Skin optics and phototherapy of jaundice

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.

Fluorescence excitation spectrum of bilirubin in blood: a model for the action spectrum for phototherapy of neonatal jaundice

A recent report (Lamola et al. 2013 Pediatric Research, 74, 54-60) presents a semiempirical model for facile calculation of an action spectrum for bilirubin photochemistry in vivo using the most current knowledge of the optics of neonatal skin. The calculations indicate that competition for phototherapy light by hemoglobin in the skin is the predominant factor that defines the spectrum of light absorbed by bilirubin. If the latter is correct, a valid physical analog of the calculated spectrum is the excitation spectrum of bilirubin in blood. The fluorescence excitation spectrum was recorded and, indeed, found to be very similar to the calculated spectrum. Both spectra exhibit maxima near 476 nm and widths at half height of about 50 nm. This result supports the conclusion that light between 460 and 490 nm is most effective for phototherapy of neonatal jaundice.

The effect of hematocrit on the efficacy of phototherapy for neonatal jaundice

BACKGROUND

The therapeutic phototherapy action spectrum ranges from 420 to 500 nm. However, a recent report of improved efficacy of fluorescent "turquoise" light (~490 nm) as compared with blue light (~450 nm) underscores the need to define an optimal action spectrum for precision-targeted phototherapy using very narrow wavelength ranges.

METHODS

We used a current semi-empirical model of the optical properties of skin for robust calculations of the fraction of light absorbed by bilirubin at various wavelengths that could be confounded by hemoglobin (Hb), melanin, and skin thickness. Applying assumptions regarding the wavelength dependence of bilirubin photochemistry, "action spectra" were assembled from the calculated values.

RESULTS

All the calculated action spectra displayed a peak between 472 and 480 nm (most at 476 nm), which is a significant shift from the well-reported 460 nm absorption peak of bilirubin. Of note, the relative amplitudes of the action spectra showed an inverse relationship with hematocrit (Hct).

CONCLUSION

We speculate that a narrow range of light at 476 nm would be 60% more effective than blue (broadband) fluorescent lamps. Because Hb serves as a major competitor of bilirubin for light absorption, the calculations also predict that the efficacy of phototherapy is dependent on the Hct. A high Hct could reduce therapeutic efficiency.

A prospective randomized controlled study of phototherapy using blue and blue-green light-emitting devices, and conventional halogen-quartz phototherapy

OBJECTIVE

To determine the efficacy of blue versus blue-green phototherapy using new light sources with narrow luminous spectra. The devices made of high-intensity gallium nitride light-emitting diodes (LEDs) were also compared to conventional halogen-quartz bulbs phototherapy.

DESIGN

Prospective open randomized study.

PARTICIPANTS

A total of 114 jaundiced, but otherwise healthy term infants who met the entry criteria for phototherapy set by the American Academy of Pediatrics' Practice Parameter.

MAIN OUTCOME MEASURES

The duration of phototherapy and the rate of decrease in total serum bilirubin (TSB).

RESULTS

The mean TSB concentrations at initiation and termination of treatment, as well as the duration of phototherapy and the rate of decrease in TSB, were not statistically different in newborns receiving blue LED, blue-green LED or conventional phototherapy. The average rate of decrease in TSB (slope), after adjustment by a linear regression analysis for confounding factors, was -3.61 micromol/hour (95% confidence limits -5.47, -1.75) in the 25 newborns receiving blue LED phototherapy compared with -2.57 micromol/hour (-4.32, -0.82) in the 22 newborns treated with blue-green LED phototherapy and -3.42 micromol/hour (-5.02, -1.81) in the 57 newborns who received conventional phototherapy.

CONCLUSIONS

When using low light irradiance, there was no statistically significant difference in the effectiveness of phototherapy using blue-green LEDs, blue LEDs or conventional halogen-quartz bulbs.

Effect of position changing on bilirubin levels during phototherapy

OBJECTIVE

Turning of infants during phototherapy for hyperbilirubinemia is practiced in many nurseries. However, there is little research evidence in support of this practice. This study examined the effect of turning on serum total bilirubin concentration and on the duration of phototherapy.

STUDY DESIGN

We first conducted a pilot study in term infants requiring phototherapy using transcutaneous bilirubinometry in order to determine the time required to clear the skin of bilirubin. This "blanching time" was found to be approximately 150 minutes. We then conducted a randomized study comparing turning the baby during phototherapy with care in the supine position only.

RESULTS

Thirty term infants were enrolled in the study (turned - 14; supine - 16). No differences were found between the groups in baseline data, such as birth weight, gestational age, age at start of phototherapy, or type of feeds. Infants in the supine group showed a significantly larger drop in serum total bilirubin concentration and required a shorter duration of phototherapy.

CONCLUSION

We conclude that infants should be nursed supine during phototherapy. Based on these results, we propose a modification to the traditional model of bilirubin kinetics during phototherapy.

Quantum yield and skin filtering effects on the formation rate of lumirubin

Photocyclization of bilirubin to lumirubin in the skin of jaundiced infants exposed to blue-green light irradiation is considered to be the most important process for bilirubin elimination from the organism. The quantum yield phi LR of the bilirubin-->lumirubin photoreaction has been recently measured and found to vary with the excitation wavelength, with a peak at about 520 nm. The quantum yield phi ZE for the strongly competing reversible configurational photoisomerization of bilirubin has also been recently shown to be wavelength dependent and to decrease significantly in the long-wavelength part of the absorption band of bilirubin. These new data are taken into account to model the bilirubin photochemistry in vivo by using a simplified skin optical model based on the Kubelka-Munk theory. The rate kappa LR of formation of lumirubin has been evaluated for the case of a four-layer skin and for monochromatic and narrow-band coloured fluorescent lamps. The effects of long-wavelength increase in phi LR, decrease in phi ZE and skin optical losses all combine to shift significantly the optimal rate of formation of lumirubin towards the green. These results suggest that a significant improvement in phototherapy might be obtained with the introduction of new lamps emitting in the blue-green spectral region between 490 and 510 nm.

Bilirubin bound to cells does not form photoisomers

Cultured cells from one human and one murine cell line were incubated with bilirubin by different methods that allowed bilirubin to be bound to cells. The cells were irradiated with visible light of different wavelengths. Bilirubin bound to human serum albumin was also irradiated with light. After irradiation, bilirubin and its photoisomers were extracted and analyzed by HPLC. No photoisomers were found in samples of irradiated cells, while the types and amounts of photoisomers that were expected from the literature were found in samples of irradiated bilirubin/albumin mixtures. We conclude that the formation of therapeutically active photoisomers during phototherapy most probably does not take place in skin cells, but most likely in bilirubin bound to albumin in the vessels or in the interstitial space.

Quantum yields for laser photocyclization of bilirubin in the presence of human serum albumin. Dependence of quantum yield on excitation wavelength

The quantum yield for laser photocyclization of bilirubin to lumirubin in the presence of human serum albumin (phi LR) was measured at five monochromatic excitation wavelengths in the range 450-530 nm. Solutions used were optically thin throughout the wavelength range and precautions were taken to exclude contributions from photocyclization of bilirubin XIII alpha impurities. The values obtained (7.2-18 x 10(-4] were lower than those previously reported and showed the following wavelength dependence: 457.9 less than 488.0 less than 501.7 less than 514.5 approximately equal to 528.7. However, the rate of lumirubin formation, normalized to constant fluence, decreased with wavelength over the same wavelength range and no evidence was found that photoisomerization of bilirubin to lumirubin is faster with green (514.5 or 528.7 nm) than with blue (457.9 or 488.0 nm) light. The stereoselectivity of the configurational isomerization of bilirubin to 4Z,15E and 4E,15Z isomers also was studied. This reaction became less regioselective for the 4Z,15E isomer with increasing wavelength. The observed wavelength dependence of phi LR and of the [4E,15Z]: [4Z,15E] ratio at photoequilibrium are consistent with an exciton coupling model in which intramolecular energy transfer can occur between the two pyrromethenone chromophores of the bilirubin molecule in the excited state. Relative rates of lumirubin formation in vivo at different excitation wavelengths and constant fluence were estimated for different optical thicknesses and for different skin thicknesses. These estimates suggest that the recently reported clinical equivalence of blue and green phototherapy lights probably reflects the marked variation of skin transmittance with wavelength more than wavelength-dependent photochemistry. The calculations also indicated that the optimal wavelength for phototherapy is probably on the long wavelength side of the bilirubin absorption maximum.

Phototherapy in a new light

Visible light phototherapy has been used in the treatment of neonatal jaundice for more than 25 years. This article reviews the current state of knowledge of how phototherapy works and provides a framework for understanding why green may soon become the color of choice for phototherapy lamps.

Phototherapy for neonatal jaundice: clinical equivalence of fluorescent green and "special" blue lamps

The relative efficacy of fluorescent green (Sylvania F20T12/G) and "special" blue (Westinghouse F20T12/BB) lamps in the phototherapy of jaundiced neonates was investigated. Two groups of low birth weight infants with a mean gestational age of 35 weeks and mean birth weight of 1930 gm, who developed hyperbilirubinemia within the first 5 days of life, were given green or blue lamp phototherapy under the same irradiation conditions. No statistically significant difference in plasma bilirubin concentrations was found between the two groups after 24 or 48 hours of treatment. Because recent measurements indicate that green lamps are much less efficient than special blue lamps for the production of Z, E isomers of bilirubin in vitro and in vivo, the clinical equivalence of these two types of lamps seems to support the hypothesis that production of structural photoisomers of bilirubin is the main mechanism of phototherapy in humans. Therefore, fluorescent green lamps provide an alternative to special blue lamps for treatment of neonatal hyperbilirubinemia.