Cerebral Physiology During Cardiac Arrest

The EEG is often used to assess cerebral ischaemia during procedures such as cardiac and neurosurgery. Concurrent EEG monitoring during a cardiac arrest has shown an initial slowing of the EEG waves which then progress to an isoelectric line within approximately 10 - 20 seconds and remain flat during the cardiac arrest until the resumption of cardiac output in early defibrillated arrhythmia'. In cases of prolonged cardiac arrest, however EEG activity may not return for many tens of minutes after cardiac output has been returned. Therefore, during cardiac arrest impaired cerebral blood flow leads to a lack of electro physiological activity in the cortex, which is made worse, as the time from the initial period of ischaemia to adequate resuscitation is increased. Studies in animals have demonstrated that an absence of cortical activity as measured by EEG correlates with an absence or reduction in activity of the deep brain structures as measured by in-dwelling electrodes.