The Pattern of Bilirubin Response to Phototherapy for Neonatal Hyperbilirubinaemia

Abstract

SummaryThe pattern of bilirubin response to phototherapy was studied using lamps with an emission spectrum closely similar to the bilirubin absorption spectrum. A dose-response relationship was demonstrated, with increased intensity of phototherapy resulting in greater response; however, the rate of bilirubin decline progressively decreased with increasing radiance till a 'saturation' point was reached, beyond which no further response occurred with further increase in radiance, suggesting a curvilinear relationship of the nature of an asymptotic regression. At the 'saturation' point, a 24-h decline of about 50% was achieved.With extended periods of phototherapy, a gradually decreasing response to phototherapy with declining bilirubin levels was 06served. both with maximal or moderate intensitv vhototheravv; an exponential regression was suggested. At abbit 5 mg/di iktfe further decline was observed with continued phototherapy. The rate of the 24-h decline evaluated at 6-h intervals was observed to be proportional to the bilirubin level at the start of the 24-h period.

Phototherapy — Traditional and Nontraditional

“…With standard phototherapy systems, decreases of 6% to 20% of the initial bilirubin level can be expected in the first 24 hours. 16,19,21 Although Tan's data 12 suggest that there is a saturation point beyond which an increase in the irradiance produces no added efficacy we do not know for a certain that a saturation point exists.…”

“…13 ''Spectral 12 has demonstrated the direct relationship between the irradiance used and the efficacy of phototherapy (Figure 3). Figure 4 shows that the light intensity (measured as spectral irradiance) is inversely related to the distance from the source.…”

“…Although most of the information needed to deliver this intensive form of phototherapy has been available for many years, most full-term infants still receive phototherapy in a dose that is well below the optimum therapeutic range. 12 This ''new phototherapy'' has arisen out of the recognition that phototherapy requires the same sort of approach that is applied to drug therapy -an understanding both of the dose-response effect and the influence of other factors on the way light works to lower the serum bilirubin level (just as absorption and volume of distribution affect the efficacy of a drug). When a phototherapy light is turned on, the infant receives an infusion of discreet photons of energy similar to the molecules of a drug in a medication.…”

Phototherapy: The challenge to accurately measure irradiance

“…An earlier in vivo study (5) and our recent bench data(6) illustrate the dose-response relationships of phototherapy as a direct relationship between the irradiance used and the rate at which the serum/ plasma bilirubin declines under blue light phototherapy. Each blue light source typically emits a specific spectral range of photons with a characteristic peak emission.…”

“…It is now well established that an effective phototherapy device needs to deliver light with (a) a light emission spectrum within the bilirubin absorption spectrum (400-520nm); (b) a peak emission of 450±20nm; (c) an irradiance foot print which exposes at least one horizontal body surface plane or optimally the entire circumferential (360º) body surface area; (d) an irradiance level ≥30 µW/ cm 2 /nm, as measured with an appropriate irradiance meter; and, (e) optimized duration of exposure (3)(4)(5). Many phototherapy devices with light sources such as blue and special blue fluorescent tubes, halogen, and halogen/fiberoptic, and most recently, light emitting diode-based (LED) lamps have been developed and marketed.…”