Newborns with hyperbilirubinemia: usefulness of brain stem auditory response evaluation

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.

Analysis of transient otoacoustic emissions and brainstem evoked auditory potentials in neonates with hyperbilirubinemia

Hyperbilirubinemia is toxic to the auditory pathways and to the central nervous system, leaving sequelae such as hearing loss and encephalopathy.

Aim

to assess the hearing of neonates with hyperbilirubinemia, using transient evoked otoacoustic emissions (TOAEs) and brainstem evoked auditory potentials (BEAP). Prospective study.

Materials and Methods

we had two groups: GI (n-25), neonates with hyperbilirubinemia; GII (n-22), neonates without hyperbilirubinemia and without risk factors for hearing loss. All the neonates had up to 60 days of life and were submitted to TOAE and BEAP.

Results

12 neonates from GI and 10 from GII were girls and 13 from GI and 12 from GII were boys. TOAEs were present in all the children, however with lower amplitudes in GI, especially in the frequencies of 2 and 3KHz (p < 0.05). Regarding the BEAP, we observed a mild PV and LI-V increase in BI. The alterations observed in these tests do not correlate to the serum levels of bilirubin.

Conclusions

in neonates with hyperbilirubinemia, we noticed lower TOAE amplitudes and mild PV and LI-V increase, indicating cochlear and retrocochlear disorders, stressing the importance of using both tests and carefully reading them in these evaluations.

Understanding neonatal jaundice: UK practice and international profile

Over the last 25 years there have been considerable advances in the treatment and technologies used in the care of newborn infants. Most of these advances are related to the care of the premature infants and there have been few changes in the management of conditions commonly seen in term infants.

Neonatal jaundice is one of the commonest neonatal disorders and has been recognized since early history. Early neonatal jaundice is usually caused by the physiological destruction of red blood cells in the infant and its importance lies in the ability of the bilirubin pigment so produced to cross the blood brain barrier resulting in neurotoxicity. Prolonged neonatal jaundice (after 14 days of age) may be an indication of an underlying liver disorder. The approach to neonatal jaundice has remained largely unchanged over the last two to three decades. We continue to rely on visual inspection to assess the severity of early neonatal jaundice. We have technology that is effective in reducing the level of bilirubinaemia but in the UK there is no clear consensus as to the level at which jaundice should be treated. We do not have a standardized approach to the management of prolonged jaundice and there is potential for infants with significant liver problems to be diagnosed at a relatively late stage. Some countries (for example the US) have professional bodies who have introduced guidelines to ensure a standardized approach to the jaundice infant. We have little information about neonatal jaundice treatment in other parts of the developing world.

Short- and long-term outcome of severe neonatal nonhemolytic hyperbilirubinemia

We studied the effects of hyperbilirubinemia on brainstem auditory pathways and neurodevelopmental status in 99 full-term neonates with severe nonhemolytic hyperbilirubinemia (total serum bilirubin level = 301 to 500 micromol/L) born between 1995 and 2000. These were divided into three groups: group 1, moderate hyperbilirubinemia (n = 30; mean maximum total serum bilirubin = 320.7 micromol/L or 18.9 mg%); group 2, severe hyperbilirubinemia (n = 63; mean maximum total serum bilirubin = 369.0 micromol/L or 21.7 mg%); and group 3, super hyperbilirubinemia (n = 6; mean maximum total serum bilirubin = 457.2 micromol/L or 26.9 mg%). All received phototherapy, and three neonates also had exchange transfusion. Initial brainstem auditory evoked potentials were recorded in all at the mean age of 3.1 months (range 1-9 months). At initial assessment, only nine neonates (9.1%) had abnormal brainstem auditory evoked potentials. All except two returned to normal at 2 years. These two children had a hearing threshold at 50 nHL. We then compared serial brainstem auditory evoked potentials until 2 years for these nine cases with initial abnormal brainstem auditory evoked potentials, and nine cases with initial normal brainstem auditory evoked potentials were recruited for comparison. All 99 children had regular physical, neurologic, visual, and auditory assessments every 3 to 6 months until the age of 3 years. There was no significant correlation between demographic factors (gender, gestational age, or birthweight), maximum total serum bilirubin, and total serum bilirubin at discharge with an abnormal brainstem auditory evoked potential. There was no significant difference in the rate of brainstem auditory evoked potential abnormalities between the three groups: moderate (10%), severe (7.9%), and super (16.7%). All had normal neurodevelopmental status at 3 years. Only two children had transient mild motor delay and hypotonia, and both had normal brainstem auditory evoked potentials. There was no relationship between the abnormalities of the brainstem auditory evoked potentials and neurodevelopmental status. None of the three children receiving exchange transfusion had abnormal brainstem auditory evoked potentials or neurodevelopmental outcome. With the neurophysiologic and clinical outcomes in our cohort with severe nonhemolytic hyperbilirubinemia, we propose that the toxic effect of hyperbilirubinemia on auditory brainstem pathways might be transient provided that prompt treatment is initiated.

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.

Endocytosis in rat cultured astrocytes is inhibited by unconjugated bilirubin

Excessive hyperbilirubinemia can cause irreversible neurological damage in the neonatal period. However, the complete understanding of the pathogenesis of unconjugated bilirubin (UCB) encephalopathy remains a matter of debate. This study investigates whether UCB inhibits the endocytosis of cationized ferritin (CF) by cultured rat astrocytes. The relationship between endocytosis and MTT reduction, as well as changes on tubulin and glial fibrillary acidic protein (GFAP) assembly, were also evaluated. Inhibition of endocytosis was complete in the presence of 171 microM UCB, while a marked decrease of CF labeling was noticed for 86 microM UCB. In addition, MTT reduction was inhibited by 60 to 76% as UCB concentrations changed from 17 to 171 microM, while alterations on both GFAP and microtubule morphology were only achieved by cell exposure to 171 microM UCB. These findings indicate that inhibition of CF endocytosis in rat cortical astrocytes by UCB is a concentration-dependent process that appears to be primarily related to a direct effect on the cell membrane and not to any alteration of cytoskeletal microtubules and intermediate filaments.

Inhibition of glutamate uptake by unconjugated bilirubin in cultured cortical rat astrocytes: role of concentration and pH

The molecular basis of bilirubin toxicity to nerve cell function is still unclear. Since astrocytes are the main transporters of synaptically released glutamate and impaired glutamate uptake results in neuronal death, we investigated the effect of unconjugated bilirubin (UCB) on [(3)H]glutamate uptake in cultured rat astrocytes and the role of bilirubin ionization on toxicity. Astrocytes were incubated for 5-15 min, with UCB concentrations from 17 to 342 microM and UCB/albumin molar ratios of 0.2-3.0, at pH 7.0, 7.4, and 8.0. Exposure of astrocytes for 15 min to 85.5 microM UCB and 28.5 microM albumin resulted in a 63.1% decrease of glutamate uptake (p < 0.01). Interestingly, the effect demonstrated to be correlated with the UCB/albumin molar ratio (r = -0.986, p < 0.01) and a significant decrease was observed for a UCB/albumin molar ratio as low as 0.8. Inhibition of glutamate transport was also pH-dependent as it occurred at 7.4 (p < 0.05) and 8.0 (p < 0.01), but not at 7.0, suggesting that the monoanionic species of UCB accounted for the inhibition. These findings indicate that UCB, and more precisely the monoanionic species, impairs a crucial function of astrocytes such as glutamate transport and support a potential role of astrocyte function in the pathogenesis of UCB-related brain damage (kernicterus).