TOBY - neoweb.org.uk

1 CerebralFunctionMonitoringAddition to CFM handbook forusers of the Olympic CFM 6000 TOBYISRCTN 89547571 2 The contents of this booklet wereoriginally produced for the Azzopardi Copyright: Denis Azzopardi 16/06/04 3 ContentsPageOverview4 Interpreting the CFM trace4 CFM vs EEG5 Classification of the CFM5 Attaching the electrodes7 Self adhesive electrodes7 Needle electrodes7 Equipment and brief operating instructions8 Sample traces8-25 Index of features in tracesSample numbersNormal traces with sleep/wake cycling1, 2.

2 3, background with seizures15, abnormal traces5, 7, 8, 9, 11, 12, 13, abnormal traces6, 7, 12, 13, 18, 19, 22,23, 25, 26, 29, 30, 31, , 14, 16, 17, 26, 27, 28,29, 30, 32, suppression7, 12, artefact1, 8, artefact21, 23, EEG18, 19, 22, , of medication11, 14, ManualOlympic 6000 Cerebral Function Monitor 4 EQUIPMENTO verviewThe Olympic CFM 6000 records a single channel of EEG recorded from 2electrodes placed on either side of the head. A third electrode acts as aground.

3 The signal is filtered and rectified and the range of amplitude ofthe signal in microvolts is displayed on the monitor at 6 cms per hour. Thismakes every major division of the CFM trace equal to 10 minutes of <2 and >15 Hz are selectively filtered to reduce artefactscaused by movement, ECG and other electronic equipment. The CFM6000 stores the underlying EEG allowing inspection of the unprocessedEEG at any point in the CFM trace, which helps in identifying artefacts andconfirming seizure the CFM traceThe CFM trace consists of a dense trace that can vary in width.

4 Twofeatures of the trace should be assessed: the amplitude of the trace, andthe presence of seizure activity. The amplitude of the trace can beassessed by measuring the upper and lower margins of the trace againstthe scale shown on the monitor or printed on the printer paper. Whenmeasuring the amplitude of the CFM it is the dense trace of EEG activity 5that is measured; the brief spikes that can sometimes be seen outside thedense trace are ignored.

5 The position of the margins of the trace canusually be eyeballed, or a ruler can be used to draw a line along themargin of the are characterised by sudden rise and narrowing of the trace(reflecting the increase in EEG voltage). The trace returns to the previousappearance when the seizure activity stops. Inspection of the underlyingEEG helps confirm the occurrence of seizures on the CFM trace. Theunderlying EEG usually shows a repetitive spike and wave discharge butother EEG seizure patterns may be seen.

6 Seizures may only be identifiedif they are sufficiently prolonged, more than 2-3 minutes. Shorter lastingdischarges may be missed since the CFM is recorded at a very slowspeed. It may be difficult to distinguish burst suppression from briefseizures in a severely abnormal trace but the distinction can be made byinspecting the underlying EEG. It may not be possible to comment on thebackground amplitude of the CFM trace if seizures are very vs EEGS ince the CFM records the amplitude of the EEG at a very slow speed,continuous EEG activity is manifest on the CFM as a dense trace varyingfrom about 10-40 microvolts.

7 The width of the trace varies with the state ofthe infant. The trace is wider during quiet sleep and narrower in activesleep or when awake. Discontinuity of the EEG results in a wider tracebecause of a fall of the lower margin of the trace. The more discontinuousthe EEG activities the wider the CFM trace. Severely disorganised EEGactivity such as burst suppression is manifest as a narrower lower voltageCFM trace accompanied by bursts of higher voltage activity. Very lowvoltage EEG will be displayed as a very narrow CFM trace usually with thelower margin of the trace very close to the of the CFMA simple semiquantitative classification is used in the toby upper margin of the trace is above 10 microvolts and the lowermargin is greater than 5 healthy full term infants the trace alters in width according to thestate of the infant.

8 The trace is narrower when the infant is awakeand widens during sleep. These changes in width of the trace withinfant state are called sleep/wake cycling. In normal infants the widthof the trace varies from approximately 10-40 microvolts. abnormalThe upper margin of the trace is greater than 10 microvolts andthe lower margin is less than 5 appearance can be seen in infants with moderately severeencephalopathy, or immediately after administration of drugs such asanticonvulsants and sedatives.

9 This pattern may also be seen inpreterm infants (below 36 weeks gestation). abnormalThe upper margin of the trace is less than 10 microvolts. The lowermargin is usually less than 5 microvolts but on occasion the lowermargin may be raised above 5 microvolts because of interferencefrom ECG or other severely abnormal trace is characterised by a general suppressionof amplitude so that the trace appears narrow and of low pattern may be accompanied by brief bursts of higher voltagespikes, which appear as single spikes above the background appearance is sometimes called burst suppression.

10 A severelyabnormal trace is usually seen with severe encephalopathy and isoften accompanied by seizure to Note The CFM does not give information about EEG frequency. It onlydisplays the amplitude of the EEG. EEG activity less than 2 Hz or greater than 12 Hz is not recorded bythe CFM trace. Focal abnormalities in the EEG may not be identified because thesignal is obtained from a single channel. If the CFM trace looks odd or is not consistent with the clinical pictureuse the EEG display facility on the CFM 6000 to check for artefacts.