Dag Bratlid

Bilirubin and Brain Toxicity

More than a century has passed since Hervieux first described yellow staining of the basal ganglia in association with neonatal jaundice (1). The term kernicterus was, however, first used by Schmorl in 1904 to describe the post-mortem finding of yellow staining of the basal ganglia in term infants whose cause of death was probably feto-maternal iso-immunization (2). This term has since been used to describe both the acute, often fatal condition in the newborn with substantial elevation of serum bilirubin levels, seizures, opisthotonus, and bleeding tendency, as well as the neurologic sequelae in survivors, consisting of choreoathetosis, asymmetric spasticity, paresis of upward gaze, and neurogenic hearing loss (3-7). Yellow staining of the brain has, in recent years, also been observed in infants dying without the clinical symptoms of kernicterus, and in whom only moderately elevated serum bilirubin values had been noted (8-10). Bilirubin has, in addition, been implicated in damage to cognitive functions (11, 12), but consensus is lacking regarding permanent damage to such functions (13, 14). The terms kernicterus and bilirubin encephalopathy have often been used interchangably, and without any clear definition of the terms. We suggest that bilirubin encephalopathy should be used in a broader sense so as to include all conditions in which bilirubin is known, or thought to be, the cause of brain toxicity. The term kernicterus would be reserved for cases exhibiting the classical acute symptoms described above, or surviving with the typical neurologic sequelae. During the past thirty years, considerable research has been carried out regarding the causes of hyperbilirubinemia and the mechanisms underlying bilirubin toxicity. Despite these efforts the basic mechanisms remain elusive. This research has been concentrated on three main areas. Firstly, the binding of bilirubin to albumin has been investigated in detail. Secondly, a number of studies have addressed the toxicity of bilirubin both in nervous tissue, and in other cell and organ systems. Finally, the mode of entry of bilirubin into the central nervous system has been examined.

The effects of variations in PaCO2 on brain blood flow and cardiac output in the newborn piglet.

ABSTRACT. The acute effects of normoxemic hypocarbia and hypercarbia were examined in six newborn piglets. Brain blood flow was maintained during hypocarbia until extremely low Paco2 (<15 mm Hg) levels were achieved at which time total brain and cerebral blood flow decreased significantly from baseline values. Blood flow to the thalamus, cerebellum and brain stem was unchanged from baseline conditions during hypocarbia. This suggests that the newborn brain is relatively insensitive to moderate degrees of hypocarbia. Extreme hypocarbia (Paco2 <15 mm Hg) was associated with a significant increase in heart rate, accompanied by a significant decrease in mean arterial blood pressure; however, cardiac output was not significantly different from baseline determinations. Hypercarbia with normoxemia was associated with significant increases in total brain blood flow, with greater blood flow to the brain stem, cerebellum, and thalamus than to the cerebrum. The percentage of cardiac output received by the brain was also significantly increased, although total cardiac output was unchanged. This demonstrates that the newborn cerebral vasculature is sensitive to hypercarbia and that regional differences in sensitivity may account for the greater increments in blood flow to the caudal portions of the brain than that to the cerebrum.

Incidence and prediction of bronchopulmonary dysplasia in a cohort of premature infants

Farstad T, Bratlid D. Incidence and prediction of bronchopulmonary dysplasia in a cohort of premature infants. Acta Pzdiatr 1994;83:19–24. Stockholm. ISSN 0803–5253

The Effects of Brain Blood Flow on Brain Bilirubin Deposition in Newborn Piglets

ABSTRACT: Since kernicteric lesions are usually found in the subcortical regions of the brain and these areas also receive the highest blood flow during asphyxia and hypercapnia, we hypothesized that increases in brain bilirubin deposition may be related to increases in brain blood flow. Fourteen piglets underwent a 3-h infusion of bilirubin to maintain total serum bilirubin at approximately 8 mg/dl, during which time blood gases, hemodynamic variables, and brain blood flow were determined. After sacrificing the animals, regional brain bilirubin content was determined. Ten piglets underwent the same protocol; in addition, hypercapnia was induced during the last hour of study (Paco2 approximately 70 mm Hg). The regional brain blood flow and bilirubin deposition were significantly increased over control values (p < 0.05) following hypercapnia in the subcortical region and significantly so in the midbrain and cerebellum. In separate groups of control (n = 6) and hypercapnia (n = 6) piglets, 125I-labeled albumin was infused and demonstrated that hypercapnia was not associated with increased regional brain albumin content. We conclude that hypercapnia-induced augmentation in regional brain blood flow is associated with increased deposition of unbound bilirubin. Although the causal relationship between these two observations has not been firmly established, the findings deserve future investigation to clarify the role of brain blood flow, brain bilirubin deposition, and the production of kernicterus in high risk infants.

In vitro Binding of [3H]Bilirubin to Neurons in Rat Brain Sections

Slide-mounted 12-microns cryostat sections of rat brain were incubated with [3H]bilirubin, washed, dried, and apposed to emulsion-coated coverslips for autoradiography. The binding appeared to be nonsaturable. Within the gray matter, binding was concentrated over neuronal cell bodies (particularly evident over hippocampal pyramidal and granular cells, and over cerebellar Purkinje cells), suggesting that the preferential neuronal toxicity of bilirubin may be related to neuronal binding. Regional differences in bilirubin binding were not demonstrated.

Cerebral Blood Flow during Experimental Hypoxaemia and lschaemia in the Newborn Piglet

Odden, J.‐P., Stiris, T., Hansen, T. W. R. and Bratlid, D. (Neonatal Research Laboratory, Department of Paediatric Research, Institute for Surgical Research and Department of Paediatrics, Rikshospitalet, University of Oslo, Oslo, Norway). Cerebral blood flow during experimental hypoxaemia and ischaemia in the newborn piglet. Acta Paediatr Scand Suppl 360: 13, 1989.

Open-field behavior of rats previously subjected to short-term hyperbilirubinemia with or without blood-brain barrier manipulations

The aim of this study was to investigate (i) whether bilirubin encephalopathy with lasting sequelae could be created in a rat model, and (ii) putative differences in brain toxicity between bound and unbound bilirubin. Hyperbilirubinemia was produced by infusing bilirubin 20 mg/kg/h during 3 h into 6-week-old male Sprague-Dawley rats. In addition to the hyperbilirubinemia, different groups were created by exposing the rats to hyperosmolality, hypercarbia, and sulfisoxazole. Three weeks after the infusion the rats were studied in an open-field apparatus during 10 daily sessions of 15 min duration. A data collection program was used to study the following measures of activity: crossings in cage, peeks, rearing, latency to enter field, crossings in middle and in outer field, and time outside cage. The data were subjected to multivariate analyses of variance (MANOVA). Generally, the level of activity was higher in the bilirubin-treated rats as compared to the control animals. The difference in activity between bilirubin-treated and control rats changed systematically both between and within sessions. The data show that both unbound and albumin-bound bilirubin are neurotoxic, but they indicate a more pronounced effect of unbound bilirubin. The sequelae of bilirubin brain toxicity appear to include changes in stimulus processing. This is compatible with findings from neuropsychological tests of children who have had significant neonatal hyperbilirubinemia.

Validity of Doppler measurements of superior mesenteric artery blood flow velocity: Comparison with blood flow measured by microsphere technique

Objective: To validate Doppler measurement of superior mesenteric artery blood flow velocity as a measurement of superior mesenteric artery blood flow. Method: The superior mesenteric artery blood flow velocity, measured by the Doppler ultrasound technique, was validated with simultaneous measurement of blood flow by the microsphere method. Six newborn piglets were studied during baseline conditions, after 10 min of hypoxaemia and during continuous calcium blocker infusion. Results: Mean blood flow velocity (r = 0.69, P < 0.0001), end-diastolic flow velocity (EDFV) (r = 0.81, P < 0.0001) and resistance index (r = 0.76, P < 0.0001) all correlated with superior mesenteric artery blood flow, whereas the peak systolic flow velocity did not correlate. Mean blood flow velocity did not significantly reflect all the changes in blood flow, probably because of changes in cross-sectional area of the superior mesenteric artery. The changes in EDFV followed the changes in blood flow more closely, although the decrease in EDFV (91% ± 12%) was of greater magnitude than the decrease in blood flow (55% ± 11%). Conclusions: Our results suggest that, although EDFV measurements in the superior mesenteric artery are not a predictor of quantitative changes in blood flow, it could be used to follow qualitative changes in intestinal blood flow under different clinical conditions.

Effect of hypoxemia and hypovolemia on retinal and choroidal blood flow in the newborn piglet

The effect of hypoxemia and/or hypovolemia on ocular blood flow was studied in paralyzed and mechanically ventilated newborn piglets with the isotope-labelled microsphere method. Twenty-six piglets were studied in four different groups. One group of piglets (n = 6) was made hypoxemic by breathing 10% O2, a second group (n = 7) and a third group (n = 7) were studied during hypoxemia (10% O2), followed by hypovolemia (bleeding 20 and 30% of estimated blood volume, respectively). A fourth group of piglets (n = 6) was made hypovolemic by bleeding 20% of estimated blood volume. Hypoxemia resulted in a 2- to 3-fold increase in retinal blood flow (RBF), while hypovolemia did not change RBF, not even when preceded by a period of hypoxemia. In the case of choroidal blood flow (ChBF), the increase caused by hypoxemia was only 10-40%. Although ChBF decreased significantly during hypovolemia, no significant correlation between mean arterial blood pressure and ChBF was found. The results indicate that autoregulation is normally seen in RBF, but probably not in ChBF. However, during hypoxemia autoregulation was found neither in RBF nor in ChBF.

Atropine Prevents Increases in Brain Blood Flow during Hypertension in Newborn Piglets

ABSTRACT. Cerebral hyperperfusion associated with hypertension, may play an important role in the pathogenesis of intraventricular hemorrhage in preterm infants. To examine the effect of hypertension on changes in total and regional brain blood flow (BBF), we increased the mean arterial blood pressure (MABP) in nine awake newborn piglets by an infusion of 0.7 mg/kg of metaraminol bitar-trate (Aramine) (group I) and studied cerebral circulatory changes. In order to prevent the Aramine-associated bradycardia, we pretreated nine other piglets with atropine, which produced a higher level of hypertension (group II). MABP and BBF were measured and cerebral vascular resistance (CVR) was calculated during baseline, the Aramine infusion, and twice at decreasing MABP following the discontinuation of the Aramine infusion. In group I, the significant increase in MABP from 68 ± 3 to 100 ± 3 mm Hg (mean ± SEM) during the Aramine infusion resulted in a significant increase in BBF (98 ± 9 to 118 ± 11 ml-min−1 100 g−1)- MABP decreased significantly (although remained significantly above baseline levels), when Aramine was discontinued; however, total BBF remained elevated. CVR increased during the Aramine infusion, but decreased significan (versus the Aramine-infused state) in the post-Aramine period. Regional BBF increased significantly to the cerebrum and cerebellar cortex, but remained unchanged to the other regions including the brain stem. In group II, the Aramine infusion resulted in a significantly greater increase in MABP, a sustained increase in vascular resistance, and no increase in total BBF. Thus, atropine prevents increased BBF during hypertension in the newborn piglet.