Clinical,Neuroimaging,and Electrographic Predictors of Phenobarbital Failure in Newborns With Hypoxic Ischemic Encephalopathy and Seizures

Abstract

Background:

Many neonates with hypoxic ischemic encephalopathy and seizures do not respond to the first line antiepileptic drug, phenobarbital. Little is known about what factors are associated with its failure.

Objective:

To examine factors associated with failure of phenobarbital therapy in neonates with hypoxic ischemic encephalopathy and seizures.

Design/Methods:

A single-center retrospective review of 50 term (>35 weeks) neonates with hypoxic ischemic encephalopathy and seizures treated with phenobarbital as the first-line antiepileptic. Neonates were classified into either responders (n = 30) or nonresponders (n = 20). Nonresponse was defined as continued seizures after maximum dosing of phenobarbital or an additional antiepileptic. Subjects with acceptable magnetic resonance imaging (MRI) scans obtained within 2 weeks of birth were included in the study and rated using an MRI injury scoring system. Charts were reviewed for demographic, clinical, and laboratory variables. Resuscitation and seizure scores were also calculated. Electroencephalographic (EEG) background activity was reviewed in 2 different time epochs (12-24 hours and 24-36 hours of life) and graded as per ACNS guidelines.

Results:

There were no significant group differences in demographic, clinical, and laboratory variables except nonresponders, who had higher mean seizure score (P = .01) and significantly more injury on MRI scan for white matter (P = .004), parenchymal cortex (P = .027), and watershed (P = .009) regions. Neonates with moderately abnormal or severely abnormal background EEG responded poorly to phenobarbital.

Conclusion:

In the presence of above factors, one can anticipate that additional antiepileptic medication may be needed. These data also support that larger studies should be done to look prospectively at using alternative agents first line in patients with severe injury.

Keywords

neonatal seizures antiepileptic drug hypoxic ischemic encephalopathy neuroimaging electroencephalography

Hypoxic-ischemic encephalopathy, a significant cause of morbidity and mortality in the newborn period, may result in later adverse neurologic outcome. Hypoxic-ischemic encephalopathy affects between 1 and 2 per 1000 live births in developed countries and is estimated to affect between 10 and 20 per 1000 live births in poor or developing countries.¹ Seizures occur frequently in neonates with hypoxic ischemic encephalopathy, with studies reporting an incidence ranging from 30% to 90%.^2
–4 Historically, the first-line anticonvulsant for treatment of seizures in the neonatal intensive care unit is phenobarbital, while second-line medications have included fosphenytoin, midazolam, and recently levetiracetam. Seizures in newborns are difficult to control, and studies performed before the widespread use of therapeutic hypothermia show that traditional first- and second-line antiepileptic drugs are often ineffective.^5,6 Even with hypothermia, electrographic seizures persist (almost 50%) after phenobarbital,^7,8 which may also have adverse neurodevelopmental effects. But little is known about factors associated with phenobarbital failure. Hence, this study was conducted to evaluate the predictors of phenobarbital failure in neonates with hypoxic ischemic encephalopathy and seizures, which may guide further studies to find new treatment regimens for these seizures.

Methods

This was a retrospective single-center cohort study. The Cincinnati Children’s Hospital Institutional Review Board approved the study, including waiver of consent. Neonates treated for hypoxic ischemic encephalopathy between August 2008 and April 2015 were considered for this study. Inclusion criteria for neonates in this study were the following:

Gestational age >35 completed weeks

One of the following: fetal distress at delivery, need for resuscitation at birth, Apgar score <6 at 5 minutes, metabolic acidosis (pH <7.1 or base deficit >10) (These criteria have been used in previously published literature of neonates with perinatal asphyxia or hypoxic ischemic encephalopathy.^9
–11)

Electroencephalographic, electroclinical, or clinical seizures treated according to institutional protocol

Magnetic resonance imaging (MRI) with diffusion-weighted imaging done within first 2 weeks of life

Seizures initially treated with phenobarbital

Exclusion criteria included presence of a known chromosomal anomaly and/or major congenital anomalies, presumed inborn errors of metabolism, genetic epilepsy, severe intrauterine growth restriction (<1800 g birth weight), or gestational age less than 35 weeks. Both cooled and uncooled neonates with hypoxic ischemic encephalopathy and seizures were included in our study. Medical records were comprehensively reviewed and data were collected regarding demographic information, perinatal and neonatal course, and clinical and laboratory findings. A resuscitation score⁹ was calculated: 1 = no intervention; 2 = blow-by oxygen; 3 = endotracheal suctioning; 4 = bag-mask positive pressure ventilation; 5 = endotracheal intubation with positive pressure ventilation; and 6 = endotracheal intubation with ventilation and medication, and the need for chest compressions. A neonatal seizure score⁹ was included: no seizures (score 0); seizures present—seizure frequency (<1 seizure scored as 0, >1 as 1, and status epilepticus as 2); seizure onset day of life (0-1); electroencephalographic (EEG) pattern (0-4).

All neonates were born at an outside facility and then transported to our hospital. All level II and III neonatal units at outside hospitals in our region are staffed by our neonatology group, so standard of care is similar at these outlying hospitals. During the early part of study, there was not a standardized seizure treatment protocol, but phenobarbital was typically the first-line anticonvulsant; there was occasionally some variability in the second-line drug used. Phenobarbital was the first antiseizure medication used in all 50 of the cases in this study per inclusion criteria. None of the neonates received benzodiazepines for seizures prior to phenobarbital administration. Subsequently, a standardized protocol for seizures in newborns was used for management of seizures. This protocol has the following guidelines: (1) loading dose of phenobarbital 20 mg/kg; (2) if seizures continue, second loading dose of phenobarbital 20 mg/kg; (3) if seizures continue, loading dose of levetiracetam 50 mg/kg; (4) if seizures continue, a second loading dose of levetiracetam 50 mg/kg; and (5) if seizures continue, a loading dose of levetiracetam 20 mg/kg. If seizures continue following this loading dose, the attending neonatal neurologist is consulted to determine subsequent medication plan; options include pyridoxine challenge, initiation of midazolam drip, fosphenytoin, or other antiepileptic drugs. Once a loading dose of a given antiepileptic drug is administered, neonates are placed on maintenance dose(s) of the medication(s). The cohort was divided into 2 groups: phenobarbital responders and nonresponders. Nonresponders were defined as those neonates who still had clinical, electroencephalographic, or electroclinical seizures after the maximum dose of phenobarbital and required other antiepileptics to stop seizures. Phenobarbital was typically the first-line anticonvulsant.

Prior to implementation of the standardized seizure protocol, conventional electroencephalography monitoring or amplitude-integrated electroencephalography monitoring was used to detect electroclinical and electroencephalographic seizures in infants with behaviors concerning for seizures. During the initial time period of the study, there was not a standardized monitoring protocol and was at the discretion of the managing pediatric neurologist. After implementation of the protocol, all neonates with hypoxic ischemic encephalopathy were monitored with conventional electroencephalography monitoring (with video monitoring) for at least 24 hours. In subjects with electrographically confirmed seizures, the duration of monitoring varied, but was continued until subjects were seizure free. EEGs were obtained for clinical purposes and were analyzed by board-certified pediatric epileptologists with experience in neonatal EEG and interpretation of maturational changes and any artifact.

MRI was performed using 1.5- and 3-Tesla magnets with sagittal and axial T1, axial fast spin echo proton density and T2, gradient echo, and diffusion-weighted sequences within the first 2 weeks of life (42/50 subjects had the MRI scan performed within 7 days). Images were reviewed for quality. MRI was analyzed by an experienced pediatric neuroradiologist blinded for history of the patients and graded according to hypoxic ischemic encephalopathy MRI Injury Grading Score,¹² which included brainstem, cerebellar, white matter, parenchymal (cortex), hippocampal, parenchymal hemorrhage, basal ganglia/thalamus, posterior limb of internal capsule, intraventricular hemorrhage (this is not listed in table), watershed and ventriculomegaly regions (not included in table) of brain. This MRI scoring system included and expanded upon others shown to be predictive of neurodevelopmental outcome.^12
–14

EEG background analysis was done in 2 time epochs, 12 to 24 hours of life and 24 to 36 hours of life, by an experienced pediatric epileptologist blinded for the clinical and treatment history of the neonate and who analyzed actual EEG recordings of the neonate. Because it is a retrospective study, not all neonates had EEG during these time epochs, so records of only 23/50 neonate were available for first epoch and 29/50 neonate for second epoch. Both epochs were separately analyzed for both groups as nonresponders versus responders. The EEG background activity was graded into 4 groups according to previously defined criteria with some adaptation^15,16 and to the new ACNS guidelines¹⁷: normal/mildly abnormal (continuous background activity with slightly abnormal activity, eg, mild asymmetries, mild voltage depression, poorly defined sleep-wake cycling), moderately abnormal (discontinuous activity with interburst interval ≤10 seconds, no clear sleep-wake cycling, clear asymmetry, or asynchrony), severely abnormal (discontinuous activity with interburst interval 10-60 seconds, severe attenuation of background activity, no sleep-wake cycles), and isoelectric EEG (background activity <5 µV or severe discontinuity with interburst interval >60 seconds).

Statistical Analysis

Response to phenobarbital was the primary independent variable. Data were analyzed using SPSS, version 20, software. Categorical variables were reported as percentages and compared using chi-square and Fisher exact test; continuous variables were reported as means with standard errors of mean using Student t test. Two-sided P value <.05 was considered as statistically significant. A receiver operating characteristic curve was calculated for the various variables used in the study for prediction of nonresponse, and the area under the curve was calculated. We further calculated cut-off values for these scores, above which there is very high chance of nonresponse, and rounded them to the nearest absolute value.

Results

One hundred twenty-seven neonates with hypoxic ischemic encephalopathy were identified from medical records. Appropriate MRI data were not available in 58 neonates, and another 19 neonates did not have seizures. Thus, 50 neonates met the inclusion criteria for the study: 30 neonates who were responders and 20 who were nonresponders and had similar baseline demographic and clinical data (Table 1). There was a nonsignificant increase in the percentage of neonates cooled in the responder group (20/30 or 67%) compared to the nonresponder group (8/20 or 40%) (P = .09).

Table 1.

Base Line Characteristics of the Study Cohort (n=50).^a

Characteristics	Responders(n=30)	Nonresponders (n=20)	P value
Infant characteristics
Male	15 (50)	13 (65)	.39
Gestational age, wk (mean ± SEM)	37.7 (1.3)	38.7 (0.4)	.59
Birth weight, g (mean ± SEM)	3339 (135)	3105 (155)	.26
Head circumference, cm (mean ± SEM)	34.2 (0.39)	34.1 (0.46)	.84
Caesarean section	18 (60)	11 (55)	.86
Apgar score, 1 min (mean ± SEM) Apgar score, 5 min (mean ± SEM)	1.8 (0.4) 3.5 (0.6)	3.2 (0.6) 5.2 (0.8)	.08 .09
Cord pH (mean ± SEM)	6.9 (0.9)	7.00 (0.00)	.32
Positive pressure ventilation	27 (90)	17 (85)	.67
Intubation	24 (80)	15 (75)	.74
Chest compression	14 (46.6)	5 (25)	.11
Epinephrine	8 (26.6)	5 (25)	1.00
Resuscitation score (mean ± SEM)	5.0 (0.3)	4.2 (0.4)	.65
Seizure score (mean ± SEM)	3.1 (0.4)	4.8 (0.5)	.01
Total phenobarbital dose (mean ± SEM) (mg/kg)	28.7 (2.1)	38.0 (1.9)	.04
Hypothermia	20 (66.7)	8 (40)	.09
Maternal characteristics
Maternal age, y (mean ± SEM)	27.6 (1.1)	24.9 (1.2)	.13
First child	12 (40)	11 (55)	.24
Hypertension	7 (23.3)	8 (40)	.17
Gestational diabetes	5 (16.7)	1 (5)	.38
Fetal distress	16 (53.3)	12 (60)	.77

Abbreviation: SEM, standard error of the mean.

^aValues are n (%) unless otherwise noted.

Total Cohort

In the nonresponder group, the mean neonatal seizure score (4.8 ± 0.5) and mean phenobarbital dose (38.0 ± 1.9 mg/kg) were higher than in the responder group (seizure score 3.1 ± 0.4, P = .01; mean phenobarbital dose 28.7 + 2.1 mg/kg, P = .004). A receiver operating characteristic curve was made for the seizure score, which showed an area under the curve value of 0.763 (95% CI 0.621-0.905), and the cut-off value for seizure score was found to be ≥6 (for having a poor response (Figure 1, Table 4). When MRI injury grading scores were analyzed, there was a significantly higher percentage of nonresponders to phenobarbital, who had more severe grading for the white matter (P = .004), parenchymal cortical (P = .03), and watershed regions in the brain (P = .009) (Table 2). Receiver operating characteristic curve for MRI injury grading score showed that the watershed lesion (0.747 95% CI 0.605-0.890) had the highest area under the curve for prediction of nonresponse to phenobarbital (Table 4, Figure 1) compared with other MRI measures.

Table 2.

Hypoxic Ischemic Encephalopathy Magnetic Resonance Imaging (MRI) Injury Grading Score in Neonates With Hypoxic Ischemic Encephalopathy and Seizures.

Region of brain (score)	Responders, n (%)(n = 30)	Nonresponders, n (%)(n = 20)	P value
Brainstem
0. None	24 (80)	14 (70)	.66
1. Focal	1 (3.3)	2 (10)
2. Diffuse	5 (16.7)	4 (20)
Cerebellar
0. None	26 (86.7)	17 (85)	1.00
1. <3 punctuate lesion (<2 mm)	1 (3.3)	0 (0)
2. >3 punctuate lesion (<2 mm) or confluent large areas	3 (10)	3 (15)
White matter
0. Normal	14 (46.7)	1 (5)	.004
1. Minimal (≤3 lesions)	1 (3.3)	1 (5)
2. Moderate(≥3 lesions or bilateral)	2 (6.7)	2 (10)
3. Severe (multiregional lesion/watershed)	13 (43.3)	16 (80)
Parenchymal—cortical
0. Normal	20 (66.7)	5 (25)	.03
1. Single focal infarction	0 (0)	0 (0)
2. Abnormal cortex and white matter anterior or posterior	2 (6.7)	1 (5)
3. Abnormal signal in both anterior and posterior watershed zone	4 (13.3)	7 (35)
4. Extensive cortical injury	4 (13.3)	7 (35)
Hippocampal
0. None	22 (73.3)	12 (60)	.10
1. Unilateral	0 (0)	3 (15)
2. Bilateral	8 (26.7)	5 (25)
Parenchymal hemorrhage—not grade 4
0. Negative	22 (73.3)	18 (90)	.18
1. Positive microhemorrhage	6 (20)	1 (5)
2. Positive hemorrhage >2 mm	2 (6.7)	1 (5)
Parenchymal—basal ganglia/thalamus injury
0. Normal	12 (40)	4 (20)	.58
1. Abnormal signal thalamus	1 (3.3)	2 (10)
2. Abnormal signal thalamus and lentiform nucleus	5 (16.7)	5 (25)
3. Abnormal signal thalamus lentiform nucleus and perirolandic cortex	7 (23.3)	6 (30)
4. Extensive	5 (16.7)	3 (15)
Posterior limb of the internal capsule
0. Myelination present	15 (50)	8 (40)	.66
1. Impaired myelination	3 (10)	1 (5)
2. Myelination absent with reversed or abnormal signal on T1 or T2	12 (40)	11 (55)
Watershed region
0. Normal	18 (60)	3 (15)	.009
1. Single focal infarction	0	0
2. Abnormal signal in anterior or posterior watershed cortex and white matter	2 (6.7)	2 (10)
3. Abnormal signal in both anterior and posterior watershed cortex and white matter	3 (10)	1 (5)
4. Abnormal signal in both anterior and posterior watershed zones	3 (10)	8 (40)
5. More extensive cortical involvement	4 (13.3)	6 (30)

Table 3.

EEG Findings in Neonates With Hypoxic Ischemic Encephalopathy and Seizures.

EEG background	12-24 h (n = 23)			24-36 h (n = 29)
EEG background	Responders, n (%)	Nonresponders, n (%)	P value	Responders, n (%)	Nonresponders, n (%)	P value
Normal/mildly abnormal	6 (42.9)	2 (22.2)	.017	6 (42.9)	6 (40)	.018
Moderately abnormal	1 (7.1)	3 (33.3)		0 (0)	5 (33.3)
Severely abnormal	1 (7.1)	4 (44.4)		3 (21.4)	4 (26.7)
Isoelectric	6 (42.9)	0 (0)		5 (35.7)	0 (0)
Total	14	9		14	15

Abbreviation: EEG, electroencephalographic.

Table 4.

AUC and Cut-Off Values for Significant Variables Associated With Nonresponse.

Variable(s)	AUC	SE	P value	95% CI		Cut-off values of score
Seizure score	0.754	0.073	.003	0.611	0.898	≥5
MRI injury grading score
White matter	0.725	0.072	.008	0.584	0.867	≥2
Watershed	0.747	0.073	.004	0.605	0.890	≥3
Parenchymal	0.714	0.077	.012	0.563	0.865	≥3

Abbreviations: AUC, area under the curve; MRI, magnetic resonance imaging; SE, standard error.

EEG background analysis at 12 to 24 hours of life showed that moderately abnormal (responder vs nonresponder: 7.1% vs 33.3%) and severely abnormal background activity (responder vs nonresponder: 7.1% vs 44.4%) were significantly associated with nonresponse to phenobarbital (Table 3). Similar results were also there in 24 to 36 hours of life. Neonates having isoelectric EEG did not require another antiepileptic medication other than phenobarbital to control their seizures in both time epochs.

Thirty-four neonates received phenobarbital before EEG whereas 13 neonates did not (data not available for 3 neonates). There was no significant difference between these 2 groups for MRI injury grading scores or EEG background analysis at 12 to 24 hours and 24 to 36 hours of life.

Electrically Confirmed Seizures Subgroup

Electrographically confirmed seizures were detected in 10 responder and 15 nonresponder neonates. In the nonresponder group, the mean neonatal seizure score (5.6 ± 0.5) was higher than in the responder group (seizure score 4.9 ± 0.4, P = .31).

When MRI injury grading scores were analyzed in those neonates with electrographically confirmed seizures, there was a significantly higher percentage of nonresponders to phenobarbital who had more severe grading for white matter (P = .036).

EEG background analysis at 12 to 24 hours of life showed that moderately abnormal (responder vs nonresponder: 11% vs 43%) and severely abnormal background activity (responder vs nonresponder: 11% vs 29%) were significantly associated with nonresponse to phenobarbital. Similar results were also found for 24 to 36 hours of life, moderately abnormal (responder vs nonresponder: 0% vs 25%), and severely abnormal background activity (responder vs nonresponder: 17% vs 25%), though it did not reach significance. Neonates having isoelectric EEG did not require another antiepileptic medication other than phenobarbital to control their seizures in both time epochs.

Discussion

Phenobarbital is used as the first-line anticonvulsant in most neonatal intensive care units all over the world. But often it is not effective in many cases of birth asphyxia.¹⁸ It is speculated that persistence of subclinical seizures due to failure of phenobarbital may contribute to the adverse neurodevelopment in these neonates. Our study examines factors associated with phenobarbital failure in neonates with hypoxic ischemic encephalopathy and seizures. In our study cohort of 50 neonates, phenobarbital resistance was seen in 40%, which is slightly higher than previous studies.¹⁹ This discrepancy may be related to differences in patient populations; whereas our study only included neonates with seizures from birth asphyxia, other studies includes all neonates with seizures of various etiologies.

Demographic and clinical factors that might be predictive of phenobarbital failure were similar in both groups. Seizure score in these neonates, however, was associated with phenobarbital response. Patients with higher seizure score had greater chance of nonresponse. Our study is the first to statistically show severity of seizures in newborns as a predictor of phenobarbital nonresponse. Similar to previous studies showing a decreased seizure burden in neonates with hypoxic ischemic encephalopathy treated with hypothermia,^20
–22 our study showed that neonates treated with hypothermia responded better to phenobarbital, though this did not reach statistical significance. Hypothermia may prevent secondary energy failure, which is the cause for seizures, thereby lessening the seizure burden.

A significant finding in our study was that the severity of brain injury measured with MRI scan was associated with nonresponse to phenobarbital, in agreement with a previous study.² We were able to calculate a cut-off score with good sensitivity and specificity for prediction of response. Additionally, our study is the first to show that a specific pattern of injury predicts response to phenobarbital, with injury to white matter, parenchymal cortical, and watershed more severe in nonresponders compared with responders. The watershed injury (which may include both white matter and the parenchymal cortex) was calculated to have the best sensitivity and specificity with the receiver operating curve. It may be concluded that cortical injury as opposed to basal ganglia injury may be a better predictor of phenobarbital response.

Another finding of our study was that moderately and severely abnormal EEG background was associated with nonresponse to phenobarbital. Thus, EEG background may be a surrogate marker of severe injury in the brain and thus can predict poor response to phenobarbital, as was also shown in a previous study.²³ Because an EEG can be obtained at presentation, this can allow for early prediction of phenobarbital response, as opposed to MRI scan which is not obtained until later. In our study, it was surprising to find that neonates with an isoelectric interictal EEG pattern seemed to have responded to phenobarbital. It may be that these neonates are not capable of generating prolonged seizures and although they have poor prognosis, their seizures may be easy to treat.

Our study had the following limitations: (1) Because of the retrospective design, there was variability in documentation and available clinical data; subjects were not treated or monitored in a standardized protocol; and techniques for cooling evolved over time, so this was not controlled for. (2) There was nonavailability of data for background EEG analysis for some neonates, so sample size was small for this analysis. (3) There was a lack of a standardized EEG monitoring protocol during the earlier part of our study, so seizure burden could not be assessed. (4) There was a lack of EEG confirmation of seizures, so not all treatment responses may have been true responders and it is possible that electroencephalographic seizures were missed in our responder group because of this. However, phenobarbital levels were lower in the responder group, making it less likely that electroclinical dissociation was more common in the responder group. Further, when only subjects with electrographically confirmed seizures were studied, similar results were observed.

Despite these limitations, our study shows that nonresponse to phenobarbital is associated with a higher seizure score, specific MRI injury patterns, and severe patterns in EEG background. In the presence of such lesions, a higher seizure score or a severely abnormal EEG, one can anticipate that additional antiepileptic medication may be needed. These data also support that larger studies should be done to look prospectively at using alternative agents first line in patients with severe injury.

Footnotes

Acknowledgments

The authors thank the Nurturing Children Development Program of the Global Health Center, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, for the scholarship under which this study was conducted.

Author Contributions

DD and MS conceived and planned the study, and supervised the conduct of the study and preparation of the manuscript. DD, CV, and MS enrolled subjects, collected clinical data, analyzed data, and prepared the initial draft of the manuscript. BKF supervised the radiologic assessment of MRI images and graded them. NL and KH graded EEG background activity and helped in the preparation of the manuscript. All authors approved the final manuscript for publication.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Ethical Approval

This study was approved by the Institutional Review Board at Cincinnati Children’s Hospital Medical Center. (IRB approval number: 2013-7409).

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