CEREBRAL FUNCTION MONITORING

BYAHMED GALAL OKASHA

AL JAHRA NICU

Cerebral Function Monitor (CFM),or An amplitude-integrated EEG, is a device used to measure background electrocortical activity in the brain.

The cerebral function monitor provides information on global cerebral activity. to indicate the generalized level of electrical activity occurring across the entire brain.

CFM technology was initially developed in the 1960s for adults suffering from neurological depression or injury or undergoing surgery.

technology was introduced in the mid 1980s by neonatologists. Research showed it could be a sensitive tool for predicting severity of hypoxic-ischemic encephalopathy, if applied in the first 6–12 hours following perinatal asphyxia.

this mean it has predictive value on acute neurological conditions and long term neurodevelopmental outcome.

The CFM has also demonstrated itself as a valuable detection tool for neonates with clinical or subclinical seizures.

Intended use of CFMContinuous monitoring and recording of

brain activity.Aiding detection and treatment of siezures.Monitor the effect of the drugs and other

therapy in the brain.Aiding in identifying the HIE and

predicting the long- term outcome.Improving the accuracy of neonatal

neurological examination

Indications:

• Hypoxic – Ischemic Encephalopathy • Seizures or clinical scenario mimicking seizure

disorders (e.g., apnea, hypertension, tachycardia) • Significant neurological disorders (e.g.,

congenital brain malformations, vascular lesions) • Post cardiac arrest • Inborn error of metabolism (e.g., urea cycle

disorders, hypoglycaemia, hypocalcaemia) • Neonatal abstinence syndrome (e.g.,

alcohol/opiate withdrawal)

Principle of CFM

Using a single lead (single channel), consisting of three wires placed over the biparietal or frontal region;

the machine filters, rectifies and

compresses the electric brian signal.

Filtering and rectifying mean Frequencies <2 and >15 Hz are

selectively filtered to reduce artefacts caused by movement, ECG and other electronic equipment.

Compression mean time compression The signal is

displayed on an x-y axis, using a very slow chart speed (6 cm/h).

The CFM focuses on changes in amplitude in the EEG — it is referred to as aEEG — amplitude-integrated EEG.

The amplitude of the trace can be assessed by measuring the upper and lower

margins of the trace against.

Applying electrodes

Placement• Biparietal is the optimal location this is

the watershed area between the posterior and middle cerebral arteries. This area is least likely to be affected by scalp muscle activity and eye-movement artifacts.

ImpedanceMeasures quality of electrode contact and

should beas low as possible. It is also used to detect lead

motion artifact.The CFM 6000 monitor will Alarm if > 20kΩ.

Hydrogel electrodes — can be used on scalp (biparietal) or forehead Requires aggressive preparation for cleaning to assure adequate adherence. These electrodes should be replaced every 24 hours.

Low-impedance needle electrodes Insert sub-dermally in parietal position

These electrodes can be left in place for days, if needed.

General interpretation

• Presence of Sleep/Wake cycle• Amplitudes of the upper and lower margins of

the trace — in micro-voltage (μV)• Variability — narrow or broad trace.• Brain ActivityContinuous (normal) — dark central band of

continuous activity, with normal amplitudesDiscontinuous (abnormal) — a wide trace with no

central band of activity; appears universally gray• Presence of seizure activity

• Continuous normal voltage (CNV) — a narrow band on the aEEG with dark central band indicating a continuous normal high level of activity with little variability

Discontinuous normal voltage (DNV) — a wide band on the aEEG that appears universally gray, indicating increased variability in activity primarily due to intermittent lower levels of activity

Understanding aEEG

Quiet/active cycling — also known as sleep/wake cycle — trace is narrow when infant is awake (or in active sleep) and widens during quiet sleep; typically cycles every 90 min, but is dependent on infant condition. Early return of sleep wake cycling (SWS) after an asphyxial insult is also a good prognostic sign.

• Flat EEG — a relatively flat trace at the bottom of the aEEG scale

Burst suppression (BS) — a comb like pattern in the aEEG due to

A severely abnormal trace is characterised by a general suppression of amplitude so that the trace appears narrow and of low voltage.

may be accompanied by brief bursts of higher voltage

spikes, which appear as single spikes above the background activity.

usually seen with severe encephalopathy and often accompanied by seizure activity.

seizures can be detected if there is sudden(rising

and narrowing) in the aEEG. Status epilepticus = continuous seizures ≥

30 min.

It is important to inspect the underlying EEGto confirm the presence of seizures .distinguish artifacts from real signal.

underlying EEG usually shows a repetitive spike and wave discharge .

Seizures may only be identified if they are sufficiently prolonged, more than 2-3 minutes. Shorter lasting discharges may be missed since the CFM is recorded at a very slow speed.

Classification of the CFM

1. NormalThe upper margin of the trace is above 10

microvolts and the lower margin is greater than 5 microvolts.

sleep/wake cycling. the width of the trace varies from

approximately 10-40 microvolts.

Normal CFM voltage. Sleep wake cycling can be observed.Movement artefact is present in part of trace.

2. Moderately abnormal The upper margin of the trace is greater than

10 microvolts and the lower margin is less than 5 microvolts. No SWC.

This appearance can be seen in infants with:moderately severe encephalopathy.immediately after administration of drugs

such as anticonvulsants and sedatives. This pattern may also be seen in preterm

infants (below 36 weeks gestation).

Severely abnormalThe upper margin of the trace is less than 10

microvolts. The lower margin is usually less than 5 microvolts

Presence of burst suppression spikes.No sws.(FLAT TRACE) seen with severe encephalopathy and often

accompanied by seizure activity.

Scoring Prediction of HIE Outcome and

Points to Note Focal abnormalities in the EEG may not be

identified because the .signal is obtained from a single channel.

If the CFM trace looks odd or is not consistent with the clinical picture use the EEG display facility on the CFM to check for artefacts.

Movement artefact associated with head bobbing due to breathing

position of the head or supporting the head with a roll may lessen the artefact.

Pulse artefact may be difficult to distinguish from seizure on the EEG. The pulse artefact is regular with the pulse. Place the electrode away from the fontanelle may help.

Medications may affect the record. Anticonvulsants or sedatives such as morphine or chloral hydrate may transiently suppress the CFM record. So Administration of drugs or other clinical events should be marked to

Pitfalls to watch for

• Background voltage appears elevated — Possible causes:

• ECG artifact• Handling• Muscle activity• High-frequency ventilation• Status epilepticus• Gasp artifact• Background voltage appears depressed — Possible

causes:• Severe scalp edema• Leads significantly too close together• Significant sedation