Neuromonitoring during adult cardiac surgery

The brain has been considered an index organ for global tissue perfusion because of the physiological processes aimed at flow preservation to vital organs of the body[1].When cerebral perfusion is compromised, other organs are likely inadequately perfused as well. It would therefore be prudent to monitor cerebral perfusion based on the proposition that interventions aimed at its preservation will likely result in adequate tissue perfusion of the whole body and reduced complications related to ischemia of various organs. It is worth emphasizing the difference between tissue perfusion and tissue oxygen supply. It is a consensus that the normal oxygen supply/demand ratio is important to normal tissue metabolic physiology at the molecular level. Because oxygen demand is largely related to perfusion, it is perfusion that remains the main focus of all clinicians in the cardiac operating room[1]. Very brief periods of cerebral hypoperfusion occur frequently during cardiac surgery due to a multitude of factors (reduced cardiac output, low pump flow, decreased perfusion pressure, etc.) but are of minute clinical significance. It is prolonged or cumulative hypoperfusion, particularly in watershed areas of the brain, undetected by standard monitors such as arterial blood pressure or pulse oximetry, that leads to brain tissue injury and adverse outcomes[2]. To date, no device has been developed that can reliably, continuously and non-invasively monitor global cerebral tissue perfusion directly. A number of existing monitors can indirectly assess regional cerebral perfusion and provide information useful in managing cerebral blood flow and oxygen supply. Cerebral oximetry