitting diodes (Fig. 11.2) [2]. The threshold for cerebral ischemia is set at <50% or 20% drop from the baseline value [3]. Rather than the absolute value, it would be useful to have a continuous data on trends of relative change from baseline. Brain tissue hypoxia has been associated with worse outcome. That makes the cerebral oxygenation monitoring an important pillar of cerebral care in neurocritically ill patients in NICU. Various cerebral oxygenation monitors are available in the market (Table 11.1) NIRS-based cerebral oximetry is a noninvasive cerebral oxygenation monitor and is easy to use or interpret.