Early neurophysiology and MRI in predicting neurological outcome at 9-10 years after birth asphyxia

Continous somatosensory evoked potentials and brain injury in neonatal hypoxic-ischaemic encephalopathy treated with hypothermia

AIM

To explore whether continuous somatosensory evoked potentials (SEPs) monitoring and video electroencephalograms (VEEG) accurately predict lesions observed on brain magnetic resonance imaging (MRI) in neonates with hypoxic-ischaemic encephalopathy (HIE) receiving therapeutic hypothermia.

METHOD

This prospective study included 31 neonates (16 males, 15 females; mean [SD] gestational age 39 weeks [1.67]) who received therapeutic hypothermia for HIE. Therapeutic hypothermia was provided for 72 hours, with a target temperature of 33.0°C to 34.0°C and this was followed by a rewarming rate of approximately 0.5°C per hour, up to 36.5°C. SEPs and VEEG were evaluated simultaneously and continuously for 1 hour under normothermic conditions. MRI was carried out at a mean (SD) age of 6 (2) days.

RESULTS

Our results showed a statistically significant correlation between continuous SEP and MRI scores (r=0.37, p=0.03), but not between the VEEG and MRI scores (r=0.30, p=0.09). Receiver operating characteristic analysis confirmed that continuous SEPs were highly specific and sensitive at predicting MRI abnormalities, whereas the VEEG had high specificity but low sensitivity.

INTERPRETATION

Continuous monitoring of SEPs could provide early and important prognostic information in neonates with HIE.

WHAT THIS PAPER ADDS

Early continuous somatosensory evoked potential (SEP) monitoring is correlated with hypoxic-ischaemic encephalopathy (HIE) lesions. Video electroencephalograms (VEEGs) are associated with lesions diagnosed after magnetic resonance imaging. Both showed high specificity, but VEEGs did not show high sensitivity. Continuously monitoring SEPs provides important information about HIE.

Neonates with mild hypoxic-ischaemic encephalopathy receiving supportive care versus therapeutic hypothermia in California

OBJECTIVE

The use of therapeutic hypothermia (TH) for mild hypoxic-ischaemic encephalopathy (HIE) remains controversial and inconsistent. We analysed trends in TH and maternal and infant characteristics associated with short-term outcomes of infants with mild HIE.

DESIGN

Retrospective cohort analysis of the California Perinatal Quality Care Collaborative database 2010-2018. E-value analysis was conducted to determine the potential impact of unmeasured confounding.

SETTING

California neonatal intensive care units.

PATIENTS

1364 neonates with mild HIE.

INTERVENTIONS

Supportive care versus TH.

MAIN OUTCOME MEASURES

Factors associated with TH and mortality.

RESULTS

The proportion of infants receiving TH increased from 46% in 2010 to 79% in 2018. TH was more likely in the setting of singleton birth (OR 2.69, 95% CI 1.21 to 5.39), no major birth defects (OR 2.18, 95% CI 1.42 to 3.30), operative vaginal delivery (OR 3.04, 95% CI 1.80 to 5.10) and 5-minute Apgar score ≤5 (OR 3.17, 95% CI 2.43 to 4.13). Mortality was associated with small for gestational age (OR 5.79, 95% CI 1.90 to 18.48), <38 weeks' gestation (OR 7.31 95% CI 2.39 to 24.93), major birth defects (OR 11.62, 95% CI 3.97 to 38.00), inhaled nitric oxide (OR 12.73, 95% CI 4.00 to 44.53) and nosocomial infection (OR 7.98, 95% CI 1.15 to 47.03). E-value analyses suggest that unmeasured confounding may have contributed to some of the observed effects.

CONCLUSIONS

Variation in management of mild HIE persists, but therapeutic drift has become more prevalent over time. Further studies are needed to assess long-term outcomes alongside resource utilisation to inform evidence-based practice.

Abnormalities in evoked potentials associated with abnormal glycemia and brain injury in neonatal hypoxic-ischemic encephalopathy

OBJECTIVE

To investigate how functional integrity of ascending sensory pathways measured by visual and somatosensory evoked potentials (VEP & SEP) is associated with abnormal glycemia and brain injury in newborns treated with hypothermia for hypoxic-ischemic encephalopathy (HIE).

METHODS

Fifty-four neonates ≥ 36 weeks gestational age with HIE underwent glucose testing, VEPs, SEPs, and magnetic resonance imaging (MRI) the first week of life. Minimum and maximum glucose values recorded prior to evoked potential (EP) testing were compared with VEP and SEP measures using generalized estimating equations. Relationships between VEP and SEP measures and brain injury on MRI were assessed.

RESULTS

Maximum glucose is associated with decreased P200 amplitude, and increased odds that N300 peak will be delayed/absent. Minimum glucose is associated with decreased P22 amplitude. Presence of P200 and N300 peaks is associated with decreased odds of brain injury in the visual processing pathway, with delayed/absent N300 peak associated with increased odds of brain injury in posterior white matter.

CONCLUSIONS

Deviations from normoglycemia are associated with abnormal EPs, and abnormal VEPs are associated with brain injury on MRI in cooled neonates with HIE.

SIGNIFICANCE

Glucose is a modifiable risk factor associated with atypical brain function in neonates with HIE despite hypothermia treatment.

Cortical responses to tactile stimuli in preterm infants

The conventional assessment of preterm somatosensory functions using averaged cortical responses to electrical stimulation ignores the characteristic components of preterm somatosensory evoked responses (SERs). Our study aimed to systematically evaluate the occurrence and development of SERs after tactile stimulus in preterm infants. We analysed SERs performed during 45 electroencephalograms (EEGs) from 29 infants at the mean post-menstrual age of 30.7 weeks. Altogether 2,087 SERs were identified visually at single-trial level from unfiltered signals capturing also their slowest components. We observed salient SERs with a high-amplitude slow component at a high success rate after hand (95%) and foot (83%) stimuli. There was a clear developmental change in both the slow wave and the higher-frequency components of the SERs. Infants with intraventricular haemorrhage (IVH; eleven infants) had initially normal SERs, but those with bilateral IVH later showed a developmental decrease in the ipsilateral SER occurrence after 30 weeks of post-menstrual age. Our study shows that tactile stimulus applied at bedside elicits salient SERs with a large slow component and an overriding fast oscillation, which are specific to the preterm period. Prior experimental research indicates that such SERs allow studying both subplate and cortical functions. Our present findings further suggest that they might offer a window to the emergence of neurodevelopmental sequelae after major structural brain lesions and, hence, an additional tool for both research and clinical neurophysiological evaluation of infants before term age.

Association of cerebral activity with MRI scans in infants with neonatal encephalopathy undergoing therapeutic hypothermia

We aimed to correlate amplitude-integrated EEG (aEEG) in neonatal hypoxic ischemic encephalopathy (HIE) with early magnetic resonance imaging (MRI). In this retrospective study, 32 neonates over 35 weeks' gestation with moderate/severe HIE who were treated with hypothermia were included. Early MRI scans and daily aEEG background were categorized to mild/normal, moderate, and severely abnormal. Time to sleep cycling was noted on aEEG. Mantel-Haenszel test for trends was used to explore associations between aEEG and MRI and outcome. LOESS regression was used for exploring the association of cycling with MRI scores. MRI was normal/mildly abnormal in 20 (63%) infants; in 9 (28%), moderately abnormal; and in 3 (9%), severely abnormal. Twenty-seven (84%) infants s urvived. MRI severity score was significantly associated with aEEG background score on the third and fourth days of life (p < 0.01). An increase in the MRI severity score was noted if sleep cycling appeared after the fifth day of life.Conclusions: Depressed aEEG at the third and fourth days of life and appearance of cycling beyond the fifth day of life are associated with cerebral MRI abnormalities and may be associated with increased risk of abnormal outcome. What is known: • Since therapeutic hypothermia has been shown to change long-term outcome, amplitude-integrated EEG in infants with hypoxic ischemic neonatal encephalopathy soon after birth have a limited predictive power for long-term outcome in treated infants. • Brain MRI after therapeutic hypothermia in the above infants has a significant predictive value for long-term outcome What is new: • Background amplitude-integrated EEG activity depression at the age of 3 and 4 days and delay of appearance of cycling activity are associated with worse MRI scores and may be predictive of worse long-term outcome.

Evoked potentials predict psychomotor development in neonates with normal MRI after hypothermia for hypoxic-ischemic encephalopathy

OBJECTIVES

To assess the prognostic role of evoked potentials (EP) in neonates with normal magnetic resonance imaging (MRI) after therapeutic hypothermia (TH) for hypoxic-ischemic encephalopathy (HIE).

METHODS

Thirty-five neonates recruited for TH because of HIE, having normal neonatal MRI, performed neonatal somatosensory (SEP), visual (VEP) evoked potentials and electroencephalogram (EEG). The effect of SEP, VEP or EEG abnormalities on Griffith's developmental scales at 12 and 24 months was measured; positive (PPV) and negative (NPV) predictive value, sensitivity, specificity and accuracy were calculated.

RESULTS

At 24 months, 28% had global psychomotor impairment and 57% had isolated impairments. VEP abnormality was associated with impaired hearing-language score (p = 0.002) and performance score (p < 0.0001). VEP achieved best PPV (0.91, 95% C.I. 0.62-0.99) and specificity (0.93, 95% C.I. 0.70-0.99). The combination of neurophysiological tests achieved the best NPV (0.85, 95% C.I. 0.58-0.96), sensitivity (0.90, 95% C.I. 0.70-0.97), overall accuracy (0.83, 95% C.I. 0.67-0.92).

CONCLUSIONS

Psychomotor sequelae may occur in survivors of neonatal HIE with normal MRI. VEP is the single best neurophysiological prognostic marker but the combination of neurophysiological tests has a better value.

SIGNIFICANCE

When facing the challenge of neurodevelopmental prognosis in infants with normal MRI after TH, EPs are useful prognostic tools, complementary to EEG.

Multimodal neurophysiological monitoring in healthy infants born at term: normative continuous somatosensory evoked potentials data

AIM

To describe accurate, standardized 1h-multimodal neurophysiological monitoring (1h-MNM), while simultaneously recording VEEG, aEEG, and SEP-C bilaterally from median nerves, and to collect neonatal normative SEP-C data related to behavioural states.

METHOD

Twenty healthy, term newborn infants (13 males, 7 females; gestational age 37-42wks; mean 39.6wks, standard deviation [SD] 1.3wks) underwent 1h-MNM within 2 days of life, with focus on recording of the SEP-C (band-pass setting 1-100 Hz, rate of stimulation 1.1 Hz, 50 alternate stimuli).

RESULTS

1h-MNM was easily obtained with identification of cervical (N13) and cortical (N1, P1) SEP-C responses in all infants. SEP-C minimal and maximum N1 latencies/N1-P1 amplitudes were identified, bilaterally, during periods of spontaneous sleep active-quiet-active (AS-QS-AS) and quiet-wakefulness. Minimal latencies and amplitudes occurred in 60% of active sleep/quiet-wakefulness, with the maximums in 70% of quiet sleep. The SEP-C mean values were latencies of N13=13.6ms (SD 1.4ms) and N1=33.6ms (SD 3.9ms) to 34.2ms (SD 4.8ms) in left and right hemisphere respectively; central-conduction-time (CCT) (N13-N1), 20.0ms (SD 4.3ms) to 20.6ms (SD 4.8ms); N1-P1 amplitude=4.6ms (SD 2.7ms) to 3.8μV (SD 2.2μV).

INTERPRETATION

1h-MNM can record simultaneously VEEG/aEEG/SEP-C in newborn infants, showing the modulation of SEP cortical responses in relation to behavioural states in all infants studied using an appropriate neonatal method. We emphasize the importance of obtaining neonatal SEP-C normative data to better identify pathological findings in neonatal brain injury.

The Frequency and Severity of Magnetic Resonance Imaging Abnormalities in Infants with Mild Neonatal Encephalopathy

OBJECTIVE

To assess and contrast the incidence and severity of abnormalities on cerebral magnetic resonance imaging (MRI) between infants with mild, moderate, and severe neonatal encephalopathy who received therapeutic hypothermia.

STUDY DESIGN

This retrospective cohort studied infants with mild, moderate, and severe neonatal encephalopathy who received therapeutic hypothermia at a single tertiary neonatal intensive care unit between 2013 and 2015. Two neuroradiologists masked to the clinical condition evaluated brain MRIs for cerebral injury after therapeutic hypothermia using the Barkovich classification system. Additional abnormalities not included in this classification system were also noted. The rate, pattern, and severity of abnormalities/injury were compared across the grades of neonatal encephalopathy.

RESULTS

Eighty-nine infants received therapeutic hypothermia and met study criteria, 48 with mild neonatal encephalopathy, 35 with moderate neonatal encephalopathy, and 6 with severe neonatal encephalopathy. Forty-eight infants (54%) had an abnormality on MRI. There was no difference in the rate of overall MRI abnormalities by grade of neonatal encephalopathy (mild neonatal encephalopathy 54%, moderate neonatal encephalopathy 54%, and severe neonatal encephalopathy 50%; P= .89). Basal ganglia/thalamic injury was more common in those with severe neonatal encephalopathy (mild neonatal encephalopathy 4%, moderate neonatal encephalopathy 9%, severe neonatal encephalopathy 34%; P = .03). In contrast, watershed injury did not differ between neonatal encephalopathy grades (mild neonatal encephalopathy 36%, moderate neonatal encephalopathy 32%, severe neonatal encephalopathy 50%; P = .3).

CONCLUSION

Mild neonatal encephalopathy is commonly associated with MRI abnormalities after therapeutic hypothermia. The grade of neonatal encephalopathy during the first hours of life may not discriminate adequately between infants with and without cerebral injury noted on MRI after therapeutic hypothermia.

Evoked potentials recorded during routine EEG predict outcome after perinatal asphyxia

OBJECTIVE

To evaluate the added value of somatosensory (SEPs) and visual evoked potentials (VEPs) recorded simultaneously with routine EEG in early outcome prediction of newborns with hypoxic-ischemic encephalopathy under modern intensive care.

METHODS

We simultaneously recorded multichannel EEG, median nerve SEPs, and flash VEPs during the first few postnatal days in 50 term newborns with hypoxic-ischemic encephalopathy. EEG background was scored into five grades and the worst two grades were considered to indicate poor cerebral recovery. Evoked potentials were classified as absent or present. Clinical outcome was determined from the medical records at a median age of 21months. Unfavorable outcome included cerebral palsy, severe mental retardation, severe epilepsy, or death.

RESULTS

The accuracy of outcome prediction was 98% with SEPs compared to 90% with EEG. EEG alone always predicted unfavorable outcome when it was inactive (n=9), and favorable outcome when it was normal or only mildly abnormal (n=17). However, newborns with moderate or severe EEG background abnormality could have either favorable or unfavorable outcome, which was correctly predicted by SEP in all but one newborn (accuracy in this subgroup 96%). Absent VEPs were always associated with an inactive EEG, and an unfavorable outcome. However, presence of VEPs did not guarantee a favorable outcome.

CONCLUSIONS

SEPs accurately predict clinical outcomes in newborns with hypoxic-ischemic encephalopathy and improve the EEG-based prediction particularly in those newborns with severely or moderately abnormal EEG findings.

SIGNIFICANCE

SEPs should be added to routine EEG recordings for early bedside assessment of newborns with hypoxic-ischemic encephalopathy.

Development of somatosensory-evoked potentials in foetal sheep: effects of betamethasone

AIM

Antenatal glucocorticoids are used to accelerate foetal lung maturation in babies threatened with premature labour. We examined the influence of glucocorticoids on functional and structural maturation of the central somatosensory pathway in foetal sheep. Somatosensory-evoked potentials (SEP) reflect processing of somatosensory stimuli. SEP latencies are determined by afferent stimuli transmission while SEP amplitudes reveal cerebral processing.

METHODS

After chronic instrumentation of foetal sheep, mothers received saline (n = 9) or three courses of betamethasone (human equivalent dose of 2 × 110 μg kg^-1 betamethasone i.m. 24 h apart, n = 12) at 0.7, 0.75 and 0.8 of gestational age. Trigeminal SEP were evoked prior to, 4 and 24 h after each injection and at 0.8 of gestational age before brains were histologically processed.

RESULTS

Somatosensory-evoked potentials were already detectable at 0.7 of gestation age. The early and late responses N20 and N200 were the only reproducible peaks over the entire study period. With advancing gestational age, SEP latencies decreased but amplitudes remained unchanged. Acutely, betamethasone did not affect SEP latencies and amplitudes 4 and 24 h following administration. Chronically, betamethasone delayed developmental decrease in the N200 but not N20 latency by 2 weeks without affecting amplitudes. In parallel, betamethasone decreased subcortical white matter myelination but did not affect network formation and synaptic density in the somatosensory cortex.

CONCLUSION

Somatosensory stimuli are already processed by the foetal cerebral cortex at the beginning of the third trimester. Subsequent developmental decrease in SEP latencies suggests ongoing maturation of afferent sensory transmission. Antenatal glucocorticoids affect structural and functional development of the somatosensory system with specific effects at subcortical level.

Beyond the N1: A review of late somatosensory evoked responses in human infants

Somatosensory evoked potentials (SEPs) have been used for decades to study the development of somatosensory processing in human infants. Research on infant SEPs has focused on the initial cortical component (N1) and its clinical utility for predicting neurological outcome in at-risk infants. However, recent studies suggest that examining the later components in the infant somatosensory evoked response will greatly advance our understanding of somatosensory processing in infancy. The purpose of this review is to synthesize the existing electroencephalography (EEG) and magnetoencephalography (MEG) studies on late somatosensory evoked responses in infants. We describe the late responses that have been reported and discuss the utility of such responses for illuminating key aspects of somatosensory processing in typical and atypical development.

How to use: amplitude-integrated EEG (aEEG)

Amplitude-integrated electroencephalography (aEEG) is a method for continuous monitoring of brain activity that is increasingly used in the neonatal intensive care unit. In its simplest form, aEEG is a processed single-channel electroencephalogram that is filtered and time-compressed. Current evidence demonstrates that aEEG is useful to monitor cerebral background activity, diagnose and treat seizures and predict neurodevelopmental outcomes for preterm and term infants. This review aims to explain the fundamentals behind aEEG and its clinical applications.