Brain monitoring in neonates
Section snippets
Amplitude integrated aEEG (aEEG)
Dr. Douglas Maynard constructed the cerebral function monitor (CFM) in the late 1960s for continuous EEG monitoring. His colleague Dr. Pamela Prior later developed the clinical application, mainly for adult patients during anaesthesia and intensive care, after cardiac arrest, during status epilepticus and after heart surgery. The term amplitude integrated EEG (aEEG) is currently preferred to denote a method for encephalographic monitoring while CFM is used to refer to a specific device. The EEG
Assessment of aEEG background pattern [1]
The aEEG traces are assessed visually based on pattern recognition and classified into the five following categories in full-term infants (Fig. 1):
- a)
the continuous normal voltage pattern (CNV) is a continuous trace with a voltage 10–25 (− 50) μV (Fig. 1a)
- b)
discontinuous normal voltage pattern (DNV) is a discontinuous trace, where the low voltage is predominantly above 5 μV (no burst suppression) (Fig. 1b)
- c)
discontinuous background pattern (burst suppression): periods of low voltage (inactivity)
aEEG in neonatal encephalopathy
The value of the background pattern in the prediction of neurodevelopmental outcome has already been established with the use of the standard EEG. A poor background pattern, persisting beyond the first 12–24 h after birth (burst suppression (BS), low voltage and flat trace), is well known to carry a poor prognosis. There have been several studies where aEEG and standard EEG were performed simultaneously to compare the two techniques. Overall there appeared to be a good correlation between the
Detection of epileptic seizure activity
Seizure burden is known to be very high in encephalopathic neonates. A recent video-conventional EEG study by Murray et al. [11] shows that only one third of neonatal EEG seizures display clinical signs on simultaneous video recordings. Two-thirds of these clinical manifestations are unrecognised or misinterpreted by experienced neonatal staff. Clinical diagnosis is therefore not sufficient for the recognition and management of neonatal seizures.
A rapid rise of both the lower and the upper
Pitfalls and artefacts
One can either use a classification system based on pattern recognition (see above) or look at actual values of lower and upper margins of activity (al Naqeeb criteria [5]), i.e. normal amplitude (maximum amplitude > 10 μV, minimum amplitude > 5 μV); moderately abnormal (maximum amplitude > 10 μV, minimum amplitude ≤ 5 μV) and severely abnormal (maximum amplitude < 10 μV, minimum amplitude < 5 μV). Although one would be inclined to prefer values, rather than patterns, values may be misleading, as
Seizure like artefacts
Any movement or handling of the baby, with a sudden increase of the baseline of the aEEG recording, can also mimic seizure activity on the aEEG. The simultaneous recorded single channel “real” EEG signal can help to interpret aEEG traces more accurately. In addition marking events on the aEEG recording by nursing staff is very important.
aEEG in preterm infants
aEEG is also feasible for monitoring cerebral activity in preterm infants during intensive care. In parallel with multichannel EEG, aEEG background activity is more discontinuous in preterm infants. Normative values for aEEG background activity at different gestational ages have been published [15]. A scoring system for evaluation of brain maturation in neonates has also been developed [16]. Sleep–wake cycling can be clearly identified in the aEEG from around 30 weeks gestation, but also at
Near Infrared Spectroscopy (NIRS)
The use of in vivo NIRS in humans was already introduced in the late seventies for non-invasive monitoring of tissue oxygenation. It has been used mainly as a research tool in premature infants and term infants with perinatal asphyxia and in open heart surgery.
In these studies changes in oxygenated haemoglobin (O2Hb) and deoxygenated haemoglobin (HHb) as measures of cerebral oxygenation, as well as changes in total haemoglobin (THb) and/or the difference between O2Hb and HHb (Hb-D) were used.
Clinical applications of NIRS
The most important issue regarding clinical application of NIRS-monitored cerebral oxygenation and saturation is the ability to perform reliable and non-invasive long-term monitoring of cerebral oxygenation in the most immature and unstable neonates without the necessity to frequently disturb the infant. The most critical part here is appropriate fixation to the skull of the transducer, which contains the light emitting diode and the distant sensors (reflection method), to allow reliable
Guidelines for aEEG-monitoring
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Perinatal asphyxia
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Cooling
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Neonatal seizures and/or apneas
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Metabolic disorders
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Meningoencephalitis
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Post-surgery, especially cardiac surgery
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Muscle paralysis
Research directions for aEEG-monitoring
Fullterm infant:
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Seizure detection
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Effect of intervention (cooling) on recovery of background patterns and seizure onset
Preterm infant:
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Seizure detection
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Other modalities of background pattern evaluation; i.e. inter burst duration
Older infants (analysis of more than one channel/frequency):
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Cardiac surgery
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Neurosurgery
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Near drowning
Guidelines for NIRS-monitoring
(rSO2, FTOE or TOI simultaneous with blood pressure and arterial saturation)
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Critically ill patients
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Hypotension
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PDA
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Prenatal asphyxia
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Cardiac surgery
Research directions for NIRS
(Absolute) normative values for rSO2, FTOE and TOI
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at different gestational ages and time after birth
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during cooling or other neuroprotective interventions
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during seizures
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