Margaret Beirne

Spectral analysis of electroencephalography in premature newborn infants: Normal ranges

Continuous EEG monitoring has not been used widely in neonatal intensive care, especially in the care of extremely premature infants, probably in part because of a lack of a reliable quantitative method. The purpose of this study was to quantify the EEG of the very premature infants just after birth by using spectral analysis and to describe the characteristics of the spectral signal when infants were clinically stable. Digital EEG recordings were performed on 53 infants who were ≤30 wk gestation for 75 min each day during the first 4 d after birth. Artefact was rejected manually after visual inspection of trace. The EEG was analyzed by manual measurement of interburst interval and automatically by spectral analysis using Fast Fourier Transformation. Spectral analysis generated the normal ranges of the relative power of the δ (0.5–3.5 Hz), θ (4–7.5 Hz), α (8–12.5 Hz), and β (13–30 Hz) frequency bands, spectral edge frequency, and symmetry. The median (range) relative power of the δ band increased significantly from 68% (62–76%) on day 1 to 81% (72–89%) on day 4 (p = 0.001). The interburst intervals became progressively shorter between days 1 [14s (10–25)] and 3 [8s (6–12)]; there were no significant differences between days 3 and 4. The relative power of the δ band seemed to be the most useful and repeatable spectral measurement for continuous long-term monitoring. However, automatic artefact rejection software needs to be developed before continuous quantitative EEG monitoring can be used in the neonatal intensive care environment.

Photosensitivity in juvenile myoclonic epilepsy

Photosensitivity is reported to occur in approximately 40% of patients with juvenile myoclonic epilepsy. Our experience suggests that the prevalence is higher and may be related to both the duration of intermittent photic stimulation and also the age at which the procedure is undertaken. A two-year retrospective review of all EEGs was undertaken on all children attending a paediatric EEG department to identify those with juvenile myoclonic epilepsy. Photosensitivity was defined as a generalized spike or spike-wave paroxysm occurring at least twice during intermittent photic stimulation. Sixty-one children with a diagnosis of juvenile myoclonic epilepsy with a median age of 13 (range 7-16) years were identified, 55 (90%) of whom were photosensitive. Eighteen of these 55 patients showed photosensitivity only after four minutes of continuous photic stimulation. The prevalence of photosensitivity in juvenile myoclonic epilepsy is likely to be higher than previously reported. When a diagnosis of juvenile myoclonic epilepsy is being considered, the initial diagnostic EEG should include intermittent photic stimulation for up to five minutes, or less if the patient shows evidence of photosensitivity. The identification of photosensitivity may have important management implications.

Relationship between blood pressure, cerebral electrical activity, cerebral fractional oxygen extraction, and peripheral blood flow in very low birth weight newborn infants.

There is uncertainty about the level of systemic blood pressure required to maintain adequate cerebral oxygen delivery and organ integrity. This prospective, observational study on 35 very low birth weight infants aimed to determine the mean blood pressure (MBP) below which cerebral electrical activity, peripheral blood flow (PBF), and cerebral fractional oxygen extraction (CFOE) are abnormal. Digital EEG, recorded every day on the first 4 d after birth, were analyzed a) by automatic spectral analysis, b) by manual measurement of interburst interval, and c) qualitatively. CFOE and PBF measurements were performed using near-infrared spectroscopy and venous occlusion. MBP was measured using arterial catheters. The median (range) of MBP recorded was 32 mm Hg (16–46). The EEG became abnormal at MBP levels below 23 mm Hg: a) the relative power of the delta (0.5–3.5 Hz) frequency band was decreased, b) interburst intervals were prolonged, and c) all four qualitatively abnormal EEG (low amplitude and prolonged interburst intervals) from four different patients were recorded below this MBP level. The only abnormally high CFOE was measured at MBP of 20 mm Hg. PBF decreased at MBP levels between 23 and 33 mm Hg. None of the infants in this study developed cystic periventricular leukomalacia. One infant (MBP, 22 mm Hg) developed ventricular dilatation after intraventricular hemorrhage. The EEG and CFOE remained normal at MBP levels above 23 mm Hg. It would appear that cerebral perfusion is probably maintained at MBP levels above 23 mm Hg.

The Relationship between Cardiac Output, Cerebral Electrical Activity, Cerebral Fractional Oxygen Extraction and Peripheral Blood Flow in Premature Newborn Infants

Cardiac output is a determinant of systemic blood flow and its measurement may therefore be a useful indicator of abnormal hemodynamics and tissue oxygen delivery. The purpose of this study was to investigate in very premature newborn infants the relationships between cardiac output (left and right ventricular outputs), systemic blood pressure, peripheral blood flow (PBF) and two indicators of cerebral oxygen delivery (cerebral electrical activity and cerebral fractional oxygen extraction (CFOE)). This was a prospective observational study performed on 40 infants of less than 30 wk gestation. Digital electroencephalograms (EEGs) were recorded for one hour every day during the first four days after birth and subjected to qualitative and quantitative analysis. Left and right ventricular outputs, mean blood pressure (MBP), CFOE, PBF and arterial blood gases were measured at the same time. Within the ranges studied, there was no apparent relationship between left or right ventricular output (RVO), PBF and indicators of cerebral perfusion (cerebral electrical activity and CFOE). The EEG was normal in infants with low left and right ventricular outputs (<150 mL/kg/min) and MBP > 30 mm Hg. Infants with low cardiac output and normal MBP seem able to maintain cerebral perfusion, possibly through vasodilatation of the cerebral microvasculature.

Absence epilepsy in children: the role of EEG in monitoring response to treatment

We report the use of repeat electroencephalography (EEG) in the management of 69 patients with childhood-onset absence epilepsy (CAE). Electro-clinical absences were demonstrated in seven children who were felt clinically to have persisting absences. In three of the remaining 62 patients who were thought to be seizure-free, repeat EEG showed electro-clinical absences; revision of AEDs in these three children resulted in clinical and EEG control. EEG is a useful adjunct to the (usual) subjective monitoring of the response to treatment, and should be repeated routinely in all patients with CAE.

An audit of ambulatory cassette EEG monitoring in children

This audit evaluated the role and usefulness of ambulatory cassette EEG recordings without simultaneous video monitoring in children with paroxysmal episodes including epilepsy. Fifty-four children underwent ambulatory EEG recordings for 48 hours over a 12 month period. Only 31 of the 54 children experienced one of their typical clinical episodes during their recordings. Fifteen of these 31 patients were considered to have epilepsy, only three of whom had a clinical episode at the time of their recording and in all three the EEG demonstrated abnormal (generalized spike and slow wave or focal, rhythmic slow wave) activity. All 10 patients who were considered to have non-epileptic episodes showed no electrical change during their EEG recordings. The results of the ambulatory cassette EEG recordings were considered to have been helpful and to have contributed to the management of only 17 (31%) of the 54 patients in this audit. Stricter clinical criteria for undertaking ambulatory recordings and improved technology are likely to increase the role and usefulness of this procedure.

Abstract of papers and posters presented at ‘Epilepsy1998—The Leading Edge’ annual scientific meeting of the British Branch of the International League against Epilepsy, Oxford, October 1998Photosensitivity in juvenile myoclonic epilepsy

A 30-year-old man with mild learning disability (IQ:72) and cerebral palsy with mild generalized choreoathetosis was referred with paroxysmal motor disorder and episodic depressive mood disorder. Aged 11 months, he had developed episodes of alternating flaccid hemiparesis followed by episodes when he was unable to move or talk but remaining conscious lasting from several minutes to longer. Episodes could be precipitated by excitement such as opening Christmas presents or, later, his favourite football teams scoring a goal or losing. His longest interictal period had been 4 weeks. There was a family history of epilepsy. His EEG aged 6 showed paroxysmal spike and slow waves but no change during episodes of weakness. There was no improvement with phenobarbitone or phenytoin. Aged 1 I, oculogyric crises started during episodes. Aged 19, the EEG showed photosensitivity but was otherwise normal. Episodes were made worse with Sinemet or amphetamines. From age 20, he regularly needed 2 to 5 days a month off work because of episodes. From age 27, episodes could be followed by depression lasting days to months, including suicidal attempts such as swallowing bleach aged 29. Once started on carbamazepine 400 mgs daily, he still had episodes every 2 weeks but has not needed any further time off work, has had no further depressive episodes and is now able to live independently. He could still have rare episodes lasting up to 3 days such as when England won at Wembley.