Urinary excretion of tryptophan metabolites during phototherapy

Blue-Green (~480 nm) versus Blue (~460 nm) Light for Newborn Phototherapy-Safety Considerations

We have previously shown that the phototherapy of hyperbilirubinemic neonates using blue-green LED light with a peak wavelength of ~478 nm is 31% more efficient for removing unconjugated bilirubin from circulation than blue LED light with a peak wavelength of ~452 nm. Based on these results, we recommended that the phototherapy of hyperbilirubinemic newborns be practiced with light of ~480 nm. Aim: Identify and discuss the most prominent potential changes that have been observed in the health effects of phototherapy using either blue fluorescent- or blue LED light and speculate on the expected effects of changing to blue-green LED light phototherapy. Search the phototherapy literature using the terms neonate, hyperbilirubinemia, and phototherapy in the PubMed and Embase databases. Transitioning from blue fluorescent light to blue-green LED light will expose neonates to less light in the 400-450 nm spectral range, potentially leading to less photo-oxidation and geno-/cytotoxicity, reduced risk of cancer, and decreased mortality in extremely low-birthweight neonates. The riboflavin level may decline, and the increased production and retention of bronze pigments may occur in predisposed neonates due to enhanced lumirubin formation. The production of pre-inflammatory cytokines may rise. Hemodynamic responses and transepidermal water loss are less likely to occur. The risk of hyperthermia may decrease with the use of blue-green LED light and the risk of hypothermia may increase. Parent-neonate attachment and breastfeeding will be positively affected because of the shortened duration of phototherapy. The latter may also lead to a significant reduction in the cost of phototherapy procedures as well as the hospitalization process.

Action spectrum of phototherapy in hyperbilirubinemic neonates

BACKGROUND

Phototherapy with blue light matching plasma absorption spectrum of the bilirubin-albumin complex with peak at 460 nm is standard treatment of neonatal hyperbilirubinemia.

AIM

To demonstrate clinically the action (efficacy) spectrum of phototherapy in hyperbilirubinemic neonates, through determination of the fraction of total serum bilirubin (TSB) decreased by phototherapy with peak emission wavelengths ≥478 nm (blue-green) compared with that of light of 459/452 nm (blue).

METHODS

TSB values were compiled from three earlier trials, in which hyperbilirubinemic neonates were randomized to receive 24 h of either blue-green light (478/490/497 nm) (intervention groups) or blue light (459/452/459 nm) (control groups) with equal irradiance and exposed body surface areas. Ratios (efficacy) between the decrease in TSB between intervention and control groups were calculated and graphed versus peak wavelengths, demonstrating the course of the action spectrum.

RESULTS

Calculated efficacy ratios were 1.31, 1.18, and 1.04 for light with peak wavelengths of 478, 490, and 497 nm, respectively. The action spectrum increases from 452/459 to maximum at 478 nm, from where it decreases to 1.18 and finally to 1.04.

CONCLUSION

For optimal phototherapeutic treatment, neonates need to be exposed to light with peak wavelength some 20 nm longer than is presently used.

IMPACT

The action (efficacy) spectrum of phototherapy for hyperbilirubinemic neonates has its peak wavelength at 478 nm. The peak wavelength of this action spectrum is 20 nm longer than the wavelength presently believed to be most efficient. The peak is also different from the peak found in vitro. For optimal phototherapeutic effect, neonates need to be treated with light of wavelengths some 20 nm longer than are presently used.

Incidence of thrombocytopenia following phototherapy in hyperbilirubinemic neonates

BACKGROUND

Thrombocytopenia has not been conclusively reported as a complication of phototherapy in any of the standard paediatric textbooks.

MATERIALS AND METHOD

A prospective study in consecutively enrolled cohort of apparently healthy neonates, who developed indirect hyperbilirubinaemia and required phototherapy. Neonates having a base line platelet count of more than 150,000/mm(3) were included. Neonates having features suggestive of haemolysis, direct hyperbilirubinaemia, sepsis, anti-platelet drugs given to baby or mother, haemangioma, and other congenital anomalies were excluded. Platelet counts were performed at admission, 24 hours, 48 hours, and before discontinuing phototherapy.

RESULTS

Out of 100 neonates included in study 35 (35%) had thrombocytopenia and a majority of neonates had mild thrombocytopenia (74%). The thrombocytopenia was seen in 26 (74%) cases during the first 24 hours of phototherapy and usually was not associated with clinical bleed.

CONCLUSION

This study establishes an association of phototherapy as a cause of thrombocytopenia in hyperbilirubinaemic neonates. Though the incidence of thrombocytopenia is substantial yet it is clinically insignificant. This study helps the practitioner to be aware of this association and avoid unnecessary investigations, as thrombocytopenia was transient.

Endothelium-dependent production and liberation of kynurenic acid by rat aortic rings exposed to L-kynurenine

Rat aortic slices produced and liberated the endogenous antagonist of glutamate receptors, kynurenic acid, upon exposure to L-kynurenine. Endothelium-denuded slices did not synthesize any measurable amount of kynurenic acid, indicating its endothelial origin. Aortic kynurenic acid production was diminished by modification of the ionic milieu, hypoxia and hypoglycemia, as well as by L-glutamate and L-aspartate, endogenous glutamate receptor agonists, and aminooxyacetic acid, a non-selective inhibitor of aminotransferases and mitochondrial respiration. These data pave the way for future research aimed to clarify the role of kynurenic acid in the physiology and pathology of the endothelium and vasculature.

Ultraviolet light burn: a cutaneous complication of visible light phototherapy of neonatal jaundice

Visible light phototherapy is an easily administered and effective treatment for neonatal indirect hyperbilirubinemia. Reported cutaneous side effects include transient rashes and the uncommon bronze baby syndrome. A more hazardous side effect is ultraviolet burn. Two premature infants developed phototherapy-induced erythema, one associated with a second-degree burn, after exposure to fluorescent daylight bulbs inadvertently used without Plexiglass shields, thus allowing prolonged ultraviolet A (UVA) exposure. Premature infants, especially during the first two weeks of life, may be significantly susceptible to UVA-induced erythema. Plexiglass shields should always be in place during visible light phototherapy, and nursery staff should be made aware of their purpose.

Molecular basis of hyperbilirubinemia and phototherapy

Hyperbilirubinemia in the newborn results not only in visible yellow discoloration of the skin but, in high concentration, may cause bilirubin encephalopathy. Such damage to the central nervous system may be subtle and not apparent for several years, as with visual-motor perceptive defects; or it may cause severe neurologic damage (Kernicterus)--even death. Sick and immature infants are the most vulnerable to bilirubin toxicity. Although this condition affects nearly half of all newborns to some degree, only about 10% require treatment. Two methods of treatment are really effective in correcting hyperbilirubinemia, exchange blood transfusions, and/or phototherapy with light radiation in the blue part of the visible spectrum. If the rate of production of bilirubin is excessive or an infant's capacity to conjugate and excrete the pigment is deficient, bilirubin will accumulate in plasma, and will be taken up by other lipid-containing tissues, collagen, and (unless firmly bound to albumin) brain tissue. Many factors combine to raise plasma levels of bilirubin to toxic levels; for example, acidosis, sepsis, hypoxia, hemolysis, hypoalbuminemia, and certain competitive albumin binders. Bilirubin is photolabile in vivo, and if the whole body is irradiated with visible light in the absorption band (450-490 nm) of bilirubin, the pigment will undergo photocatabolism. Under phototherapy bilirubin undergoes photoisomerization at the meso double-bond to conformations less lipophyllic. It is now known that the major photo products of bilirubin IX-alpha are an unresolved mixture of its E, Z and Z, E isomers, easily excreted by the liver. Thus, phototherapy will reduce the accumulation of bilirubin in skin and other tissues and in circulating plasma.

Evidence of riboflavin depletion in breast-fed newborns and its further acceleration during treatment of hyperbilirubinemia by phototherapy

Phototherapy in the treatment of newborns with hyperbilirubinemia, resulting in degradation of bilirubin, also appears to have other photodynamic effects on metabolism. We studied flavin adenine dinucleotide (FAD) saturation of erythrocyte glutathione reductase, which should reflect riboflavin nutritional status, in 28 healthy newborns, and followed 37 newborns with hyperbilirubinemia prior to the start of and during phototherapy. The results indicate that healthy newborns on human milk feeding, relatively poor in riboflavin, have evidence of a transient riboflavin depletion soon after birth. This effect is made more pronounced by phototherapy and partially prevented by parenteral or oral administration of moderate amounts of riboflavin.

Light (phototherapy)--induced riboflavin deficiency in the neonate

Phototherapy with blue light decomposes riboflavin, which has a maximum absorption at 450 nm. A study was designed to determine whether riboflavin deficiency developed in neonates who received phototherapy for moderate hyperbilirubinemia. Twenty-one infants with normal erythrocyte glucose-6-phosphate dehydrogenase activity were investigated. Five infants with moderate hyperbilirubinemia who did not require phototherapy served as the controls. Riboflavin deficiency was determined from the degree of saturation of erythrocyte glutathione reductase, a method shown to reflect riboflavin nutritional status in the neonate. Sixteen of 21 infants who were exposed to phototherapy developed riboflavin deficiency; all who had phototherapy for 49 hours or more developed the deficiency. That the concentration of serum bilirubin or the duration of hyperbilirubinemia was not a factor is supported by the fact that none of the controls became deficient. This observation may have important metabolic and clinical consequences for the neonate.

Platelet injury during phototherapy

Phototherapy with blue fluorescent light is widely employed for treatment of neonatal hyperbilirubinemia. Functional, biochemical, and morphologic changes produced by blue fluorescent light in human platelets were identified and characterized. Platelet-rich plasma was exposed for up to 170 min to amounts of light equivalent to that used in phototherapy of neonatal hyperbilirubinemia. Within 110 min of light exposure, platelets were essentially no longer aggregable by ADP and connective tissue suspension and were depleted of ADP, ATP, and glycogen. Electron photomicrographs revealed these platelets to be swollen, depleted of glycogen granules and organelles, and to have ill-defined membranes. Platelet injury could be accelerated by adding a photosensitizing agent, hematoporphyrin, to platelet samples before exposure. In contrast, control platelets kept in the dark for 170 min or nonirradiated platelets resuspended in irradiated plasma maintained their integrity. The results indicate that platelets are damaged in vitro when exposed to amounts of blue light used in phototherapy.