Near Infrared Spectroscopy (NIRS) or Cerebral Oximetry
Near infrared spectroscopy (NIRS) measures the oxygenation of the haemoglobin in the cerebral tissue lying just underneath a probe. The probe is most often placed on the forehead since hair follicles affect the readings. Some doubts have been raised whether NIRS specifically measures the cerebral tissue or is contaminated by signals from extracerebral tissue it passes through. Furthermore, as haemoglobin absorbs infrared light, NIRS is affected by underlying blood of extravascular origin, such as in subdural haematomas, contusions, subarachnoid blood, as well as changes in cerebral blood volume (CBV). These factors are difficult to decipher, and at present the use of NIRS in TBI patients is controversial. However, by using more than one sensor and by focusing on trends, NIRS readings might be of value in this patient group.