Behavioral changes correlated with brain-stem auditory evoked responses in term infants with moderate hyperbilirubinemia

Neonatal hyperbilirubinemia and repercussions on neurodevelopment: A systematic review

BACKGROUND

Accumulation of bilirubin above normal levels is considered a neurological risk factor for both premature and full-term newborns. This systematic review aimed to determine the effect of neonatal hyperbilirubinemia on neurodevelopment in preterm and full-term newborns.

METHODS

PubMed, EMBASE, Cochrane Library, CINAHL, PsycINFO, Scopus and Lilacs databases were searched for articles published until 1 June 2022. The quality of cohort and case-control studies was assessed with the Newcastle-Ottawa Scale, and the MINCir scale was used to evaluate the methodological quality of therapy studies or the therapeutic procedures. Premature neonates without neurological conditions and those born at term with hyperbilirubinemia as the sole risk factor were included. Studies reporting one or more neurodevelopmental outcomes were included with an inter-group comparison of a hyperbilirubinemia group versus a non-hyperbilirubinemia or non-pathological hyperbilirubinemia group. The main outcomes were auditory function, visual function, cognitive function, motor function, behavior, global development and neurological risk.

RESULTS

The search identified 951 studies, 19 of which (n = 2210 newborns) were finally included. Fifteen of the cohort and case-control studies presented low risk of bias, and six studies showed high methodological quality. Within the preterm population, hyperbilirubinemia as the sole risk factor was not shown to affect neurodevelopment. Auditory, neurological and motor development alterations were found in the population of full-term newborns with hyperbilirubinemia, which were more evident during the first year of life.

CONCLUSIONS

Elevated bilirubin levels may be a trigger for the onset of neurodevelopmental disorders in full-term infants during the first year of life. More studies are warranted in the preterm population with hyperbilirubinemia to draw conclusions about its impact on their neurodevelopment.

Long-term Effects of Indirect Hyperbilirubinemia on Auditory and Neurological Functions in Term Newborns

Objective:

The aim of this study was to investigate the long-term effects of hyperbilirubinemia on neurological and hearing function in otherwise healthy term newborns with neonatal indirect hyperbilirubinemia.

Method:

This study was performed prospectively in 41 term newborns hospitalized for indirect hyperbilirubinemia. Patients with no signs of hemolysis were categorized in 3 groups based on stabil levels as sTB <20 mg/dl, 20-24.9 mg/dl, and =>25 mg/dl. Patients with total bilirubin level =>20 mg/dl and hemolytic disease were classified as the fourth group. The relationship between maximum sTB level, duration of exposure to sTB levels >20 mg/dl and etiology of jaundice with neurological and auditory functions was investigated. Detailed neurological examination, Denver II developmental screening test and hearing tests (otoacoustic emissions, OAE and auditory brainstem responses, ABR) were performed to all patients between 18-24 months of age.

Results:

Neurodevelopmental disorder was found in 5 (12.2%) patients. Hemolytic disease was detected in two of these patients. Hearing loss was found in 4 (9.8%) of the patients. Two of these patients had auditory neuropathy spectrum disorder and the other two had cochlear hearing loss. The sTB levels of all these patients were above 25 mg/dl. No neurological disorder or hearing loss was found in the patients who had stabil of <25 mg/dl. Exposure time to sTB levels above 20 mg/dl was significantly longer in patients with neurological dysfunction and pathologic ABR results (p:0.007, p:0.007; p<0.05).

Conclusion:

This study demonstrates that kernicterus may develop in term newborns with severe hyperbilirubinemia (sTB>25 mg/dl) without any finding of significant hemolysis. Not only the bilirubin level but also the duration of exposure to high bilirubin levels may be effective in the development of bilirubin neurotoxicity. The high rate of hearing loss in our patients emphasizes the importance of screening for infants with severe hyperbilirubinemia using comprehensive auditory evaluation for early diagnosis of possible hearing loss.

The clinical syndrome of bilirubin-induced neurologic dysfunction

Clinicians have hypothesized a spectrum of minor neurologic manifestations, consistent with neuroanatomical reports and collectively termed as a "syndrome of bilirubin-induced neurologic dysfunction (BIND)," which can occur in the absence of classical kernicterus. The current review builds on these initial reports with a focus on clinical signs and symptoms that are assessed by standardized tools and manifest from neonatal age to childhood. These clinical manifestations are characterized by the following domains: (i) neuromotor signs; (ii) muscle tone abnormalities; (iii) hyperexcitable neonatal reflexes; (iv) variety of neurobehavior manifestations; (v) speech and language abnormalities; and (vi) evolving array of central processing abnormalities, such as sensorineural audiology and visuomotor dysfunctions. Concerns remain that the most vulnerable infants are likely to acquire BIND, either because their exposure to bilirubin is not identified as severe enough to need treatment or is prolonged but slightly below current threshold levels for intervention. Knowing that a total serum/plasma bilirubin (TB) level is not the most precise indicator of neurotoxicity, the role of expanded biomarkers or a "bilirubin panel" has yet to be validated in prospective studies. Future studies that correlate early "toxic" bilirubin exposure to long-term academic potential of children are needed to explore new insights into bilirubin's effect on the structural and functional maturation of an infant's neural network topology.

Visuocortical bilirubin-induced neurological dysfunction

This review addresses the question whether elevated levels of total serum/plasma bilirubin (TB) cause measurable neurological effects, specifically to visuocortical functioning. Past research in the area of vision and its relation to jaundice has taken advantage of flash visual-evoked potentials (VEPs). Using a steady state VEP, we developed preliminary data suggesting that children who had jaundice with TB levels between 10 and 25mg/dL, but who did not have kernicterus, have measurable changes in visual function, when compared to control infants who did not have jaundice. This non-invasive test offers information about vision thresholds, signal amplitudes, and suprathreshold changes after brain exposure to bilirubin. Here, we review this novel tool, the steady state VEP, and data suggesting that neurological changes occur in infants with moderately elevated TB levels.

Neurobehavior of term neonates with neonatal hyperbilirubinemia

Objective:

To find the effect of neonatal hyperbilirubinemia on neurobehavior of term infants.

Materials and Methods:

This study was undertaken in the neonatal unit of our tertiary care hospital. Term neonates who developed jaundice with serum bilirubin value of above 15 mg/dl within 1^st week of life were enrolled in the study. Peak total serum bilirubin (PSB) levels of cases were recorded. Age and sex matched normal controls were assigned to every case. Both the groups were assessed by Brazelton′s neurobehavioral assessment scale (NBAS) and the scores of the individual clusters were compared.

Results:

Habituation, range of state, autonomic regulation and regulation of state clusters were significantly altered in the case group, while motor organization cluster was mainly affected in neonates with severe jaundice (PSB > 25 mg/dl). No differences were noted in the reflex and orientation NBAS clusters.

Conclusion:

Neonatal hyperbilirubinemia causes definite alteration in the neonatal neurobehavior.

Hypotonia, jaundice, and Chiari malformations: relationships to executive functions

This article postulates that movement and action control are the underpinning of executive functioning. We selectively examine brain regions that have traditionally been almost exclusively understood as critical to the control and expression of movement-namely, the basal ganglia and the cerebellum. We first describe the relationship between movement and cognition. This is followed by a review of common developmental disorders that are known to exhibit abnormal executive functions and movement anomalies. Against that background, we examine hypotonia, neonatal jaundice, and Chiari I malformation, and we demonstrate why these are "at-risk" factors for neurodevelopmental disorders that can feature both motor control and executive function abnormalities. Our goal is to prepare the clinical neuropsychologist for gathering information about these features of a child's birth and developmental histories, while using this as a framework for interpreting test results and applying test data in a useful, practical way to guide descriptive diagnosis and treatment.

Hyperbilirubinemia: subcortical mechanisms of cognitive and behavioral dysfunction

Although development of the full syndrome of kernicterus is relatively rare, neonatal jaundice continues to occur frequently. Controversy remains concerning whether or not infants with moderate elevations in bilirubin are at risk for neurodevelopmental disorders in later childhood. Sites of brain pathology associated with bilirubin neurotoxicity are identified and well established. Based on these regions of brain involvement, we apply neuroscientific principles of brain-behavior relationships to predict types of cognitive features that may accompany hyperbilirubinemia. We address a range of neurodevelopmental abnormalities that can arise as a function of elevated neonatal bilirubin levels affecting these brain regions, even in the absence of full kernicterus syndrome. Moreover, we explain the neuropathologic mechanisms that would drive these abnormalities. We thus attempt to establish a blueprint for future investigations of these conditions, to improve neurodevelopmental outcomes.

The clinical syndrome of bilirubin-induced neurologic dysfunction

We believe that the syndrome of bilirubin-induced neurologic dysfunction [BIND] represents a spectrum of neurologic manifestations among vulnerable infants who have experienced an exposure to bilirubin of lesser degree than generally described in previous publications. Clinical neuro-motor manifestations extend to a range of subtle processing disorders with objective disturbances of visual-motor, auditory, speech, cognition, and language among infants with a previous history of moderate-to-severe hyperbilirubinemia of varied duration. Confounding effects include prematurity, hemolysis, perinatal-neonatal complications, altered bilirubin-albumin binding, severity and duration of bilirubin exposure, and the individual vulnerability of the infant related to genetic, family, social, and educational predilection, regardless of the cause of neonatal jaundice. Tools to better assess BIND specific domains of multisensory processing disorders, identified by pyschometric, audiologic, speech, language and visual-motor, and neuromotor examination would allow for prospective surveillance of infants at risk for the syndrome.

Kernicterus in preterm infants

OBJECTIVE

We sought to clarify the features of kernicterus in preterm infants.

METHODS

The subjects of this study were 8 preterm infants with athetoid cerebral palsy whose gestational ages were < or =34 weeks. We retrospectively investigated clinical, laboratory, MRI, and brainstem auditory evoked potential (BAEP) findings.

RESULTS

Gestational age was < or =26 weeks in 6 of the 8 infants, and birth weight was <1000 g in 5 infants. Serious postnatal complications with systemic deterioration were observed in 3 infants. Total bilirubin levels were measured frequently in the majority of infants; peak values of >15 mg/dL were observed in 3 infants. No infant showed neurologic symptoms characteristic of classical acute bilirubin encephalopathy during the neonatal period. Dystonic posture and abnormal muscle tone were first recognized within 6 months' corrected age in all patients. During infancy, MRI was performed in 7 infants. Abnormal high-intensity areas were observed in the bilateral globi pallidi in all 7 infants. However, MRI during the neonatal period or after 1 year's corrected age showed no abnormal findings. BAEP measurements were abnormal in 7 of the 8 infants.

CONCLUSIONS

Preterm infants with athetotic cerebral palsy showed rather homogeneous features, similar to term infants with kernicterus, with marked hyperbilirubinemia. This combination of clinical, laboratory, neuroimaging, and neurophysiological data will contribute to the increased recognition of preterm infants with kernicterus.

Pedaudiologic findings after severe neonatal hyperbilirubinemia

Neonatal hyperbilirubinemia (NHB) above 20 mg/dl (NHB20) has been shown to increase the risk of hearing impairments. Up to now, audiological findings based on behavioural audiometry (BA), otoacoustic emissions (TEOAE) and auditory brainstem responses (ABR) from children after being diagnosed with NHB20 have not been thoroughly compared to those with lower NHB-levels. We, therefore, aimed to assess the presence and characteristics of auditory dysfunction in children with NHB20. The audiological data of 15 children aged 11 months to 9 years with a NHB level between 22.6 and 45.6 mg/dl and/or MRI-confirmed bilirubin encephalopathy (NHBG) were compared retrospectively to 15 children with NHB levels between 12.5 and 19.4 mg/dl (CG). After matching by weeks of gestation at birth, BA, TEOAE and ABR were performed in all the children. Subsequently the groups were compared. Only two children of the NHBG had consistently normal audiologic findings. Hearing function disorders were detected in 87% (13/15) of the NHBG-children, ranging from total deafness to normal BA, including unilateral and bilateral deafness as well as cochlear hearing loss. Auditory neuropathy/dys-synchrony (AN) was found in a total of eight children (53%) of the NHBG. In addition, it was found that after the occurrence of NHB20, initially detected TEOAE can disappear in some cases. In the comparison group (CG) only two children demonstrated a hearing dysfunction, both of which were cochlear hearing impairments, whereas no child had AN. A bias towards hearing impairments has to be taken into account for both groups. Detailed pedaudiologic testing should be mandatory for all children after the occurrence of NHB20 including follow-up during the first 12 months. Audiological diagnostic work-up in the affected children requires objective investigations of hearing functions, while BA is recommended to evaluate the adequate therapeutic procedure.

Effects of antenatal magnesium sulfate and corticosteroid therapy on sleep states of preterm infants

This exploratory longitudinal study was designed to compare the neonatal illness severity, sleep-wake, and respiratory sleep behaviors of preterm infants whose mothers received prenatal corticosteroids and/or magnesium sulfate (MgSO4) with those of infants whose mothers did not receive these medications. The 134 infants were divided into four groups: those whose mothers received MgSO4 only, those who received steroids only, those who received both MgSO4 and steroids, and those who received neither. The groups did not differ on infant characteristics or illness severity. Infants exposed to MgSO4 had more active sleep without rapid eye movement, indicating poorly organized active sleep. The MgSO4 -only group had higher quiet sleep regularity scores and fewer state changes. These findings suggest that fetal exposure to MgSO4 may subtly affect the central nervous system.

Toward understanding kernicterus: a challenge to improve the management of jaundiced newborns

PURPOSE

We sought to evaluate the sensitivity and specificity of total serum bilirubin concentration (TSB) and free (unbound) bilirubin concentration (Bf) as predictors of risk for bilirubin toxicity and kernicterus and to examine consistency between these findings and proposed mechanisms of bilirubin transport and brain uptake.

METHODS

A review of literature was undertaken to define basic principles of bilirubin transport and brain uptake leading to neurotoxicity. We then reviewed experimental and clinical evidence that relate TSB or Bf to risk for bilirubin toxicity and kernicterus.

RESULTS

There are insufficient published data to precisely define sensitivity and specificity of either TSB or Bf in determining risk for acute bilirubin neurotoxicity or chronic sequelae (kernicterus). However, available laboratory and clinical evidence indicate that Bf is better than TSB in discriminating risk for bilirubin toxicity in patients with severe hyperbilirubinemia. These findings are consistent with basic pharmacokinetic principles involved in bilirubin transport and tissue uptake.

CONCLUSIONS

Experimental and clinical data strongly suggest that measurement of Bf in newborns with hyperbilirubinemia will improve risk assessment for neurotoxicity, which emphasizes the need for additional clinical evaluation relating Bf and TSB to acute bilirubin toxicity and long-term outcome. We speculate that establishing risk thresholds for neurotoxicity by using newer methods for measuring Bf in minimally diluted serum samples will improve the sensitivity and specificity of serum indicators for treating hyperbilirubinemia, thus reducing unnecessary aggressive intervention and associated cost and morbidity.

Neurological complications of kernicterus

OBJECTIVE AND BACKGROUND

Prevention of bilirubin encephalopathy relies on the detection of newborns who are at risk of developing serious hyperbilirubinemia. The objective of this study was to reassess the clinical syndrome of kernicterus as neurodiagnostic studies have become more readily available and can be used to evaluate these infants.

METHODS

The study population was neonates born at term or near term admitted to The Hospital for Sick Children in Toronto, Ontario, Canada, between January 1990 and May 2000. During the study period, there were 9776 admissions (average number of admissions per year--888 infants). The inclusion criteria were that patients had total serum bilirubin levels of >400 micromol/L at the time of diagnosis and no evidence of hypoxic ischemic encephalopathy. Records were reviewed to establish neurodevelopment outcomes.

RESULTS

Twelve neonates (nine males) were identified. Bilirubin levels at the time of diagnosis ranged from 405 to 825 micromol/L. Causes of these elevated levels included glucose-6-phosphate dehydrogenase deficiency (seven patients), dehydration (three patients), sepsis (one patient), and was undetermined in one patient. Abnormal visual evoked potentials were found in three of nine patients and abnormal brainstem auditory evoked potentials in seven of ten patients. Abnormal electroencephalograms were documented in five patients studied. Brain magnetic resonance imaging results were abnormal in three of four patients.

CONCLUSIONS

Magnetic resonance imaging typically showed an increased signal in the posteromedial aspect of the globus pallidus and was, therefore, useful in the assessment of the structural changes of chronic bilirubin encephalopathy after kernicterus.

Auditory brainstem response detects early bilirubin neurotoxicity at low indirect bilirubin values

When sedation, prematurity or other disease processes mask symptoms in the clinically ill newborn, serum bilirubin concentration is monitored as the sole indicator of kernicterus risk. This case emphasizes the value of auditory brainstem responses for the management of indirect hyperbilirubinemia complicated by prematurity, hemolytic anemia, asphyxia, and direct hyperbilirubinemia.

An evidence-based review of important issues concerning neonatal hyperbilirubinemia

This article is adapted from a published evidence report concerning neonatal hyperbilirubinemia with an added section on the risk of blood exchange transfusion (BET). Based on a summary of multiple case reports that spanned more than 30 years, we conclude that kernicterus, although infrequent, has at least 10% mortality and at least 70% long-term morbidity. It is evident that the preponderance of kernicterus cases occurred in infants with a bilirubin level higher than 20 mg/dL. Given the diversity of conclusions on the relationship between peak bilirubin levels and behavioral and neurodevelopmental outcomes, it is apparent that the use of a single total serum bilirubin level to predict long-term outcomes is inadequate and will lead to conflicting results. Evidence for efficacy of treatments for neonatal hyperbilirubinemia was limited. Overall, the 4 qualifying studies showed that phototherapy had an absolute risk-reduction rate of 10% to 17% for prevention of serum bilirubin levels higher than 20 mg/dL in healthy infants with jaundice. There is no evidence to suggest that phototherapy for neonatal hyperbilirubinemia has any long-term adverse neurodevelopmental effects. Transcutaneous measurements of bilirubin have a linear correlation to total serum bilirubin and may be useful as screening devices to detect clinically significant jaundice and decrease the need for serum bilirubin determinations. Based on our review of the risks associated with BETs from 15 studies consisting mainly of infants born before 1970, we conclude that the mortality within 6 hours of BET ranged from 3 per 1000 to 4 per 1000 exchanged infants who were term and without serious hemolytic diseases. Regardless of the definitions and rates of BET-associated morbidity and the various pre-exchange clinical states of the exchanged infants, in many cases the morbidity was minor (eg, postexchange anemia). Based on the results from the most recent study to report BET morbidity, the overall risk of permanent sequelae in 25 sick infants who survived BET was from 5% to 10%.

Long-term outcome of neonatal hyperbilirubinaemia: subjective and objective audiological measures

Neonatal hyperbilirubinaemia is a common cause of early onset sensorineural hearing loss. There is no exact method to detect the extent of the neurotoxicity of bilirubin. On the other hand, the auditory pathway is known to be one of the most sensitive parts of the central nervous system (CNS) to this toxic agent. This prospective follow-up study was performed to evaluate and compare the factors related to the hearing of neonates with severe hyperbilirubinaemia and an age-matched control group. Both of these groups were tested using auditory brainstem response (ABR) as well as evoked otoacoustic emissions. Additionally, both of these groups of children were evaluated subjectively using an early speech-language-communication evaluation questionnaire. There was no significant difference in either objective (ABR and evoked otoacoustic emission) or subjective assessment (questionnaire) between the study and control groups. Furthermore, no correlation between serum total bilirubin levels and ABR latencies or thresholds was found within the study group.

New concepts in bilirubin encephalopathy

Revised concepts of bilirubin encephalopathy have been revealed by studies of bilirubin toxicity in cultured CNS cells and in congenitally jaundiced Gunn rats. Bilirubin neurotoxicity is related to the unbound (free) fraction of unconjugated bilirubin (Bf), of which the dominant species at physiological pH is the protonated diacid, which can passively diffuse across cell membranes. As the binding affinity of plasma albumin for bilirubin decreases strikingly as albumin concentration increases, previously reported Bf values were underestimated. Newer diagnostic tests can detect reversible neurotoxicity before permanent damage occurs from precipitation of bilirubin (kernicterus). Early toxicity can occur at Bf only modestly above aqueous saturation and affects astrocytes and neurons, causing mitochondrial damage, resulting in impaired energy metabolism and apoptosis, plus cell-membrane perturbation, which causes enzyme leakage and hampers transport of neurotransmitters. The concentrations of unbound bilirubin in the cerebro-spinal fluid and CNS cells are probably limited mainly by active export of bilirubin back into plasma, mediated by ABC transporters present in the brain capillary endothelium and choroid plexus epithelium. Intracellular bilirubin levels may be diminished also by oxidation, conjugation and binding to cytosolic proteins. These new concepts may explain the varied susceptibility of neonates to develop encephalopathy at any given plasma bilirubin level and the selective distribution of CNS lesions in bilirubin encephalopathy. They also can suggest better strategies for predicting, preventing and treating this syndrome.

Moderate hyperbilirubinemia induces a transient alteration of neonatal behavior

OBJECTIVE

To investigate the behavioral changes induced by moderate hyperbilirubinemia in the otherwise healthy, untreated newborn infant.

METHODS

Fifty term neonates (23 boys) with untreated moderate hyperbilirubinemia (median: 14.3 mg/dL; range: 13.2-20 mg/dL) and 50 matched control subjects with lower bilirubin concentrations (median: 9.1 mg/dL; range: 5.3-12 mg/dL) were administered the Brazelton Neonatal Behavioral Scale at 87 hours of life (range: 72-110 hours). A subgroup analysis was also performed at 104 hours of life (range: 96-134 hours) and at 3 weeks of age.

RESULTS

At the first examination, all behavioral clusters were significantly altered in the group with moderate hyperbilirubinemia. The visual and auditory capabilities of the hyperbilirubinemic infant were especially compromised. Although social-interactive cluster scores significantly correlated both with serum bilirubinemia and birth weight, the former accounted for 8.7% of the variance and the latter accounted for only 4.7%. The moderate hyperbilirubinemia neonates' scores also showed a negative correlation with the autonomic system and more frequent presence of tremors. After 24 hours, a decrease in serum bilirubin within the moderate hyperbilirubinemic group was associated with improved scores. At 3 weeks of age, the behavioral assessment of the 2 groups did not show significant differences.

CONCLUSIONS

Untreated moderate hyperbilirubinemia is associated with a transient and apparently reversible alteration of neonatal behavior, particularly in the social-interactive area.

Is auditory brainstem response a bilirubin neurotoxicity marker?

PURPOSE

To find a correlation between increasing levels of serum bilirubin and auditory brainstem responses (ABR) and to find the use of ABR as a bilirubin neurotoxicity marker.

MATERIAL AND METHODS

A prospective study of 60 neonates in which ABR of hyperbilirubinemic neonates was compared with the normal neonates. All cases with abnormal ABR were studied for 6 months and after 1 month and 6 months a repeat ABR was performed.

RESULTS

Brainstem conduction time was found to be prolonged from 5.12+/-0.26 to 5.83+/-0.14 in neonates with a mean serum bilirubin level of 16.6 mg/dL (12 mg/dL to 18 mg/dL), which was found to be additionally prolonged to 6.0+/-1.0 with an increase in mean serum bilirubin level to 21.98 mg/dL (P < .01). At first retest after 1 month, 33.33% of cases with a mean serum bilirubin level of 19.46 mg/dL and 80.00% with a mean serum bilirubin level of 15.97 mg/dL showed total recovery. After 6 months, three cases with mean serum bilirubin levels of 26.3 mg/dL and one case with a mean serum bilirubin level of 17.7 mg/dL failed to show any improvement.

CONCLUSION

A positive correlation was found between increasing levels of serum bilirubin and brainstem conduction time (P < .01). ABR was found to be a very sensitive tool in picking up the earliest signs of neurotoxicity. Neonates with distortion of normal wave patterns on ABR were found to have poorer prognosis compared with those with delayed inter-peak (I-P) latencies.

Comparative ABR profile in high risk infants

Auditory brainstem responses (ABR) were studied in 52 children upto the age of 3 months, suffering from neonatal jaundice, prematurity, pyogenic meningitis and septicemia. Absolute latency of wave I and interpeak latency I-V were found to be significantly delayed in cases of jaundice and absolute latency of wave V and interpeak latency I-V were prolonged in cases with prematurity. In cases following pyogenic meningitis absolute latency of wave V and interpeak latency of I-III, I-V were significantly delayed compared to septicemia where absolute latency I, V and interpeak latency I-V were significantly delayed (P < 0.05). Maximum auditory insult was seen in cases with neonatal jaundice where 30.77% each had severe SN deafness and 30.77% had moderate degree of deafness compared to prematurity, meningitis and septicemia where 14.28, 7.69 and 25% were found to have severe SN deafness and 7.14, 38.46 and 25% had moderate deafness. Overall incidence of deafness of any kind in these factors was 44.23%.

The effects of neonatal jaundice and respiratory complications on learning and habituation in 5- to 11-month-old infants

The influences of neonatal hyperbilirubinemia and respiratory complications were examined in 5- to 11-month-old infants in two studies. One study focused on habituation performance and the other on contingency learning. In both experiments, three neonatal jaundice conditions (no jaundice history, measured bilirubin, phototherapy) were crossed with two levels of neonatal respiratory risk (no oxygen intervention, oxygen intervention). For low respiratory risk subjects there were increasingly adverse effects for both habituation and learning the more severe the jaundice history. A complex pattern emerged for the high respiratory risk groups. Only for the learning task were the results consistent with a summative effect of neonatal jaundice and respiratory risk factors.

Brain-stem auditory evoked responses to hypercarbia in preterm infants

To determine the effect of acute hypercarbia on brain-stem function in preterm neonates, we compared brain-stem auditory evoked responses (BAERs) during 8% CO2 breathing to those elicited during room air breathing in 12 healthy preterm infants during the first week of life. End-tidal CO2 (ETpCO2), respiratory rate and depth were monitored throughout the protocol. Absolute wave latencies and interpeak intervals of the BAERs were analyzed from duplicate trials. During 8% CO2 breathing, ETpCO2, respiratory rate and depth of respiration increased significantly (P < 0.05). The absolute latency of wave V was prolonged (P < 0.025) in the hypercarbic state as compared to baseline. Interpeak interval III-V was also prolonged (P < 0.025). Values of absolute peak latencies I and III were unaffected by the hypercarbic state. These data demonstrate that elevations in pCO2 which elicit ventilatory responses also effect the BAER. The specific effects on ventilatory pattern, peak V latency and interpeak interval III-V indicate brain-stem responsiveness and alterations in the more central components of the auditory pathway. These findings raise important considerations regarding the influence of hypercarbia on brain-stem function in preterm infants and the clinical management of such infants with abnormalities of gas exchange.