Near infrared spectroscopy evaluated cerebral oxygenation during anesthesia

Likely, maintained organ and notably cerebral perfusion, secures rapid recovery following anesthesia. To secure cerebral blood flow (CBF) at least mean arterial pressure (MAP) and the arterial carbon dioxide tension (PaCO₂) need to be considered. CBF is "autoregulated", i.e. stays more or less stable within a MAP of 50-150 mmHg, but the lower limit appears to depend on the central blood volume and/or cardiac output, illustrated by a decrease in CBF at a MAP of 80 mmHg with a compromised central blood volume, while CBF remains constant with a MAP < 40 mmHg, if the central blood volume is maintained. During anesthesia, MAP is often around 50 mmHg meaning that it remains unknown whether CBF is maintained, why an evaluation of CBF, e.g. by near-infrared spectroscopy (NIRS) seems desirable. NIRS is sensitive to changes in PaCOa₂, detects hypoxemia, identifies cerebral autoregulation as well as regional distribution of CBF. As summarized, especially elderly patients and patients undergoing complex surgery and notably heart and liver surgery, seem to benefit from a strategy focusing on maintaining NIRS-determined cerebral oxygenation during anesthesia. Similarly, NIRS may be applied to guide the ventilatory strategy during anesthesia when there are large deviations in metabolism, seen when clamping of the aorta and with reperfusion of the lower body during open aortic surgery, as with hepatectomy and following reperfusion of the donated liver during liver transplantation surgery. Finally, it is illustrated how NIRS can be applied to select sympathomimetic agents, used to correct anesthesia-induced hypotension in order to preserve CBF and skin oxygenation.