Phototherapy: Current methods and future directions
Section snippets
Photobiology of bilirubin
The rate of removal of unconjugated bilirubin from the body during phototherapy depends on the following three related processes: (1) the rate of bilirubin photoalteration; (2) the transport of photoproducts from the skin to the circulation; and (3) the excretion of these photoproducts by the liver and kidney.2, 5, 6 Of these processes, the photoalteration of bilirubin (Fig. 1) is a complex set of photochemical reactions and believed to be the rate-limiting step in the elimination of bilirubin
Efficacy
The therapeutic efficacy of phototherapy is dependent primarily on the following factors: the spectral qualities of the delivered light (wavelength range and peak),b intensity of light (irradiance), exposed body surface area (BSA), skin thickness and pigmentation, the total bilirubin at clinical presentation, and duration of exposure.
Spectral qualities
The optimum light quality for the most efficient use of phototherapy is still under active investigation and discussion.5, 9 The yellow bilirubin absorption spectrum in plasma and in buffer/human serum albumin has been well established. In general, the in vitro bilirubin light absorption spectrum is used as the basis for the design of phototherapy light sources. Thus, the most effective light sources for degrading bilirubin in the skin and the circulation are those that emit light in a
Irradiance
Irradiance or light intensity refers to the number of photons as directed to or received per square cm of the exposed BSA. Because the irradiance is quantitated as μW/cm2 within the effective wavelength range for efficacy, it is also referred to as “spectral irradiance” and is expressed as μW/cm2/nm.13 “Deliverable spectral irradiance” is different for each type of light source, and is dependent on the its design and the distance between the light source and patient in an inverse square root
Exposed surface area
Effective phototherapy is very much dependent on exposure to the largest BSA of the newborn. The greater the area exposed, the greater the rate of total bilirubin decline.15 At present, the limited BSA exposure by all light sources is the greatest impediment to effective phototherapy. In general, with the present overhead and underneath devices used singly, only up to 30% of BSA is exposed to light. The variability and limitation is attributable to the dimensions of a device’s light footprint
Skin thickness and pigmentation and initial total bilirubin level
Patient parameters, such as increases skin thickness (ie, in older Crigler-Najjar patients)17 and highly pigmented skin, have been reported to impede effective phototherapy.18 Furthermore, the initial total bilirubin level as well as an imbalance between bilirubin production and elimination also negatively affects phototherapy efficacy.19
Duration of exposure
Although duration of exposure to elevated total bilirubin levels could be an important factor in understanding risk for acute bilirubin encephalopathy or kernicterus, information about the duration of bilirubin exposure is generally lacking in the literature. Moreover, most of the literature addressing risk has been focused on peak total bilirubin levels. This limited perspective may need to be broadened to include the duration of exposure to total bilirubin or its fractions and is discussed
Side effects
More effective phototherapy probably represents less risk for the newborn, assuming that, in the photochemical reactions, the light does not affect molecules other than bilirubin. This latter possibility is one that should be explored more seriously for smaller, less mature and more translucent newborns, who are often treated with photosensitizing drugs, such as riboflavin (RF), Vitamin K, and others. RF, a powerful endogenous photosensitizer, which has been extensively studied, decreases
Current light sources
There is a considerable selection of various custom-made and commercial phototherapy devices, which have been produced for investigative and clinical applications. However, a complete discussion of these is beyond the scope of this review. In summary, phototherapy devices can be categorized by their light source as follows: (1) fluorescent tube (TL12, 60 cm, 20W) devices with different colors of light [cool white (CW), blue, special blue (BB, 52, and 03), turquoise, or green] of straight or
“Blue hue” effect
Blue light may be most therapeutic for jaundiced infants, but caregivers have reported a range of “irritations” from the use of blue fluorescent tubes, including headaches, nausea, and vertigo.31 Initially, it was thought that the direct current (DC)-powered, LED-based devices would be free of such effects because this light does not “flicker” at 50 to 60 Hz/sec, as do AC-powered fluorescent tubes. This appears not to be the case and the true cause for the visual irritation is more likely due
Conclusions
In conclusion, phototherapy is one of the most common medical interventions with well-established efficacy and probably safety for most short-term applications in near-term and term infants with neonatal hyperbilirubinemia. There has been recent clarification of management of hyperbilirubinemia in the newborn infant 35 or more weeks of gestation with the publication of the AAP guideline with direct recommendations for the application of phototherapy. Nonetheless, a better understanding of the
Acknowledgments
This work was supported by unrestricted gifts from the H.M. Lui Research Fund, the Hess Research Fund, and the Mary L. Johnson Research Fund.
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