Burst suppression on an electroencephalogram (EEG) describes a distinctive pattern of brain activity. It involves periods of high-amplitude electrical activity alternating with periods of very low or nearly flatline activity. This pattern is often observed in states of profound brain inactivation.
What is Burst Suppression on an EEG?
An electroencephalogram, or EEG, is a medical test that measures the electrical activity produced by your brain cells. Small metal discs, called electrodes, are placed on the scalp to detect these tiny electrical charges. These charges, which represent the communication between brain cells, are then amplified and appear as wavy lines on a computer screen or printout.
The “burst” phase of burst suppression refers to periods of high-voltage, mixed-frequency electrical activity. These bursts last for 1 to 10 seconds, with amplitudes ranging from 75 to 250 microvolts. Think of it like a sudden, intense burst of static on a radio, followed by silence.
Following each burst is the “suppression” phase, characterized by periods of very low amplitude or near-flatline activity, less than 5 microvolts. The duration of these suppression periods can be longer, exceeding 10 seconds. This alternating pattern reflects a profound reduction in overall brain activity.
When Does Burst Suppression Occur?
Burst suppression is observed in various medical situations, both when intentionally induced and when it occurs spontaneously. It is associated with a deep state of brain inactivity.
One common induced state is deep general anesthesia, where specific medications like propofol or barbiturates are used to significantly reduce brain metabolic activity. This protects the brain during complex surgeries, such as those involving circulatory arrest. The pattern can be adjusted by changing the anesthetic infusion rate.
Burst suppression can also occur spontaneously in severe brain injuries, including traumatic brain injury, anoxic brain injury (due to lack of oxygen), and stroke. In these situations, the brain’s metabolic rate is reduced. Additionally, therapeutic hypothermia, where the body’s temperature is significantly lowered, induces burst suppression, which protects the brain from damage. This pattern is also seen in certain rare conditions like Ohtahara syndrome, an early infantile epileptic encephalopathy.
Why is Burst Suppression Monitored?
Monitoring burst suppression provides real-time insights into the level of brain activity and helps guide treatment decisions.
During general anesthesia, monitoring burst suppression helps clinicians guide the depth of anesthesia. By observing the pattern, medical teams can adjust anesthetic agents to ensure adequate brain protection, particularly during procedures where brain oxygen supply might be compromised. This helps prevent both inadequate anesthesia, which could lead to awareness, and excessive depth.
In critically ill patients, monitoring burst suppression helps assess the severity of brain dysfunction. Its presence indicates inactivation of the brain, aiding in evaluating the patient’s neurological state. This monitoring can also help track the effectiveness of neuroprotective treatments aimed at reducing brain activity, such as in cases of uncontrolled intracranial pressure or severe seizures.
Implications of Burst Suppression
The presence of burst suppression on an EEG carries different implications depending on the clinical context. When induced intentionally, such as during deep general anesthesia or for therapeutic purposes, it represents a desired and protective state. For example, in cases of refractory status epilepticus, induced burst suppression aims to halt seizure activity and protect the brain from further damage.
Spontaneous burst suppression, however, indicates severe brain injury or dysfunction. In conditions like anoxic brain injury following cardiac arrest, it is associated with a poorer neurological outcome. Some studies suggest a neuroprotective effect of sedation-induced burst suppression in traumatic brain injury, but its interpretation always depends on the patient’s overall condition and the underlying cause. The pattern’s persistence, especially with identical bursts, is a strong indicator of an unfavorable prognosis in certain severe brain injuries.