Overview

• One out of five patients wake up with a new neurologic deficit after cardiac surgery 
• 6% of cardiac bypass patients have a stroke 
• Cerebral stroke is #3 killer and #1 cause for adult disability 
• 10 to 60% of ICU patients suffer from seizures. Majority of ICU seizures are non con-convulsive; not detectable without EEG 
• Seizures are progressing and are in a risk of developing into status epileptics. Status epileptics causes irreversible damage to the brain causing increased morbidity and mortality

Brain functions are vital functions just as cardiac functions; failures in brain functions have severe consequences

In the ICU

• Detection of seizures
• Detection of ischemia/hypoxia
• Prognosis of an unconscious patient (reactivity, sleep cycles)
• Monitoring the seizure treatment efficacy
• Monitoring the level of burst suppression ration during e.g propofol treatment of status epilepticus
• Prognosis of comatose patient (for instance, burst suppression in head trauma indicated poor prognosis)

In the OR

• Brain oxygenation -> early warning for brain ischemia
• Asymmetry (carotid surgery)
• Hypothermia in heart surgery (isoelectric activity)
• Fast detection of epileptiform activity and developing asymmetries

Alpha waves (8 – 13 Hz)  

Waking state of the normal adult 

Predominant in drowsiness. Theta and alpha are equally dominant in children but as children get older, theta decreases and becomes more intermittent  

Beta EEG (14 – 30 Hz) 

Predominant in drug-induced sleep from barbiturates, with therapeutic levels of antidepressants and with the majority of benzodiazepines, such as Valium  

Delta EEG (0.5 – 3 Hz) 

Primary frequency found in the sleeping adult  

Burst suppression EEG 

This abnormal pattern can be seen following cardiac arrest and anesthesia and/or barbiturate intoxication 

Seizure activity

This pattern is suggestive of epilepsy. Most seizures in the ICU are silent and can only be detectable with EEG  

PLEDS (Periodic Lateralized Epileptiform discharges) 

Transient pattern often seen following a cardiac arrestor respiratory event

AEP represents the electrical activity to auditory stimulus. 

AEP monitoring

• AEP measurement includes headphones for delivering the auditory stimulus 
• Stimulation (clicks) to the ear 
• Measurement above the auditory cortex 
• Hidden under spontaneous EEG

Importance of AEP Monitoring

In the ICU

• Assessment of neurological status
• L-T changes in the central nervous system
• Brain stem responses for prognosis of coma
• Automated, integrated measurement
• Monitoring coma/poisoning patients

In the OR

• Neurosurgical applications
• Protection of auditory nerves
• Operations close to the brain stem
• Automated, integrated measurement
• Assessing never protection (auditory nerves and the Facialis nerve) and the protection of brain stem
• Beneficial also e.g. in posterior fossa surgery and microvascular decompression 
• Ensuring complete deep hypothermic electrocerebral silence prior to temporary circulatory arrest
• Ventricular endoscopies