Cerebral Physiology During Cardiac Arrest
Immediately following a cardiac arrest, blood pressure drops to immeasurable levels. Properly performed chest compressions, may raise the systolic values to 60-80 mm Hg, but the diastolic values and hence the mean arterial pressure still remains inadequate. The use of vasopressor drugs such as epinephrine has been shown to increase blood pressure, as well as the pressure of blood flowing to the heart and the brain, but since heart and brain blood flow relies on adequate diastolic pressures the pressures generated during resuscitation by medical teams, although better than no intervention, are still too low for adequate brain perfusion. It has also been shown that during prolonged periods of cardiac arrest, the pressure inside the brain rises and hence a higher blood pressure is needed to maintain cerebral perfusion. These relatively low blood pressures are maintained during advanced resuscitation until the heart is restarted.
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.
An EEG is a device that is used to measure brain electrical activity
There is severe disorder in the flow of blood to the brain during cardiac arrest